Power loss downhill
04-04-2005, 11:12 AM
#16
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I've had some powerloss/hesitation issues that were 'cured' temperarily by replacement of O2 sensor (logged as fault), dist caps and rotors and new 2nd dist belt(unrelated). Symptoms returned a few K's later but were sporadic, then had the cars 24k service and got my mech to investigate. He concluded that the Airflow sensor was to blame even though it seemed to look ok, readings were slightly out of factory spec and he also removed and cleaned the actual connector for the AFS. Car has run perfectly since and whilst it may not be your issue he says he's seen several cars where the cleaning up of the AFM contacts whilst simple has been sufficient to sort the problem. Hope you find the issue as i know how annoying they are 
04-04-2005, 12:25 PM
#17
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Originally Posted by Heirsh
Well i pulled the Air Flow meter this weekend. Not a lot I could do for it. It wasnt sticking, but I cleaned all the gunk from inside by spraying through with an electrical cleaner. I also popped the plastic cap to get at the electrical part of it. That is a piece of art there. Thankfully it was in good shape. I cleaned the outside plug connections, and used some electrical cleaner ont he inside, but otherwise didnt touch it. The car does drive better at very small throttle inputs so I guess I didnt ruin anything.
Bad thing is the problem with power less downhill still exists. I still plan to check the tank, but the more I think about it the more I just can't believe a gas tank obstruction could be doing this. More information on the problem.
If I blip the throttle going downhill the problem doesnt crop up, even on hills that always cause the problem.
I don't see how it can be related to the air flow meter, as it is before any vacuum that could be building it (all after the throttle butterflies). Also the vacuum would not be pulling the flap closed, it would be pulling it open, as it does under normal operation when the throttle butterflies open. So I'm thinking, if its related to vacuum, I need to be looking at things which use the vacuum between the butterflies and the engine. I wish my frickin repair manuals would get here. I don't see how you guys deal with this problem; it is driving me nuts.
Surely someone out there has fixed this problem as it seems to be relatively common. Fuel pump aging and cavitating at super low fuel consumption rates (this would, I guess, have to be in conjunction with a clog in the bypass as the pump should always be flowing right?). I don't know I'm grasping at straws. HELP!?
Bad thing is the problem with power less downhill still exists. I still plan to check the tank, but the more I think about it the more I just can't believe a gas tank obstruction could be doing this. More information on the problem.
If I blip the throttle going downhill the problem doesnt crop up, even on hills that always cause the problem.
I don't see how it can be related to the air flow meter, as it is before any vacuum that could be building it (all after the throttle butterflies). Also the vacuum would not be pulling the flap closed, it would be pulling it open, as it does under normal operation when the throttle butterflies open. So I'm thinking, if its related to vacuum, I need to be looking at things which use the vacuum between the butterflies and the engine. I wish my frickin repair manuals would get here. I don't see how you guys deal with this problem; it is driving me nuts.
Surely someone out there has fixed this problem as it seems to be relatively common. Fuel pump aging and cavitating at super low fuel consumption rates (this would, I guess, have to be in conjunction with a clog in the bypass as the pump should always be flowing right?). I don't know I'm grasping at straws. HELP!?
I would advise as I have said thousands of times on this forum and others to provide MORE details of your 964.
I cannot determine where in the world you are and this could play a significant role in helping in the troubleshooting.
NOT ALL 964s are the same. If you have a M150 engine for instance like possibly Mark in the UK has then the whole engine management system is controlled differently to a standard ROW or the USA version.
Please provide more details on the country status, option status, modification status and current location of the 964.
Ciao,
Adrian.
04-04-2005, 08:18 PM
#18
Burning Brakes
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Sure Adrian, thank you.
Location: Mountains of North Carolina, United States.
Car type: 1990 C2, (964 340)
Engine: M6401-62L G5003
Options: C02 158 220 454 494 650
I travel between an elevation of 1300 and 2800 ft. regularly. Lots of ups and downs so this problem is extremely annoying to me. Its still pretty much the same.
Slight downgrades and the problem develops. More severe downgrades and it does not. It also seems to be worse when turning and going slightly down. It acts liek there is no power available. If i back off the throttle it actually gets a tad of power back, like there is enough gas for the idle stage, but nothing else. When it starts to come back it sputters like it was flooded or is just getting gas back into the injectors (I'm not saying it was flooded, it just acts like it. If it was flooded letting it return to idle wouldnt make it suddenly run smooth). It doesnt seem to matter the temperature, humidity, or time of day. It doesnt matter how much fuel is in the tank.
Recently the car has developed another annoyance. It quickly loses power and gets it back. I doubt this is related, but I just mention it because it might be. I am going to try cleaning those connectors again on the afm. It's an instant thing, and I am pretty sure more than 1 cylinder.
Car is unmodified by me and as far as I can tell unmodifed by the previous owner. It was serviced at a dealership with all the papers. The previous owner complained of the same problem to the dealership, but they reported that they were unable to duplicate it.
Well I may as well state this problem as well. Idle is not smooth. It idles steady just above 800, and has never cut off on me. If I didnt know better I'd think it just has a lope from cams. I have a set of plugs to replace when I get the time, I suspect one of the cylinders isnt firing properly.
Runs fine and is strong. No oil leaks that I can tell. It does seem to burn about 1 quart per 1500 miles. Other than an annoying rattle when its cold somewhere (i suspect touching the exhaust) it sounds perfect. I don't notice any odd sounds from the engine.
Repairs to the engine I've done include only replacing the coils. The wires, rotor caps, and plugs were replaced about 7000 miles ago and visibly they seem fine (I have not pulled plugs yet). Distributor had ventilation, altho it was stealing it from the brakes (lazy buggers). The AFM connector modifcation was done at some point. AFM is not sticking and seems ok as far as I can tell when pushing on the flap and checking for resitance change. Quite a piece of engineering in that thing; I was scared to even breath on it.
Anything you (Adrian) or anyone else might suggest is greatly appreciated it. I'm thinking of wiring up a switch that will keep the fuel pump on and routing to the inside of the car. Flip it on, drive, and see if the problem remains. Also I think I'm going to invest in another fuel pressure meter. Had one... don't know where it went. /sigh
Location: Mountains of North Carolina, United States.
Car type: 1990 C2, (964 340)
Engine: M6401-62L G5003
Options: C02 158 220 454 494 650
I travel between an elevation of 1300 and 2800 ft. regularly. Lots of ups and downs so this problem is extremely annoying to me. Its still pretty much the same.
Slight downgrades and the problem develops. More severe downgrades and it does not. It also seems to be worse when turning and going slightly down. It acts liek there is no power available. If i back off the throttle it actually gets a tad of power back, like there is enough gas for the idle stage, but nothing else. When it starts to come back it sputters like it was flooded or is just getting gas back into the injectors (I'm not saying it was flooded, it just acts like it. If it was flooded letting it return to idle wouldnt make it suddenly run smooth). It doesnt seem to matter the temperature, humidity, or time of day. It doesnt matter how much fuel is in the tank.
Recently the car has developed another annoyance. It quickly loses power and gets it back. I doubt this is related, but I just mention it because it might be. I am going to try cleaning those connectors again on the afm. It's an instant thing, and I am pretty sure more than 1 cylinder.
Car is unmodified by me and as far as I can tell unmodifed by the previous owner. It was serviced at a dealership with all the papers. The previous owner complained of the same problem to the dealership, but they reported that they were unable to duplicate it.
Well I may as well state this problem as well. Idle is not smooth. It idles steady just above 800, and has never cut off on me. If I didnt know better I'd think it just has a lope from cams. I have a set of plugs to replace when I get the time, I suspect one of the cylinders isnt firing properly.
Runs fine and is strong. No oil leaks that I can tell. It does seem to burn about 1 quart per 1500 miles. Other than an annoying rattle when its cold somewhere (i suspect touching the exhaust) it sounds perfect. I don't notice any odd sounds from the engine.
Repairs to the engine I've done include only replacing the coils. The wires, rotor caps, and plugs were replaced about 7000 miles ago and visibly they seem fine (I have not pulled plugs yet). Distributor had ventilation, altho it was stealing it from the brakes (lazy buggers). The AFM connector modifcation was done at some point. AFM is not sticking and seems ok as far as I can tell when pushing on the flap and checking for resitance change. Quite a piece of engineering in that thing; I was scared to even breath on it.
Anything you (Adrian) or anyone else might suggest is greatly appreciated it. I'm thinking of wiring up a switch that will keep the fuel pump on and routing to the inside of the car. Flip it on, drive, and see if the problem remains. Also I think I'm going to invest in another fuel pressure meter. Had one... don't know where it went. /sigh
04-05-2005, 03:33 AM
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First of all the fuel pump is ON the entire time the engine is running. At no time does it switch off. Fuel over pressure is controlled by routing excess fuel pressure back to the fuel tank.
You didn't purchase this car from Denver by any chance? Your problem seems just like one from Denver last year or the year before.
The standard USA market 964 does not have any altitude correction abilities. This is supposed to be handled by the air flow sensor and the air temperature sensor.
However seeing as your problem is only present when going downhill and not uphill I would suggest you have a mechanical problem.
My first point of call would be the Air flow sensor loom and connector. You need to check if the connector modification has been carried out. A black dot on the connector says the mod has been carried out.
The early 964s had a problem with the way the wires were tied together inside the connector. To cut a long story short the connector pins are under extreme tension from the wires and they come apart.
Unfortunately with these problems it is one step at a time.
What you have to look at is why only downhill. This suggests something is moving out of position when the nose is pointing down. Not when it is pointing up.
Do you have the vacuum operated headlight adjustment? If you do I would be looking for leaks here.
The air box, the air intake are all areas where I would take a look especially for linkages or flapper valves that may be flopping one way. There are not many.
Of course the Bosch Hammer might be useful to detect if you have an engine sensor problem. A failed air temperature sensor failed would certainly cause this problem.
I do not recommend checking the air flow sensor vane by moving it a reliable troubleshooting method. The vane could be flopping open on the run down the hill advising the DME that more air is going in and the DME adjusts the fuel flow and the engine will stumble.
Ciao,
Adrian.
You didn't purchase this car from Denver by any chance? Your problem seems just like one from Denver last year or the year before.
The standard USA market 964 does not have any altitude correction abilities. This is supposed to be handled by the air flow sensor and the air temperature sensor.
However seeing as your problem is only present when going downhill and not uphill I would suggest you have a mechanical problem.
My first point of call would be the Air flow sensor loom and connector. You need to check if the connector modification has been carried out. A black dot on the connector says the mod has been carried out.
The early 964s had a problem with the way the wires were tied together inside the connector. To cut a long story short the connector pins are under extreme tension from the wires and they come apart.
Unfortunately with these problems it is one step at a time.
What you have to look at is why only downhill. This suggests something is moving out of position when the nose is pointing down. Not when it is pointing up.
Do you have the vacuum operated headlight adjustment? If you do I would be looking for leaks here.
The air box, the air intake are all areas where I would take a look especially for linkages or flapper valves that may be flopping one way. There are not many.
Of course the Bosch Hammer might be useful to detect if you have an engine sensor problem. A failed air temperature sensor failed would certainly cause this problem.
I do not recommend checking the air flow sensor vane by moving it a reliable troubleshooting method. The vane could be flopping open on the run down the hill advising the DME that more air is going in and the DME adjusts the fuel flow and the engine will stumble.
Ciao,
Adrian.
04-05-2005, 06:04 AM
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Thought I would add that my UK 964 C4 '90 (53,000mls) has the same issue going downhill.....only occasionally though, happened only a couple of times in my ownership. I havn't owned her for long (3 months) and I've only felt the short 'lack of power' when I have been coasting with no 'right foot pressure', then when I want to accelerate there is a momentary (>2 secs) of no power.
Also, at times get the distinct impression that on a motorway with very little pressure on the accelerator that there is a hesitation when wanting to accelerate? ....don't know if this helps but it is an interesting topic.
Heirsh....you are not alone!
Also, at times get the distinct impression that on a motorway with very little pressure on the accelerator that there is a hesitation when wanting to accelerate? ....don't know if this helps but it is an interesting topic.
Heirsh....you are not alone!
04-05-2005, 07:29 AM
#21
Ryan,
Exactly the same as mine....Do you dip the clutch and pump the gas pedal to clear it ? It has also done it while in heavy slow moving traffic, in second gear. Totally died and had to engage the clutch then disengage to sort of jump start it.
Very annoying, and I must get to the bottom of it.
Cheers,
Mark 90C2
Exactly the same as mine....Do you dip the clutch and pump the gas pedal to clear it ? It has also done it while in heavy slow moving traffic, in second gear. Totally died and had to engage the clutch then disengage to sort of jump start it.
Very annoying, and I must get to the bottom of it.
Cheers,
Mark 90C2
04-05-2005, 09:10 AM
#22
Burning Brakes
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"First of all the fuel pump is ON the entire time the engine is running. At no time does it switch off. Fuel over pressure is controlled by routing excess fuel pressure back to the fuel tank."
Yeah, I was just thinking of verifying this by jumpering it. I was just thinking the dme was tellign ti turn off for some reason, so the only pressure left in the system was the accumulator.
Y"ou didn't purchase this car from Denver by any chance?"
No the car was purchased in North Carolina, Durham area. All the records of work done on it come from a dealer there. I do not recall its purchase location though. I have those records, they are just at home.
"My first point of call would be the Air flow sensor loom and connector."
It was carried out. No black dot though. I pulled it back to check since there wasnt a black dot.
"Do you have the vacuum operated headlight adjustment?"
no
"The air box, the air intake are all areas where I would take a look especially for linkages or flapper valves that may be flopping one way. There are not many.
Of course the Bosch Hammer might be useful to detect if you have an engine sensor problem. A failed air temperature sensor failed would certainly cause this problem."
The AFM works smooth and has, what seems, a good amount of closing force. When the problem was originally mentioned in the repair reports they couldnt find any codes, but that doesnt mean there arent any now.
"I do not recommend checking the air flow sensor vane by moving it a reliable troubleshooting method. The vane could be flopping open on the run down the hill advising the DME that more air is going in and the DME adjusts the fuel flow and the engine will stumble."
Thanks for the help. Sure is an annoying problem.
Yeah, I was just thinking of verifying this by jumpering it. I was just thinking the dme was tellign ti turn off for some reason, so the only pressure left in the system was the accumulator.
Y"ou didn't purchase this car from Denver by any chance?"
No the car was purchased in North Carolina, Durham area. All the records of work done on it come from a dealer there. I do not recall its purchase location though. I have those records, they are just at home.
"My first point of call would be the Air flow sensor loom and connector."
It was carried out. No black dot though. I pulled it back to check since there wasnt a black dot.
"Do you have the vacuum operated headlight adjustment?"
no
"The air box, the air intake are all areas where I would take a look especially for linkages or flapper valves that may be flopping one way. There are not many.
Of course the Bosch Hammer might be useful to detect if you have an engine sensor problem. A failed air temperature sensor failed would certainly cause this problem."
The AFM works smooth and has, what seems, a good amount of closing force. When the problem was originally mentioned in the repair reports they couldnt find any codes, but that doesnt mean there arent any now.
"I do not recommend checking the air flow sensor vane by moving it a reliable troubleshooting method. The vane could be flopping open on the run down the hill advising the DME that more air is going in and the DME adjusts the fuel flow and the engine will stumble."
Thanks for the help. Sure is an annoying problem.
04-05-2005, 11:59 AM
#23
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Have you done anything with the DME relay R41. Mine packed up the other day and for the previous couple of weeks I had noticed some strange intermittant things going on which I put down to the weather, wrong!!!!
Might be worth a look.
I have also seen loose connections on the underside of the relay sockets.
Take a look at the DME to engine harness connectors in the enigne bay relay panel.
A number of people have removed their heat shields (for various reasons) and this has caused damage to these connectors.
The other place to look is under the left seat for damaged wiring in the DME loom.
Intermittant problems like this are normally wiring, connection or leak (air or vacuum) related.
By the way the 964 does not have a fuel accumulator. CIS engines have fuel accumulators. If our understanding of a fuel accumulator is the same.
For the UK 964 owners please advise the option status of your engines. Are they M150? This is critically important because in the UK there are four different basic 964 set up floating around (5 if you include modified).
LHD with catalytic converter and O2 sensor.
RHD with catalytic converter and O2 sensor.
RHD without catalytic converter and O2 sensor with standard M64/01 engine and DME with jumper plugs.
RHD without catalytic converter and O2 sensor with option M150 M64/01 engine with altitude compensation.
All of the above modified to any of the above or somewhere in between.
Ciao,
Adrian.
Might be worth a look.
I have also seen loose connections on the underside of the relay sockets.
Take a look at the DME to engine harness connectors in the enigne bay relay panel.
A number of people have removed their heat shields (for various reasons) and this has caused damage to these connectors.
The other place to look is under the left seat for damaged wiring in the DME loom.
Intermittant problems like this are normally wiring, connection or leak (air or vacuum) related.
By the way the 964 does not have a fuel accumulator. CIS engines have fuel accumulators. If our understanding of a fuel accumulator is the same.
For the UK 964 owners please advise the option status of your engines. Are they M150? This is critically important because in the UK there are four different basic 964 set up floating around (5 if you include modified).
LHD with catalytic converter and O2 sensor.
RHD with catalytic converter and O2 sensor.
RHD without catalytic converter and O2 sensor with standard M64/01 engine and DME with jumper plugs.
RHD without catalytic converter and O2 sensor with option M150 M64/01 engine with altitude compensation.
All of the above modified to any of the above or somewhere in between.
Ciao,
Adrian.
04-05-2005, 12:19 PM
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Dear Ryan and Mark,
Not sure we are talking about the same thing here.
First of all coasting along without the accelerator pressed and with the wheels driving the engine you are going to have a hesitation when you hit the gas.
This is because the DME is a tad confused, it is trying to run in idle fuel schedule (idle microswitch is made) and the ISV is open but the engine rpm is significantly higher than idle.
If you clean the ISV you may find this hesitation time reduced.
By pressing the clutch in you are removing the load from the engine. The rpm will immediately drop but the poor old DME is now pumping too much fuel for the idle schedule and yes stalling can result.
Personally in both these cases I would advise some component cleaning including the fuel injectors before I did anything else.
Might take a peak at the secondary drive belt as well just to be sure.
Ciao,
Adrian.
Not sure we are talking about the same thing here.
First of all coasting along without the accelerator pressed and with the wheels driving the engine you are going to have a hesitation when you hit the gas.
This is because the DME is a tad confused, it is trying to run in idle fuel schedule (idle microswitch is made) and the ISV is open but the engine rpm is significantly higher than idle.
If you clean the ISV you may find this hesitation time reduced.
By pressing the clutch in you are removing the load from the engine. The rpm will immediately drop but the poor old DME is now pumping too much fuel for the idle schedule and yes stalling can result.
Personally in both these cases I would advise some component cleaning including the fuel injectors before I did anything else.
Might take a peak at the secondary drive belt as well just to be sure.
Ciao,
Adrian.
04-05-2005, 12:37 PM
#26
Burning Brakes
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Thanks again Adrian. I will check those things and maybe I'll have some good news.
No fuel accumulator! I am so glad you told me that. I had, up till now, just assumed it had one. Using false information to troubleshoot makes things 10x as bad.
It is a new dme relay. The old one looked fine internally, but as much trouble as everyone has with them I thought I'd try a new one. I think I'll put the old one back in and see if anything changes as putting the new one in didnt help what I was trying to help (turned out to be a coil).
No fuel accumulator! I am so glad you told me that. I had, up till now, just assumed it had one. Using false information to troubleshoot makes things 10x as bad.
It is a new dme relay. The old one looked fine internally, but as much trouble as everyone has with them I thought I'd try a new one. I think I'll put the old one back in and see if anything changes as putting the new one in didnt help what I was trying to help (turned out to be a coil).
05-09-2005, 11:10 AM
#27
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just a followup. I have been tackling other pressing problems lately and havent messed with this much. However, I've done a few things and have a bit more info about my problem.
I fixed the full throttle cam.
I replaced the oxygen sensor.
now...
When this problem occurs I can step on the gas till it triggers wot via the switch and the problem will go away instantly.
It seems like the system adjusts to the high rpm idle via direction from the ox sensor, but takes awhile to compensate when you get back on the throttle, unless you trip wot that causes it to ignore the ox sensor.
I fixed the full throttle cam.
I replaced the oxygen sensor.
now...
When this problem occurs I can step on the gas till it triggers wot via the switch and the problem will go away instantly.
It seems like the system adjusts to the high rpm idle via direction from the ox sensor, but takes awhile to compensate when you get back on the throttle, unless you trip wot that causes it to ignore the ox sensor.
12-23-2005, 10:07 PM
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I don't know if its my imagination, but lately this has been getting worse and severely taking away the joy of driving the car. So I went out for a look today and I think I found the problem.
I was poking around and I found a broken vacuum line. It is t'd off of the left of the throttle body and loops back, down, and finally back foward to what I think is the fuel pressure regulator. It is a device just above the shroud below the throttle bodies. You can't see it unless you shine a light and look in from near the lip of the engine compartment. This could also explain my rich running during hot weather. It broke from oil contamination in/on the u shaped elbow. It looks like it was a slow failure.
I'm not 100% sure this fixed my power loss downhill problem, but I went for 2 drives in areas it has always done it before and not had the problem once. I do notice a very slight hesitation when you get on the gas from letting the car drive the engine, but per Adrian above that is not unusual. It is very very slight, but since I am so sensitive to this problem I notice it (otherwise I would not). So I'm happy.
I guess Santa came a bit early for me.
Or maybe its scrooge playing a joke on me and the next time I drive it it will be back. /shrug
I was poking around and I found a broken vacuum line. It is t'd off of the left of the throttle body and loops back, down, and finally back foward to what I think is the fuel pressure regulator. It is a device just above the shroud below the throttle bodies. You can't see it unless you shine a light and look in from near the lip of the engine compartment. This could also explain my rich running during hot weather. It broke from oil contamination in/on the u shaped elbow. It looks like it was a slow failure.
I'm not 100% sure this fixed my power loss downhill problem, but I went for 2 drives in areas it has always done it before and not had the problem once. I do notice a very slight hesitation when you get on the gas from letting the car drive the engine, but per Adrian above that is not unusual. It is very very slight, but since I am so sensitive to this problem I notice it (otherwise I would not). So I'm happy.
I guess Santa came a bit early for me.
Or maybe its scrooge playing a joke on me and the next time I drive it it will be back. /shrug
