79 928 Starts okay and then dies. Car runs rich and will not hold an idle
09-02-2008, 02:02 PM
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79 928 Starts okay and then dies. Car runs rich and will not hold an idle
I have a 1979 928 that had a lot of fuel problems. I cleaned out gas tank, replaced fuel pump, replaced fuel accumulator, replaced fuel filter, cleaned injectors, and replaced fuel distributor. I cleaned the warm up regulator but did not replace it.
I also replaced the plug wires, and spark plugs. The plugs show that the car runs very rich.
The car starts fine and runs at 1600 RPM or so. After a couple of minutes, the idle drops and the car dies. The car will start again but then it will not hold an idle around 800-1000 rpm-it just dies. I adjusted the throttle adjustment screw and it did not affect the idle (closed the adjustment screw and then opened it up two revolutions. I notice that in front of the fuel distributor there is a spring loaded device. When I push down on it, the car idles fine and when I let off on it the car dies. It is like when I let air into the system the the mixtures is not as rich.
This symptom reminds me of the old cars when you first start it up with the choke on, the car runs fine. Then when you take the choke off the car dies.
Any ideas??
I also replaced the plug wires, and spark plugs. The plugs show that the car runs very rich.
The car starts fine and runs at 1600 RPM or so. After a couple of minutes, the idle drops and the car dies. The car will start again but then it will not hold an idle around 800-1000 rpm-it just dies. I adjusted the throttle adjustment screw and it did not affect the idle (closed the adjustment screw and then opened it up two revolutions. I notice that in front of the fuel distributor there is a spring loaded device. When I push down on it, the car idles fine and when I let off on it the car dies. It is like when I let air into the system the the mixtures is not as rich.
This symptom reminds me of the old cars when you first start it up with the choke on, the car runs fine. Then when you take the choke off the car dies.
Any ideas??
09-02-2008, 02:30 PM
#2
The spring loaded device is the A/F mixture adjustment. If you just push it down, it slightly opens the air sensor plate. The intake vacuum should be opening the plate unless it is sticking. Make sure it is properly centered and doesn't touch the air horn when at rest. If that is OK, check for vacuum leaks as those can reduce the air movement past the sensor plate. If no vacuum leaks, then try adjusting the A/F mixture slightly to lean. This take a 3mm allen wrench which is placed in the device you noticed. If you gently push down and turn, the device should slip into another recess and you are ready to adjust. Turning CC will lean the mixture. The adjustment is very sensitive and should only be accomplished AFTER everything else is checked out.
Dennis
Dennis
09-02-2008, 02:49 PM
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Dennis: Thank you for the leads. I know what the A/F mixture adjustment is. Just to be perfectly clear, when I put back the air filter, air housing etc, I should still be able to push it down through the air housing. In other words, there are no hoses or anything like that attached to it.
I am still learning about this problem and I do not understand all the terms yet. Exactly what do you mean by the "intake vacuum." Is it a hose that I should be looking for. Second, what is an "air horn."
Gary
I am still learning about this problem and I do not understand all the terms yet. Exactly what do you mean by the "intake vacuum." Is it a hose that I should be looking for. Second, what is an "air horn."
Gary
09-02-2008, 03:33 PM
#4
Intake vacuum is the normal suction created by the intake stroke of the piston. This suction/vacuum should open the air sensor plate which adjusts the flow of fuel to the injectors. If you have a vacuum leak upstream of the sensor the engine will starve for air and the A/F mixture will be off.
BTW it is a LOT easier to adjust the A/F mixture with the filter housing off.
Dennis
BTW it is a LOT easier to adjust the A/F mixture with the filter housing off.
Dennis
09-02-2008, 03:46 PM
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Dennis: Yep, I have been working with the air housing off. I just thought that I missing something. But getting back to my first question, the car seems to run fine (more or less) until it warms up after a couple of minutes. So, the vacuum leak exists regardless of whether the engine is cold or hot. What don't I get here?
Thank you again.
Gary
Thank you again.
Gary
09-02-2008, 05:46 PM
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The warmup regulator is actually the control pressure regulator and it is what sets the mixture ALL THE TIME it is the brains of a brainless fuel injection system....
09-02-2008, 06:03 PM
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It sounds like your car is running on the cold start circuit only. The cold start is a single injector that is electrically fired. You shouldn't mess with the throttle adjustment screw just yet.
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09-02-2008, 06:19 PM
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The cold start injector works with an air(throttle plate) bypass valve. When working on your car, start with a cold engine. Observe the big air metering plate which lets air into the fuel distributor head. During cold operation, the air metering plate should be nearly closed, and the throttle bypass valve should be open, supplying aux air for the cold start injector to run the engine at a richer mixture than normal.
Once the temperature sense reaches a certain value, the cold start injector is closed, and the air bypass valve should also close. At this time, the car switches over to the air metering plate and the normal injectors in the intakes. When the throttle is pushed down when the engine is cold, the air metering plate will open with the throttle, and the injectors will begin to fire.
If you know where the A/F mixure screw is, you can try adjusting that clockwise just a bit while the car is cold. You will be making the engine run richer, so be very cautious. Some who know me know that I use a can of carb cleaner to keep the engine running just barely while I adjust the mixture. Have a fire extinguisher handy, as they often backfire a bit.
Check carefully for vacuum leaks at the boots around the spider, and also all the hoses leading to the manifold. It's common to find several vacuum leaks on older cars.
Put your location in your signature line and we'll prolly have some one near that can help in person.
Once the temperature sense reaches a certain value, the cold start injector is closed, and the air bypass valve should also close. At this time, the car switches over to the air metering plate and the normal injectors in the intakes. When the throttle is pushed down when the engine is cold, the air metering plate will open with the throttle, and the injectors will begin to fire.
If you know where the A/F mixure screw is, you can try adjusting that clockwise just a bit while the car is cold. You will be making the engine run richer, so be very cautious. Some who know me know that I use a can of carb cleaner to keep the engine running just barely while I adjust the mixture. Have a fire extinguisher handy, as they often backfire a bit.
Check carefully for vacuum leaks at the boots around the spider, and also all the hoses leading to the manifold. It's common to find several vacuum leaks on older cars.
Put your location in your signature line and we'll prolly have some one near that can help in person.
09-02-2008, 08:38 PM
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Jim Bailey and I just talked on the phone and he did a great job of explaining to me how the circuit works vis a vis the warm up regulator. I do not have the tools to check the pressures on the warm up regulator. Does anyone know of a poor-mans way of checking the pressures so that I do not have to buy a rebuilt one or a set of gauges.
The car is not tagged and it will not go very far on its own so I can't take it to somebody to fix.
The car is not tagged and it will not go very far on its own so I can't take it to somebody to fix.
09-02-2008, 10:08 PM
#10
Aaahhhh.. sounds like my life last fall right about this time in fact. ;-)
Been there done that. Having not had a tool myself when it happened to me it is a bit more work as there is a process of trial,error, and exclusion. Since you put a new fuel distributor in.. I say assume its working fine. that leaves only two other components that can richen the mixture, the warm up regulator and the cold start valve. In my case a cold start valve was leaking (drip,drip,drip) making things way too rich. I replaced it with a used unit and then replaced it with a brand new one.
I'll see if I can find the used one.. it should work fine and I can send it to you for testing if you'd like.... just PM me.
I will say though that when I put a new fuel distributor on the car I had to adjust the mixture on mine. each is tuned to its own car. I had to lean it out a bit (turn the mixture screw on the fuel distributor counterclockwise) to make things work to my satisfaction. This involved turning this out, then turning the idle adjust screw a tad to compensate, etc. Fiddle fiddle fiddle until it ran nice and clean. The key was knowing that all my engine rubber intake seals (between the aluminum intake parts) were good and the warm up regulator and cold start valve were in good shape.
Its frustrating my friend.. but just eliminate reasons why it can't work and then adjust the fuel distributor 1/16th of a turn at a time.
Once you get it the car will be sweet. :-)
Curt
-----------------------
79 5sp silver/blk
02 boxster blk/blk
Been there done that. Having not had a tool myself when it happened to me it is a bit more work as there is a process of trial,error, and exclusion. Since you put a new fuel distributor in.. I say assume its working fine. that leaves only two other components that can richen the mixture, the warm up regulator and the cold start valve. In my case a cold start valve was leaking (drip,drip,drip) making things way too rich. I replaced it with a used unit and then replaced it with a brand new one.
I'll see if I can find the used one.. it should work fine and I can send it to you for testing if you'd like.... just PM me.
I will say though that when I put a new fuel distributor on the car I had to adjust the mixture on mine. each is tuned to its own car. I had to lean it out a bit (turn the mixture screw on the fuel distributor counterclockwise) to make things work to my satisfaction. This involved turning this out, then turning the idle adjust screw a tad to compensate, etc. Fiddle fiddle fiddle until it ran nice and clean. The key was knowing that all my engine rubber intake seals (between the aluminum intake parts) were good and the warm up regulator and cold start valve were in good shape.
Its frustrating my friend.. but just eliminate reasons why it can't work and then adjust the fuel distributor 1/16th of a turn at a time.
Once you get it the car will be sweet. :-)
Curt
-----------------------
79 5sp silver/blk
02 boxster blk/blk
09-02-2008, 11:18 PM
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I did not see where it mentions a new fuel distributor. If so, the mixture will need to be adjusted. A set of gauges will be needed if you want to do all the pressure tests. By the time you find the fittings, lines, gauges you'll be better off just buying a set for the CIS.
http://www.autorepairmanuals.biz/sit...uct/STRTU447PB
Then you can loan them out to others!
I still think the fastest way is to use a can of carb cleaner until you get the mixture set close. A slightly more elegant solution is to remove one of the injectors from the intake, reconnect it to the fuel line from the distributor. Then, jumper the fuel pump relay so the pump is running and adjust the 3mm mixture screw until the injector just starts to spritz into a baby food jar. At that point, you can start the car, and move the screw back a bit to keep it running. You need to get it close visually before starting the car.
Remember, fire extinguisher handy.
http://www.autorepairmanuals.biz/sit...uct/STRTU447PB
Then you can loan them out to others!
I still think the fastest way is to use a can of carb cleaner until you get the mixture set close. A slightly more elegant solution is to remove one of the injectors from the intake, reconnect it to the fuel line from the distributor. Then, jumper the fuel pump relay so the pump is running and adjust the 3mm mixture screw until the injector just starts to spritz into a baby food jar. At that point, you can start the car, and move the screw back a bit to keep it running. You need to get it close visually before starting the car.
Remember, fire extinguisher handy.
09-03-2008, 12:01 AM
#12
The cold start injector works with an air(throttle plate) bypass valve. When working on your car, start with a cold engine. Observe the big air metering plate which lets air into the fuel distributor head. During cold operation, the air metering plate should be nearly closed, and the throttle bypass valve should be open, supplying aux air for the cold start injector to run the engine at a richer mixture than normal.
Once the temperature sense reaches a certain value, the cold start injector is closed, and the air bypass valve should also close. At this time, the car switches over to the air metering plate and the normal injectors in the intakes. When the throttle is pushed down when the engine is cold, the air metering plate will open with the throttle, and the injectors will begin to fire.
If you know where the A/F mixure screw is, you can try adjusting that clockwise just a bit while the car is cold. You will be making the engine run richer, so be very cautious. Some who know me know that I use a can of carb cleaner to keep the engine running just barely while I adjust the mixture. Have a fire extinguisher handy, as they often backfire a bit.
Check carefully for vacuum leaks at the boots around the spider, and also all the hoses leading to the manifold. It's common to find several vacuum leaks on older cars.
Put your location in your signature line and we'll prolly have some one near that can help in person.
Once the temperature sense reaches a certain value, the cold start injector is closed, and the air bypass valve should also close. At this time, the car switches over to the air metering plate and the normal injectors in the intakes. When the throttle is pushed down when the engine is cold, the air metering plate will open with the throttle, and the injectors will begin to fire.
If you know where the A/F mixure screw is, you can try adjusting that clockwise just a bit while the car is cold. You will be making the engine run richer, so be very cautious. Some who know me know that I use a can of carb cleaner to keep the engine running just barely while I adjust the mixture. Have a fire extinguisher handy, as they often backfire a bit.
Check carefully for vacuum leaks at the boots around the spider, and also all the hoses leading to the manifold. It's common to find several vacuum leaks on older cars.
Put your location in your signature line and we'll prolly have some one near that can help in person.
It's not an air bypass valve, it is an auxillary air valve. It provides extra air ,bypassing the throttle plate (not the air sensor plate) when the engine is cold.
The cold start valve is powered through the thermotime switch but, since it is on the 50 circuit, it is only powered during cranking, not when the engine is running.
In his earlier post he said the plugs were wet and running rich so why would you have him turn the A/F mixture clockwise to richen it more?
Using carb cleaner to keep an engine running while adjusting the A/F mixture doesn't make sense and runs a big risk of causing a backfire. i.e. more vacuum leaks. There are much easier and safer ways to adjust the A/F mixture on the 928.
Dennis
09-03-2008, 12:08 AM
#13
Jim Bailey and I just talked on the phone and he did a great job of explaining to me how the circuit works vis a vis the warm up regulator. I do not have the tools to check the pressures on the warm up regulator. Does anyone know of a poor-mans way of checking the pressures so that I do not have to buy a rebuilt one or a set of gauges.
The car is not tagged and it will not go very far on its own so I can't take it to somebody to fix.
The car is not tagged and it will not go very far on its own so I can't take it to somebody to fix.
Dennis
09-03-2008, 12:33 AM
#14
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Doc,
It's not an air bypass valve, it is an auxillary air valve. It provides extra air ,bypassing the throttle plate (not the air sensor plate) when the engine is cold.
The cold start valve is powered through the thermotime switch but, since it is on the 50 circuit, it is only powered during cranking, not when the engine is running.
In his earlier post he said the plugs were wet and running rich so why would you have him turn the A/F mixture clockwise to richen it more?
Using carb cleaner to keep an engine running while adjusting the A/F mixture doesn't make sense and runs a big risk of causing a backfire. i.e. more vacuum leaks. There are much easier and safer ways to adjust the A/F mixture on the 928.
Dennis
It's not an air bypass valve, it is an auxillary air valve. It provides extra air ,bypassing the throttle plate (not the air sensor plate) when the engine is cold.
The cold start valve is powered through the thermotime switch but, since it is on the 50 circuit, it is only powered during cranking, not when the engine is running.
In his earlier post he said the plugs were wet and running rich so why would you have him turn the A/F mixture clockwise to richen it more?
Using carb cleaner to keep an engine running while adjusting the A/F mixture doesn't make sense and runs a big risk of causing a backfire. i.e. more vacuum leaks. There are much easier and safer ways to adjust the A/F mixture on the 928.
Dennis
The last sentence, explains how to check the F/A ratio the right way, and I also advised him to have an extinguisher handy just in case. If it's too rich, he'll know if the injector is running when jumping the fuel pump relay and adjust accordingly. I've used the carb cleaner method with good effect just as described in my text to find the right range of setting for the CIS A/F screw. It can be a challenge.
I prefer to start from the lean side, but it's hard to trust the condition of plugs on a car that's been running so short. The fact that in the first post, in the middle of the paragraph he describes pushing down on the spring, and getting the car to idle. It sounds like it may be lean, or rich at various times. Again the best way is to pull an injector, run the pump, adjust the F/A, and then put it back together. Adjust as needed. Using carb cleaner isn't the best way, but it's one way.
Now, I have a question. Why is there a thermo time valve in the circuit of the starter pick to energize the cold start injector?
09-03-2008, 09:29 AM
#15
Doc,
You said
"Once the temperature sense reaches a certain value, the cold start injector is closed, and the air bypass valve should also close. At this time, the car switches over to the air metering plate and the normal injectors in the intakes."
Air ALWAYS goes past the metering/air sensor plate. There is no switch over as you state above. Also, when cold all the injectors are spraying so there is no switch over on them either.
Concerning the carb cleaner. 1. Most carb cleaners have acetone or methylene chloride as a component which can be harmful to some rubber components and paint and 2. The A/F mixture is already within "range" or it wouldn't start at all. And 3 using any starting agent (ether, throttlebody cleaner, carb cleaner) increases the risk of a backfire and blowing out vacuum lines and gaskets. The gasket between the 2 halves of the lower chamber is especially prone to blow out as it is spring secured.
The thermotime switch is there to cut off fuel to the CSV when the engine is warm and to prevent flooding of the engine during long cranking without the engine starting. It is powered by the 50 circuit which is only activated during cranking.
Dennis
You said
"Once the temperature sense reaches a certain value, the cold start injector is closed, and the air bypass valve should also close. At this time, the car switches over to the air metering plate and the normal injectors in the intakes."
Air ALWAYS goes past the metering/air sensor plate. There is no switch over as you state above. Also, when cold all the injectors are spraying so there is no switch over on them either.
Concerning the carb cleaner. 1. Most carb cleaners have acetone or methylene chloride as a component which can be harmful to some rubber components and paint and 2. The A/F mixture is already within "range" or it wouldn't start at all. And 3 using any starting agent (ether, throttlebody cleaner, carb cleaner) increases the risk of a backfire and blowing out vacuum lines and gaskets. The gasket between the 2 halves of the lower chamber is especially prone to blow out as it is spring secured.
The thermotime switch is there to cut off fuel to the CSV when the engine is warm and to prevent flooding of the engine during long cranking without the engine starting. It is powered by the 50 circuit which is only activated during cranking.
Dennis