88 S4 has started running like a poorly tuned lawn mower
06-14-2011, 01:46 PM
#31
Rennlist Member
Brett, I've subscribed to this thread.... to see what you find out.
With the unidentifiable smoke mine was putting out, I am more than a little concerned to drive it -even though after about 30 minutes of cooldown, it was fine and has been fine.
What would cause an intermittent emergency default to run on half the cylinders and then be fine?
With the unidentifiable smoke mine was putting out, I am more than a little concerned to drive it -even though after about 30 minutes of cooldown, it was fine and has been fine.
What would cause an intermittent emergency default to run on half the cylinders and then be fine?
06-14-2011, 02:45 PM
#32
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So if an twin coil 928 suddenly has only 1/2 the normal power be very careful about cat caused fires....note that some later 928s have had the ignition monitoring system by passed jumpered and will not save the car !
06-15-2011, 09:19 PM
#33
Nordschleife Master
All S4's are LH2.3 (all 87-95 model year 928's). LH2.2 was used in the 84-86 Euro 16V and 85/86 32V 928's.
"General LH going bad" - that would usually be failure of the tile (small daughterboard mounted on the LH mainboard). The tile is the common failure point of the LH, and is the part replaced as part of a rebuild, and handles idle control and the O2 loop. Issues with either of those functions usually provide early indications of impending complete LH failure (once other possible causes like Temp II, O2 sensor etc. are eliminated). Subsequent complete failure of the LH is shown by an inability to run, and often the injectors clicking rapidly with the ignition set to "on" and the engine not running.
MAF voltage too high is extremely unlikely; however, a non-working MAF (i.e. no voltage) will cause the LH to run in "limp home" mode where it uses a fixed-width injector pulse that exhibits very rich running at idle. Limp Home mode will however enable the car to run, hence this case is likely not it.
If not done yet, measuring fuel pressure would be useful.
Cracks in the circuit board would be interesting.
"General LH going bad" - that would usually be failure of the tile (small daughterboard mounted on the LH mainboard). The tile is the common failure point of the LH, and is the part replaced as part of a rebuild, and handles idle control and the O2 loop. Issues with either of those functions usually provide early indications of impending complete LH failure (once other possible causes like Temp II, O2 sensor etc. are eliminated). Subsequent complete failure of the LH is shown by an inability to run, and often the injectors clicking rapidly with the ignition set to "on" and the engine not running.
MAF voltage too high is extremely unlikely; however, a non-working MAF (i.e. no voltage) will cause the LH to run in "limp home" mode where it uses a fixed-width injector pulse that exhibits very rich running at idle. Limp Home mode will however enable the car to run, hence this case is likely not it.
If not done yet, measuring fuel pressure would be useful.
Cracks in the circuit board would be interesting.
I believe LH in an '88 is 2.2, not 2.3.
<snip>
Things that would cause the system to send too much fuel:
1. MAF voltage too high, stuck high, or reading high, or maybe MAF losing signal ground.
2. Fuel pressure too high - bad FPR or vacuum leak at FPR.
3. LH thinks engine is really cold. Sounds like you already eliminated this possibility.
4. Maybe (but I'm not convinced), Lambda overcompensation. Since my '88 runs passably well with the O2 disconnected, I don't think this is the issue. In fact, mine had the O2 disconnected for the first year or so I owned the car, and, other than being a bit rich at startup, it really ran well and plugs looked fine.
5. General LH going bad.
I think that 1, 2, or 5 are most likely here. Have you checked the condition of the MAF plug and wiring? Have you checked for fuel in the vacuum lines to the FPR and dampers? Does the car run any worse with the vacuum line at the FPR disconnected?
<snip>
Things that would cause the system to send too much fuel:
1. MAF voltage too high, stuck high, or reading high, or maybe MAF losing signal ground.
2. Fuel pressure too high - bad FPR or vacuum leak at FPR.
3. LH thinks engine is really cold. Sounds like you already eliminated this possibility.
4. Maybe (but I'm not convinced), Lambda overcompensation. Since my '88 runs passably well with the O2 disconnected, I don't think this is the issue. In fact, mine had the O2 disconnected for the first year or so I owned the car, and, other than being a bit rich at startup, it really ran well and plugs looked fine.
5. General LH going bad.
I think that 1, 2, or 5 are most likely here. Have you checked the condition of the MAF plug and wiring? Have you checked for fuel in the vacuum lines to the FPR and dampers? Does the car run any worse with the vacuum line at the FPR disconnected?
06-15-2011, 09:49 PM
#34
Drifting
Thread Starter
So, I replaced the LH and MAF tonight, as well as replacing the fouled spark plugs with Bosch +4 and changing the oil and filter.
Car fired right up but is still running just as poorly, if not worse. It will not hold idle and returning from acceleration the RPMs bottom out and the car usually dies. It is running very rich, black smoke on hard acceleration and black smoke idling at a stop light. I have to keep the RPMs up at a stop light to keep it from dying. It seems to run pretty well at high RPMs, but at mid RPMs it seems to be missing out.
Very disappointing, to say the least.
Another thing I noticed is that I am losing coolant, but I don't see it under the car anywhere. The exhaust doesn't seem to have any in it, but could a head gasket issue cause these problems?
I'll borrow a fuel pressure gauge this weekend and test the fuel pressure.
I already checked the FPR and FPD for gas smell and vacuum. They all hold vacuum and I don't smell fuel in their lines.
What are my next steps? I'll test the injectors one at a time and then the spark plug wires on at a time, but I don't know if either of those would be the cause here.
Car fired right up but is still running just as poorly, if not worse. It will not hold idle and returning from acceleration the RPMs bottom out and the car usually dies. It is running very rich, black smoke on hard acceleration and black smoke idling at a stop light. I have to keep the RPMs up at a stop light to keep it from dying. It seems to run pretty well at high RPMs, but at mid RPMs it seems to be missing out.
Very disappointing, to say the least.
Another thing I noticed is that I am losing coolant, but I don't see it under the car anywhere. The exhaust doesn't seem to have any in it, but could a head gasket issue cause these problems?
I'll borrow a fuel pressure gauge this weekend and test the fuel pressure.
I already checked the FPR and FPD for gas smell and vacuum. They all hold vacuum and I don't smell fuel in their lines.
What are my next steps? I'll test the injectors one at a time and then the spark plug wires on at a time, but I don't know if either of those would be the cause here.
06-16-2011, 12:46 AM
#35
Rennlist Member
Using Chris's suggestion, I popped the hood and made sure both of my coil wires were fully seated. One was kinked and I just barely moved it.
Got back in the driver's seat and fired it up... it was idling normally. Closed the hood, went to dinner, came home -no stumbling.
I will be replacing the coils and plug wire set in the near future...
06-16-2011, 01:03 AM
#36
Three Wheelin'
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So, I replaced the LH and MAF tonight, as well as replacing the fouled spark plugs with Bosch +4 and changing the oil and filter.
Car fired right up but is still running just as poorly, if not worse. It will not hold idle and returning from acceleration the RPMs bottom out and the car usually dies. It is running very rich, black smoke on hard acceleration and black smoke idling at a stop light. I have to keep the RPMs up at a stop light to keep it from dying. It seems to run pretty well at high RPMs, but at mid RPMs it seems to be missing out.
Very disappointing, to say the least.
Another thing I noticed is that I am losing coolant, but I don't see it under the car anywhere. The exhaust doesn't seem to have any in it, but could a head gasket issue cause these problems?
I'll borrow a fuel pressure gauge this weekend and test the fuel pressure.
I already checked the FPR and FPD for gas smell and vacuum. They all hold vacuum and I don't smell fuel in their lines.
What are my next steps? I'll test the injectors one at a time and then the spark plug wires on at a time, but I don't know if either of those would be the cause here.
Car fired right up but is still running just as poorly, if not worse. It will not hold idle and returning from acceleration the RPMs bottom out and the car usually dies. It is running very rich, black smoke on hard acceleration and black smoke idling at a stop light. I have to keep the RPMs up at a stop light to keep it from dying. It seems to run pretty well at high RPMs, but at mid RPMs it seems to be missing out.
Very disappointing, to say the least.
Another thing I noticed is that I am losing coolant, but I don't see it under the car anywhere. The exhaust doesn't seem to have any in it, but could a head gasket issue cause these problems?
I'll borrow a fuel pressure gauge this weekend and test the fuel pressure.
I already checked the FPR and FPD for gas smell and vacuum. They all hold vacuum and I don't smell fuel in their lines.
What are my next steps? I'll test the injectors one at a time and then the spark plug wires on at a time, but I don't know if either of those would be the cause here.
Last edited by SQLGuy; 06-16-2011 at 01:06 AM. Reason: Correction and more info
06-16-2011, 12:28 PM
#37
Drifting
Thread Starter
I'll check the MAF plug voltage tonight.
I am going to go ahead and replace the FPR, but will test fuel pressure before and after.
So, to understand what I will be seeing, if the fuel pressure is too high, the injectors will spray the fuel that is supplied to them, regardless of what they should be limited to? If I have 19lb injectors and the fuel pressure is normally ~35, is it the job of the dampers to meter that to ~19? If so, and since all 8 of my plugs were fouled, indicating all cylinders are rich, that would lead me to believe either both my dampers are bad, or both are good. Is my logic sound?
If the FPR is bad, could it lead to too much fuel, ie, running rich?
If the dampers are supposed to meter the pressure, then they should compensate for the FPR if its is allowing too high pressure, correct?
I am going to go ahead and replace the FPR, but will test fuel pressure before and after.
So, to understand what I will be seeing, if the fuel pressure is too high, the injectors will spray the fuel that is supplied to them, regardless of what they should be limited to? If I have 19lb injectors and the fuel pressure is normally ~35, is it the job of the dampers to meter that to ~19? If so, and since all 8 of my plugs were fouled, indicating all cylinders are rich, that would lead me to believe either both my dampers are bad, or both are good. Is my logic sound?
If the FPR is bad, could it lead to too much fuel, ie, running rich?
If the dampers are supposed to meter the pressure, then they should compensate for the FPR if its is allowing too high pressure, correct?
06-16-2011, 12:45 PM
#38
Drifting
Thread Starter
Ok, i read up on the functions of the FPR and dampers. It seems the dampers do not affect rate of flow so much, only help steady the stream, countering the pulses from the injectors.
06-16-2011, 01:10 PM
#39
Rennlist Member
If you've checked there's no fuel in the vac laine to FPR and dampers, and you have known good LH and MAf, then get engine upo to temperature, unplug Temp 2 sensor.
Then disconnect battery ground, unplug O2 sensor, reconnect battery and fire it up again. Let us know if any change.
Then disconnect battery ground, unplug O2 sensor, reconnect battery and fire it up again. Let us know if any change.
06-16-2011, 01:19 PM
#40
Even if the boots look good on your MAF and Temp II, cut in to them and look. On more than one occasion, I've taken them apart to find several of the wires were exposed and touching other ones. Don't worry about damaging the boot, when you are finished and things are fine, you can wrap them in silicone tape and they will be fine.
06-16-2011, 01:32 PM
#42
Drifting
Thread Starter
John, reconnect battery and leave Temp II and O2 unplugged?
I will add a visual inspection of temp II and MAF wires to my list for tonight, as well as ensuring I have spark to all cylinders.
I will add a visual inspection of temp II and MAF wires to my list for tonight, as well as ensuring I have spark to all cylinders.
Last edited by Brett Jenkins; 06-16-2011 at 03:14 PM.
06-16-2011, 03:13 PM
#43
Rennlist Member
Can a regular (American musclecar) type of canister coil be used on the dual-coil S4 system (Mallory, Accel, MSD)?
These are obviously more readily available and lower priced... any thoughts, Alan?
These are obviously more readily available and lower priced... any thoughts, Alan?
06-16-2011, 03:32 PM
#44
Official Bay Area Patriot
Fuse 24 Assassin
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Fuse 24 Assassin
Rennlist Member
How does the LH ground look under the fuel dampener (or is it the regulator) on the passenger rear of the engine block? My symptoms were virtually identical to yours until I cleaned this up.
Also, how does your MAF harness look? Any frayed wiring?
Also, how does your MAF harness look? Any frayed wiring?
06-16-2011, 03:40 PM
#45
Official Bay Area Patriot
Fuse 24 Assassin
Rennlist Member
Fuse 24 Assassin
Rennlist Member
Brett,
Here is a link to one of my posts in a thread I started. If you wish to read through it, you can see I had numerous running issues and did my best to cover every base possible to fix them. After the grounds MPVIII and MPIX were cleaned at the back of the engine and MAF harness repaired, the car ran like it was new. Now, I have an ignition switch I need to order to fix some gremlins and a sputtering car on a cold start.
https://rennlist.com/forums/7612340-post140.html
Here is a link to one of my posts in a thread I started. If you wish to read through it, you can see I had numerous running issues and did my best to cover every base possible to fix them. After the grounds MPVIII and MPIX were cleaned at the back of the engine and MAF harness repaired, the car ran like it was new. Now, I have an ignition switch I need to order to fix some gremlins and a sputtering car on a cold start.
https://rennlist.com/forums/7612340-post140.html