1990 S4 Surging - Barely Running
05-07-2019, 11:09 PM
#16
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I'm with Adamant1971. The intermittent nature points away from a 'mechanical' failure of a part or parts.
In any case, ruling out LH failure is a very good place to start.
In any case, ruling out LH failure is a very good place to start.
05-07-2019, 11:52 PM
#17
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Adam, we should connect and see what our schedules are like.......we've got Mother's Day, I've got appts on Saturday around noon, Elder care on Sunday. If you're available maybe later Saturday afternoon / early evening?
05-08-2019, 12:03 AM
#19
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Remove the carpet covering the brain case.
Unlatch the connectors, rotate away from the ECUs, detach and lay aside the connectors (they are keyed. Nearly impossible to swap on reassembly without a knife.)
Remove two 5mm Alan bolts.
Pull brain case forward a bit
Disconnect coding plug.
Disconnect plug for IMS relay (this is usually tough. If you end up wanting to use a tool between the relay and connector, disconnect the battery first.)
Withdraw brain case.
Remove a bunch of nuts and the cover plate that secures the LH.
Remove LH (it's the big one.)
Best to take a couple of pictures before and during this so that you can route everything back the way it was.
05-08-2019, 02:18 AM
#20
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just pull the whole assy with EZK and take it with you to test. No need to disassemble the LH from the rack/console assy. You'll remove the LH plug from the host and onnect it to your LH leaning on the side of the same rack installed in the host car.
05-08-2019, 02:59 AM
#21
Burning Brakes
why are you guessing at the possible causes without doing any testing ?
Next thing is you are going to be randomly replacing components and if that doesn't work you'll have lost any chance of making a simple diagnosis because you won't know what components to trust.
You clearly have an over-fueling issue so test your fuel pressure first . Over fueling can be due to many things both electronic and mechanical but first put a fuel pressure gauge on the fuel system and check the pressure .
928 atlast made the suggestion that it could be the FPR but you immediately dismissed that even though you hadn't even checked the vacuum line off the FPR for fuel leakage ?
Next thing is you are going to be randomly replacing components and if that doesn't work you'll have lost any chance of making a simple diagnosis because you won't know what components to trust.
You clearly have an over-fueling issue so test your fuel pressure first . Over fueling can be due to many things both electronic and mechanical but first put a fuel pressure gauge on the fuel system and check the pressure .
928 atlast made the suggestion that it could be the FPR but you immediately dismissed that even though you hadn't even checked the vacuum line off the FPR for fuel leakage ?
05-08-2019, 08:15 AM
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True! Just take the whole brain case to the test.
05-08-2019, 01:53 PM
#23
Thanks Dave! Are there any tips or tricks to pulling the LH? I've done the deoxit routine on the CE Panel, haven't messed with the computers yet.
Adam, we should connect and see what our schedules are like.......we've got Mother's Day, I've got appts on Saturday around noon, Elder care on Sunday. If you're available maybe later Saturday afternoon / early evening?
Adam, we should connect and see what our schedules are like.......we've got Mother's Day, I've got appts on Saturday around noon, Elder care on Sunday. If you're available maybe later Saturday afternoon / early evening?
05-08-2019, 10:50 PM
#24
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I had a similar issue a few years ago - car losing power on the highway, then stalled on the off-ramp. I'd restart it, put it in drive, give it throttle and it'd stall. I was able to make it to work by leaving it in drive and coasting in limp mode with no throttle input.
After much reading, I started by cleaning the MAF with some MAF cleaner. Three years later, still no issues.
For the price, something to consider.
After much reading, I started by cleaning the MAF with some MAF cleaner. Three years later, still no issues.
For the price, something to consider.
05-11-2019, 12:35 PM
#25
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Update ......Good news. It's not the LH. Dropped it in Polcan's '88 and it worked fine. Next up it's MAF time.
If it's not that, then I have a real mystery on my hands.......
If it's not that, then I have a real mystery on my hands.......
05-11-2019, 02:59 PM
#26
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Have you done the basic relay-relay-relay and contacts-cleaning yet?
For some reason, shark owners immediately assume the worst when a running symptom appears. While it may easily be the $$$MAF , it can just as easily (and more commonly) be a relay or connection.
A fuel pressure check will help identify whether the problem is between the battery and fuel injection rails. That's the connections, ground, relay, pumps, regulators and dampers. For any funny-runny symptom, this simple test should be high on the list.
MAF failure sometimes happens all at once, but more typically sneaks up on you. The LHA box will compensate for MAF wear by continuously learning the fuel needs via the oxy sensor. At some point the MAF signal falls out of the range in which the LH will operate, and the car will run progressively more poorly.
Meanwhile, the LH includes a "limp mode" function intended to allow you to drive off the autobahn safely on MAF failure. Unplug the MAF to force "limp mode" The car will run rough at idle, and will tolerate a minimum loaded throttle that's sufficient to go 30-40 MPH but not much more. Basically, if the car runs and idles better with the MAF disconnected, you can narrow the problem to the MAF and its connectors and wiring. Tangent: I had an interesting running symptom that pointed to a MAF issue, where the problem turned out to be a bit of waxy something in the connector. A careful cleaning [dis]solved that handily. Cleaning and some contact cleaner like Deoxit help when there are minor corrosion issues in the connector too. The signal voltages are really small, so it doesn't take much contact resistance to drop them out of the useful signal range.
In addition, you may want to use some MAF cleaner spray on the sensor wire in that little venturi nozzle in the middle. MAF needs to be out of the car, and the screen should come out for the cleaning. The little sensor wire gets a high-current "burn-off" treatment every time the engine is shut down. Intent is to carbonize any oil or other contamination that might interfere with the transfer of heat from the thermistor and sensor wire to the air passing through the little nozzle. MAF cleaner can flush that off if the burnoff process isn't enough. Be aware that there are plastic parts there that don't care for the cleaner, so you'll want to spray just the wire and not the nozzle if you can avoid it.
First: relay-relay-relay, connections and grounds. Fuel pressure.
For some reason, shark owners immediately assume the worst when a running symptom appears. While it may easily be the $$$MAF , it can just as easily (and more commonly) be a relay or connection.
A fuel pressure check will help identify whether the problem is between the battery and fuel injection rails. That's the connections, ground, relay, pumps, regulators and dampers. For any funny-runny symptom, this simple test should be high on the list.
MAF failure sometimes happens all at once, but more typically sneaks up on you. The LHA box will compensate for MAF wear by continuously learning the fuel needs via the oxy sensor. At some point the MAF signal falls out of the range in which the LH will operate, and the car will run progressively more poorly.
Meanwhile, the LH includes a "limp mode" function intended to allow you to drive off the autobahn safely on MAF failure. Unplug the MAF to force "limp mode" The car will run rough at idle, and will tolerate a minimum loaded throttle that's sufficient to go 30-40 MPH but not much more. Basically, if the car runs and idles better with the MAF disconnected, you can narrow the problem to the MAF and its connectors and wiring. Tangent: I had an interesting running symptom that pointed to a MAF issue, where the problem turned out to be a bit of waxy something in the connector. A careful cleaning [dis]solved that handily. Cleaning and some contact cleaner like Deoxit help when there are minor corrosion issues in the connector too. The signal voltages are really small, so it doesn't take much contact resistance to drop them out of the useful signal range.
In addition, you may want to use some MAF cleaner spray on the sensor wire in that little venturi nozzle in the middle. MAF needs to be out of the car, and the screen should come out for the cleaning. The little sensor wire gets a high-current "burn-off" treatment every time the engine is shut down. Intent is to carbonize any oil or other contamination that might interfere with the transfer of heat from the thermistor and sensor wire to the air passing through the little nozzle. MAF cleaner can flush that off if the burnoff process isn't enough. Be aware that there are plastic parts there that don't care for the cleaner, so you'll want to spray just the wire and not the nozzle if you can avoid it.
First: relay-relay-relay, connections and grounds. Fuel pressure.
05-11-2019, 03:09 PM
#27
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Thread Starter
Have you done the basic relay-relay-relay and contacts-cleaning yet?
For some reason, shark owners immediately assume the worst when a running symptom appears. While it may easily be the $$$MAF , it can just as easily (and more commonly) be a relay or connection.
A fuel pressure check will help identify whether the problem is between the battery and fuel injection rails. That's the connections, ground, relay, pumps, regulators and dampers. For any funny-runny symptom, this simple test should be high on the list.
MAF failure sometimes happens all at once, but more typically sneaks up on you. The LHA box will compensate for MAF wear by continuously learning the fuel needs via the oxy sensor. At some point the MAF signal falls out of the range in which the LH will operate, and the car will run progressively more poorly.
Meanwhile, the LH includes a "limp mode" function intended to allow you to drive off the autobahn safely on MAF failure. Unplug the MAF to force "limp mode" The car will run rough at idle, and will tolerate a minimum loaded throttle that's sufficient to go 30-40 MPH but not much more. Basically, if the car runs and idles better with the MAF disconnected, you can narrow the problem to the MAF and its connectors and wiring. Tangent: I had an interesting running symptom that pointed to a MAF issue, where the problem turned out to be a bit of waxy something in the connector. A careful cleaning [dis]solved that handily. Cleaning and some contact cleaner like Deoxit help when there are minor corrosion issues in the connector too. The signal voltages are really small, so it doesn't take much contact resistance to drop them out of the useful signal range.
In addition, you may want to use some MAF cleaner spray on the sensor wire in that little venturi nozzle in the middle. MAF needs to be out of the car, and the screen should come out for the cleaning. The little sensor wire gets a high-current "burn-off" treatment every time the engine is shut down. Intent is to carbonize any oil or other contamination that might interfere with the transfer of heat from the thermistor and sensor wire to the air passing through the little nozzle. MAF cleaner can flush that off if the burnoff process isn't enough. Be aware that there are plastic parts there that don't care for the cleaner, so you'll want to spray just the wire and not the nozzle if you can avoid it.
First: relay-relay-relay, connections and grounds. Fuel pressure.
For some reason, shark owners immediately assume the worst when a running symptom appears. While it may easily be the $$$MAF , it can just as easily (and more commonly) be a relay or connection.
A fuel pressure check will help identify whether the problem is between the battery and fuel injection rails. That's the connections, ground, relay, pumps, regulators and dampers. For any funny-runny symptom, this simple test should be high on the list.
MAF failure sometimes happens all at once, but more typically sneaks up on you. The LHA box will compensate for MAF wear by continuously learning the fuel needs via the oxy sensor. At some point the MAF signal falls out of the range in which the LH will operate, and the car will run progressively more poorly.
Meanwhile, the LH includes a "limp mode" function intended to allow you to drive off the autobahn safely on MAF failure. Unplug the MAF to force "limp mode" The car will run rough at idle, and will tolerate a minimum loaded throttle that's sufficient to go 30-40 MPH but not much more. Basically, if the car runs and idles better with the MAF disconnected, you can narrow the problem to the MAF and its connectors and wiring. Tangent: I had an interesting running symptom that pointed to a MAF issue, where the problem turned out to be a bit of waxy something in the connector. A careful cleaning [dis]solved that handily. Cleaning and some contact cleaner like Deoxit help when there are minor corrosion issues in the connector too. The signal voltages are really small, so it doesn't take much contact resistance to drop them out of the useful signal range.
In addition, you may want to use some MAF cleaner spray on the sensor wire in that little venturi nozzle in the middle. MAF needs to be out of the car, and the screen should come out for the cleaning. The little sensor wire gets a high-current "burn-off" treatment every time the engine is shut down. Intent is to carbonize any oil or other contamination that might interfere with the transfer of heat from the thermistor and sensor wire to the air passing through the little nozzle. MAF cleaner can flush that off if the burnoff process isn't enough. Be aware that there are plastic parts there that don't care for the cleaner, so you'll want to spray just the wire and not the nozzle if you can avoid it.
First: relay-relay-relay, connections and grounds. Fuel pressure.
05-11-2019, 07:42 PM
#28
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Thread Starter
Update.......Fuel Pressure is as suspected....solid 60 psi (on my gauge. I think it reads slightly high....been the same through two FPRs.
Disconnected the MAF...car still doesn't want to run under 1,000 rpm...give it fuel, and runs a bit rough but solid at 2,000 - 4,000 rpm.
We're getting there!
Disconnected the MAF...car still doesn't want to run under 1,000 rpm...give it fuel, and runs a bit rough but solid at 2,000 - 4,000 rpm.
We're getting there!
Last edited by 928 at last; 05-11-2019 at 07:43 PM. Reason: Typo
05-12-2019, 09:01 AM
#29
Burning Brakes
Update.......Fuel Pressure is as suspected....solid 60 psi (on my gauge. I think it reads slightly high....been the same through two FPRs.
Disconnected the MAF...car still doesn't want to run under 1,000 rpm...give it fuel, and runs a bit rough but solid at 2,000 - 4,000 rpm.
We're getting there!
Disconnected the MAF...car still doesn't want to run under 1,000 rpm...give it fuel, and runs a bit rough but solid at 2,000 - 4,000 rpm.
We're getting there!
What is anyone supposed to deduce from that ?
60 psi is too high under any conditions but once again you do not tell us anything about how you tested. ?
Was it with the engine running at idle ?
was it with the fuel pump relay bypass fitted ?
Where was the gauge fitted ?
I do not have a 928 anymore so I do not have a manual. Check your manual for the correct recommended specs for your model year and compare .I believe idle pressure with engine running should be 3.3 Bar
If your vacuum system is leaking or not working properly then your FPR will not be able to functioni correctly and will raise the fuel pressure accordingly thinking it is a constant cold start situation.
Last edited by peanut; 05-12-2019 at 03:01 PM.
05-12-2019, 09:38 AM
#30
what the hell does 'SOLID ' mean ? can't we talk in proper English anymore ?
What is anyone supposed to deduce from that ?
60 psi is too high under any conditions but once again you do not tell us anything about how you tested. ?
Was it with the engine running at idle ?
was it with the DME relay bypass fitted ?
Where was the gauge fitted ?
I do not have a 928 anymore so I do not have a manual. Check your manual for the correct recommended specs for your model year and compare .I believe idle pressure with engine running should be 3.3 Bar
If your vacuum system is leaking or not working properly then your FPR will not be able to functioni correctly and will raise the fuel pressure accordingly thinking it is a constant cold start situation.
What is anyone supposed to deduce from that ?
60 psi is too high under any conditions but once again you do not tell us anything about how you tested. ?
Was it with the engine running at idle ?
was it with the DME relay bypass fitted ?
Where was the gauge fitted ?
I do not have a 928 anymore so I do not have a manual. Check your manual for the correct recommended specs for your model year and compare .I believe idle pressure with engine running should be 3.3 Bar
If your vacuum system is leaking or not working properly then your FPR will not be able to functioni correctly and will raise the fuel pressure accordingly thinking it is a constant cold start situation.