'98 V70 GLT Intermittent Surging/"Coughing"

[bmdubya1198]

Ahhh.... M54 CCVs... those are fun to do...
Anyway, I swapped the fuel pressure regulator yesterday. I got lucky and found one at the junkyard on a 1997 850 GLT, same setup as mine believe it or not. FPR setups are weird in these cars... and the regulator for the '98 is hard to find anywhere new. I also grabbed the fuel pump relay off that car since it was in great shape, a like-new KAE relay.
I drove the car a little bit today, and it coughed again. So I came back and swapped the relay. Drove it for probably 5 minutes, did it again. However these times were while I was moving, not leaving an intersection.
I've got no idea at this point... unless my fuel pump is slowly dying or something like that. I need a way to monitor or log fuel pressure during a drive so I can see what happens when it does that. I need to check if Torque can do that.

[bmdubya1198]

I'm leaning more and more towards the fuel pump. I was just driving the car a little bit ago, and while cruising I suddenly began to lose power, almost stalled, and it went right back to where it was. Seemed like a very quick gradual loss of fuel.
I'll probably be ordering a fuel pump within the next few days. I don't want to have this car down too long, and I certainly don't want it to leave me stranded.

[bmdubya1198]

Drove the car today and experienced LOTS of little surges, and it was really concerning me. Finally, it bucked really bad and threw some codes and a check engine light. Kind of a relief that I actually got a light.
The codes are as follows...
P0335- Crankshaft position sensor A circuit
P0300- Random/multiple cylinder misfire
P0302- Cylinder 2 misfire
P0303- Cylinder 3 misfire

All codes show as "pending" except P0335, which is current.
I checked the resistance on my crankshaft position sensor, and I got 326 ohms, which is within acceptable range. I cleaned the terminals on the connectors, plugged it back in, and it's running even worse. I tried to hold the idle around 1,500 for a second just to test it, and one of the times I was doing that, the engine sputtered. The first time I started it, everything seemed normal. After I turned the car off, I started it again and it sounded off. It wasn't a slow start, but it didn't actually start as fast (or smooth) as it usually does.
Could my crank sensor be bad even if the resistance is good? This is really making me mad now. I've got my cousin's truck on my driveway because he drove it here and now it has multiple misfires and it won't even start now, my dad's car which is still misfiring, now it's my Volvo's turn to give me problems and misfire. I hate having 3 poorly or non-running cars on my driveway...

[abscate]

Feel for you. I had a week in December I had 4/5 of the fleet down and I was elbow deep in the lean running code on the M54 with SWMBO business trip coming up.

The good it did was it finally forced me to learn Fuel trim measurements and diagnosing

[bmdubya1198]

The fuel trim can be very useful. You just have to know where it should be. The freeze frame on the codes showed mine was at 1.26% or something like that. With that I assume my fuel pump is perfectly fine.
Even with the resistance in acceptable range, I think I'm still going to change this crank sensor. It makes no sense why the car would be running like this if the sensor is good. Going by other people who have had bad CKP sensors, my car is having the same sputtering issue except for me it's happening very often at this point, rather than just cruising at highway speeds.

[abscate]

That 50s guy on Bimmerfest has a great video on fuel trim diagnosing...I shameless stole his video in text form below, but its exactly what progressed on the recent M54 fix. I saved ordering/returning the MAF based on this, and even better, finished the job 3 days earlier and $350 richer. When the lean code came back I almost caved and said it had to be MAF as well as intake boot, but 3 minutes with fuel trim told me I still had a leak and the MAF was fine.

If your scanner supports LIVE DATA you are in luck

The SHORT TERM FUEL TRIM (STFT( is the parameter that tells you how much fuel the ECU is adding to the mix to make the correct mixture.

The ECU in theory only needs the MAF, since that measures the air directly, ergo the ECU knows how much fuel to send to the injectors (more correctly, how long to open the injectors)

But, the upstream OXS sends a signal back to the ECU telling it how much or little oxygen remains in the exhaust - ergo how close the ECU is to the right ratio.

The STFT is the amount extra/less the ECU adds/subtracts to satisfy the OXS measurement. When everything is right it will float around +-10, no more or less and be within a few percent of 0 at steady idle or steady throttle.

Now we get a vacuum leak. Too much air means the ECU has to dump in fuel. Your car runs well, because the mix is still correct!! BUT...STFT runs up to say, 20% Most cars, at 20% or more, then trip a P0171/4 lean code. (This is isn't exactly correct, but you get the idea)

Heres the trick. At idle, a small vacuum leak is a large amount of extra air relative to the closed throttle, so STFT runs up to 20%

Now we open the throttle plate to 2500 rpm. The vacuum leak is now small compared to the air going through the engine, so the air fuel balance is closer and needs less correction, so STFT drops down below 10%

So, monitor STFT at idle. If it sits near 0%, probably no vacuum leak. If its 10-20%, carry on...

Bring revs up to 2500 rpm, if the STFT falls, you confirm a leak

[bmdubya1198]

That 50s guy on Bimmerfest has a great video on fuel trim diagnosing...I shameless stole his video in text form below, but its exactly what progressed on the recent M54 fix. I saved ordering/returning the MAF based on this, and even better, finished the job 3 days earlier and $350 richer. When the lean code came back I almost caved and said it had to be MAF as well as intake boot, but 3 minutes with fuel trim told me I still had a leak and the MAF was fine.

If your scanner supports LIVE DATA you are in luck

The SHORT TERM FUEL TRIM (STFT( is the parameter that tells you how much fuel the ECU is adding to the mix to make the correct mixture.

The ECU in theory only needs the MAF, since that measures the air directly, ergo the ECU knows how much fuel to send to the injectors (more correctly, how long to open the injectors)

But, the upstream OXS sends a signal back to the ECU telling it how much or little oxygen remains in the exhaust - ergo how close the ECU is to the right ratio.

The STFT is the amount extra/less the ECU adds/subtracts to satisfy the OXS measurement. When everything is right it will float around +-10, no more or less and be within a few percent of 0 at steady idle or steady throttle.

Now we get a vacuum leak. Too much air means the ECU has to dump in fuel. Your car runs well, because the mix is still correct!! BUT...STFT runs up to say, 20% Most cars, at 20% or more, then trip a P0171/4 lean code. (This is isn't exactly correct, but you get the idea)

Heres the trick. At idle, a small vacuum leak is a large amount of extra air relative to the closed throttle, so STFT runs up to 20%

Now we open the throttle plate to 2500 rpm. The vacuum leak is now small compared to the air going through the engine, so the air fuel balance is closer and needs less correction, so STFT drops down below 10%

So, monitor STFT at idle. If it sits near 0%, probably no vacuum leak. If its 10-20%, carry on...

Bring revs up to 2500 rpm, if the STFT falls, you confirm a leak

Good info there. That answers my question about a vacuum leak on the E39... there isn't one. Same for the V70... they sit around 1-2%.

[abscate]

Have you setup and monitored fuel pressure during running yet? Looked up thread but did not see that

[sleddriver]

I checked the resistance on my crankshaft position sensor, and I got 326 ohms, which is within acceptable range. I cleaned the terminals on the connectors, plugged it back in, and it's running even worse. I tried to hold the idle around 1,500 for a second just to test it, and one of the times I was doing that, the engine sputtered.....Could my crank sensor be bad even if the resistance is good

Your crank sensor wiring harness & connectors could be shot. Same with the camshaft position sensor wiring harness & connector. They both live a hot, hard life given their location. Same with the ECT sensor wiring & connector. The insulation was peeling off of mine + I had to completely redo the connector.

If you plugged it back in and it's running worse, your on the right track. If the untinned copper is green, you need to rebuild the connector & harness. Also, poor placement of these two critical connectors & wiring harnesses near the coil wire can really cause poor running problems.

[bmdubya1198]

Have you setup and monitored fuel pressure during running yet? Looked up thread but did not see that

I have not. Torque can't get a sensor for it and I don't have a fuel pressure gauge.

I checked the resistance on my crankshaft position sensor, and I got 326 ohms, which is within acceptable range. I cleaned the terminals on the connectors, plugged it back in, and it's running even worse. I tried to hold the idle around 1,500 for a second just to test it, and one of the times I was doing that, the engine sputtered.....Could my crank sensor be bad even if the resistance is good

Your crank sensor wiring harness & connectors could be shot. Same with the camshaft position sensor wiring harness & connector. They both live a hot, hard life given their location. Same with the ECT sensor wiring & connector. The insulation was peeling off of mine + I had to completely redo the connector.

If you plugged it back in and it's running worse, your on the right track. If the untinned copper is green, you need to rebuild the connector & harness. Also, poor placement of these two critical connectors & wiring harnesses near the coil wire can really cause poor running problems.

The black insulation that surrounds the wires for the sensor is broken in one section where it bends over a bracket. The wires are in tact, but the wear through the insulation was suspicious. I heard about the wire needing to be away from the ignition wires, and I zip tied the harness out of the way (it was touching the coil wire) and it ran just as bad.
When you say the harness could be bad, do you mean the harness/wires attached to the sensor, or the harness where the sensor connects? I'm sure it's possible for the harness (https://www.napaonline.com/napa/en/p/CR ... 0232402558) to be bad. The connectors had nasty caked up grease in them, I assume it was ancient dielectric grease. I tried to clean that out when I saw it.