940 Rough idle, fuel pressure issue?

bmdubya1198 said:

Yes, I?m aware. I checked the diagrams after checking it.

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curious to see how it develops, good luck

I'm really hoping this O2 sensor fixes it once and for all, it would make sense that it's been failing for a while. It shouldn't be running so rich when revving though. My plugs certainly don't look like it's running as rich as the O2 sensor shows.

Check your wiring between the LH and the O2 also, while you're at it.

shoestring said:

Check your wiring between the LH and the O2 also, while you're at it.

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Will do!

On the off chance I'm being dumb, use the obd to cycle the injectors and give a listen w the screwdriver at the base of each one.

Marty

oleseahorse said:

On the off chance I'm being dumb, use the obd to cycle the injectors and give a listen w the screwdriver at the base of each one.

Marty

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I did, they are all clicking the same. None sound weaker and they all 4 work.

No surprise, the new O2 sensor didn't fix it. Great!

I tried unplugging the large vacuum hose that goes to the climate control (just to make sure there aren't any leaks in that area) and after capping it off, it started kinda hard and the CEL came on for a few seconds. Weird. Anyway, I'm not sure what to do next... this car has really been testing my abilities. I've never had such a hard time diagnosing a seemingly simple problem.
I'm about to pull the cam cover now and swap out the valve shim on the cylinder 1 exhaust valve. That should loosen up the clearance to match up with the rest of them. I should have done that before, but oh well... at least it's easy to access.

bmdubya1198 said:

No surprise, the new O2 sensor didn't fix it. Great!

I tried unplugging the large vacuum hose that goes to the climate control (just to make sure there aren't any leaks in that area) and after capping it off, it started kinda hard and the CEL came on for a few seconds. Weird. Anyway, I'm not sure what to do next... this car has really been testing my abilities. I've never had such a hard time diagnosing a seemingly simple problem.
I'm about to pull the cam cover now and swap out the valve shim on the cylinder 1 exhaust valve. That should loosen up the clearance to match up with the rest of them. I should have done that before, but oh well... at least it's easy to access.

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Have you done a voltage test of new o2 at normal operating temperature(do not waste time checking cold) ? It's important to verify which systems are working properly.

Otto Mattik said:

Have you done a voltage test of new o2 at normal operating temperature(do not waste time checking cold) ? It's important to verify which systems are working properly.

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I'll test this today. I went ahead and adjusted the valve clearance on the #1 exhaust valve, and it was definitely WAY too tight (0.010").

Looked over the voltage at each pin on the ECU just out of curiosity, and most everything looks good. Just had a couple concerns...

Pin 5 was the most concerning. It's a signal ground, and it should have battery voltage with the key on and engine off. My car is showing 37.6 mV... that's a bit low. Typo maybe, or is this supposed to be 12v?
Pin 18 (injector control) should be battery voltage key on engine off, and only 190-200 mV engine on. It's showing battery voltage at idle. The pinout says when engine speed increases, the signal should as well. It goes down when I rev it. Again, maybe it's different for my '91 turbo, but worth mentioning.
Pin 25 (load signal) was a little high with the key on, engine off at 350 mV. It shows 250-300 mV.
Pin 32 is low (32 mV, should be 12v), but I have the cold start injector unplugged so I'm not worried about that one.

Today when I started the car, it ran like absolute garbage. Even worse than before... it has a hard time starting now before idle "normalizes" (relative term with this car). CEL actually comes on for a few seconds, then turns off. Really odd. I'll have to check for codes tomorrow just in case it stored anything.
I also checked the O2 sensor signal at the ECU, and it started around 0.5V (engine was warm earlier in the day, but it had been sitting for a few hours) then slowly went up as I ran it longer. By the time I went on to test other pins, it was around 0.7V.

This is the pinout I referenced: https://ipdown.net/jetronic.info/tiki-index.php?page=LH2.4+Pinouts+and+Diagrams

If, after warm up, the O2 sensor is not swinging something upstream has failed. The engine is running RICH. Now, what would cause that?

TestPoint said:

If, after warm up, the O2 sensor is not swinging something upstream has failed. The engine is running RICH. Now, what would cause that?

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Yeah, I'm pretty sure it's running rich. I'll have to get it to operating temperature and check once again just to be sure, but just from how it smells, it's running rich.

Put some dish soap around each joint in the exhaust system upstream of the O2 sensor, and blow air through the tailpipe with a shop vac's exhaust port. You might have an exhaust leak bathing your O2 sensor in fresh air. Are you sure there isn't a huge gash in the back of your exhaust manifold somewhere?

Not that I can see. I’ll check it out and see if I can find any leaks, but I don’t hear any.

Now, it’s worth mentioning that for some reason, someone welded an additional O2 sensor bung on the top of my downpipe. No idea why it’s there, all I could think is that it was a wide band sensor for an AFR gauge, but I’m not totally sure.

bmdubya1198 said:

Not that I can see. I’ll check it out and see if I can find any leaks, but I don’t hear any.

Now, it’s worth mentioning that for some reason, someone welded an additional O2 sensor bung on the top of my downpipe. No idea why it’s there, all I could think is that it was a wide band sensor for an AFR gauge, but I’m not totally sure.

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I assume you know you can do a signal wire o2 voltage test at the connection under the hood ? I would try it there also, since the readings are not in the correct range.

Otto Mattik said:

I assume you know you can do a signal wire o2 voltage test at the connection under the hood ? I would try it there also, since the readings are not in the correct range.

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Yes, that's how I tested it before.

Tested the O2 voltage just now, it looks good at operating temp. It fluctuates between 0.2 and 0.8 as it should. False alarm on that problem!

Driving it today, it felt better than before. I think the sluggishness may be an issue of cam timing. As far as the low, twitching vacuum gauge, I have no idea what is causing that. It also does it in boost when it’s at full boost (10-12 PSI).

Have you tried a known good MAF?

I’ve tried 3, and one was definitely bad. I’ll have to borrow my cousin’s MAF just to test it.

bmdubya, check out the last few posts in VolvOrr's thread. See if any of it applies to your situation. I saw in an earlier post that you're using an iPD cam. You might need at least an adjustable gear, or in a worst case a different cam.