1990 245 Auto running rich, 10mpg

I have tried to avoid posting this question here for the last couple years because I really hoped I could solve the problem myself, seeing as I have been a professional Volvo mechanic for nearly 2 decades. But, I am fully stumped. The engine is mostly stock. It has an A cam installed, 2.5" exhaust system and that's about it. It runs extremely rich, so much that it makes my eyes burn to drive it more than 15 minutes or so. If I reset the ecu, the check engine light will usually come back on within 30-40 minutes of driving. It gives a code for coolant temp sensor, and engine running lean/rich. I have replaced temp sensor half a dozen times. I have swapped several known good AMM's, several known good ECU's and ICU's. I have eliminated the Temp sensor wiring, by completely bypassing the harness and running wires directly from the sensor to the ECU and ICU. I've replaced the O2 sensor. I have checked for vac leaks. I've checked the fpr. I've checked the resistance of the temp sensor at the computer, and it is within range. I am at a total loss.

The car runs pretty well, but I can tell that there is some power on the table because of how rich it's running. What am I missing here????

have you checked your fuel pressure? you may have a restriction in the return line back to the tank causing excessive fuel pressure and in turn creating an overly rich condition.

Have you tried different injectors?

Does it run ok in open loop? What does the O2 sensor voltage look like once everything is warmed up? Pegged at 0.9V?

Just a couple ideas:

- bad ECU grounds at the intake manifold or in the cabin.
-Poor oxygen sensor wiring
-loose terminal tension at the ECM or O2 sensor connector
-leaking injectors
-poor grounds at the block

I avoid/overlook it too, but I would probably start doing loaded voltage drop testing on suspect circuits and get out the correct terminal test probes and do drag tests on all your female terminals at the ECM/ICU, O2, and ECT connectors.


-Edit- Good call on double checking the basics of fuel pressure. I have 1992+ fuel rails on my cars and the IPD 90 degree fuel pressure guage adaptor.

FYI - You can find the LH2.4 fault tracing greenbook under TP31361 at ozvolvo.org/archive/

[Just to sure, the LH2.2 temp sensor looks like the LH2.4 temp sensor but isn't interchangable -- LH2.2 has 1 sensor with 2 terminals and no block ground connection, while LH2.4 has 2 sensors with 1 terminal each and grounds to the block.]

^Good points...

There aren't any holes in the headpipe, perchance? Not uncommon to develop holes on the non-turbo headpipes. One thing you could try is a pre-'89 exhaust manifold, if the car is a non-California spec non-EGR car. Move the O2 sensor to the manifold. If it starts running normally, then, there's a leak somewhere between the manifold and the cat...

Good calls on checking for exhaust leaks. We have a special smoke machine to shove in the tail pipe for finding tricky exhaust leaks.

I know that the ECT code on this car can be a misleading one. The rich/lean code is generally a code that is accurate.

Something makes me think your O2 sensor is giving a skewed reading and then throwing the mixture way off. Thats why I would monitor, maybe even graph out the O2 sensor voltage and maybe something will be obvious.

Let's put a microsquirt in it this weekend

ZVOLV said:

Good calls on checking for exhaust leaks. We have a special smoke machine to shove in the tail pipe for finding tricky exhaust leaks.

I know that the ECT code on this car can be a misleading one. The rich/lean code is generally a code that is accurate.

Something makes me think your O2 sensor is giving a skewed reading and then throwing the mixture way off. Thats why I would monitor, maybe even graph out the O2 sensor voltage and maybe something will be obvious.

Click to expand...

Yep. The '92 245 I used to drive pretty much always showed a 2-1-2 or 2-3-2 code, due to a crack that had formed in the headpipe. Since WA didn't test emissions in my area, I just kept driving the car. Mileage did go from 28-29 mpg at 60-65 mph to 24-25 with the leak, so not the massively huge difference that Eric is noticing on his wagon, but still noticeable.


Another possibility might be the cold start injector. I wonder if it's leaking. Or, is somehow injecting fuel at all times, instead of when the car is stone cold. Might be worth unplugging and see if things improve. Alternatively, if only 556 and 561 ECUs have been used, try a 951 or 946 in its place, since those did delete the cold start injector circuit, apparently. They also do have the faster processor chips in them.


The other weird symptom I've seen with the LH 2.0/2.1/2.2 CTS, is a failed sensor, new in bag, from Bosch. Had an '84 245GL a while ago that ran ok, before I replaced the sensor with a new Bosch coolant temp sensor. Afterward, the computer ignored both the oxygen sensor and the air mass meter. Just ran like crud. Black smoke, raw fuel odors, the whole thing. It eventually started running ok again for a while, then, decided to run full lean. Wouldn't go up a hill when cold unless it was running full throttle in 1st gear. Unfortunately, due to that, the head gasket decided to leak. Not enough to cause the temperature gauge to read high, but it definitely had the stench of a bad HG. Replaced the head with a used head from a B23FT longblock. Reused that head's coolant temp sensor, which looked original. Car ran normally. No weird odors, normal acceleration when cold, etc.



Alas, what finally made me retire that car was a valve shim bucket that was somewhat loose, causing a very loud "takka-takka" sound while running. That's when the aforementioned '92 245 entered the picture.

Thank you all for the input. It has been a while since I have scoped everything out. And frankly, I just got so annoyed with the car that I stopped driving it. But now that I'm daily driving it again, I am motivated to give it a fresh look. I am pretty confident I don't have any exhaust leaks, but I will take a second look. But I will definitely take a good look at the O2 sensor again, as well as cold start (can't remember if my car even has one), and the grounds. I am wondering if the grounds might be the issue. I have tried every ECU ever made that should work on this car, and none of them fixed the problem. It could be one of the female pins in the ECU connector, I'll take another look at those as well.

I did check the fuel pressure, and it was spot on. I blew air through the return line, and all was clear, I could hear it bubbling in the tank. I have tried a few different sets of injectors as well, to no avail.

Harold, I'm down putting microsquirt in this thing if that's what it takes. I'm sure it would rip pretty good with a juicy tune on it. I tell you what, if I had a rear-ended chevy van in my driveway, I would yard the motor and trans out this weekend and stuff it in that wagon. That would solve all sorts of issues!!

Thanks again everyone, I'll get going on diagnostics and see what I can come up with and report back here as soon as I can.

I have an update!!!! I think I figured it out! So, I got home tonight, with full intentions of going through the green book to diagnose every possibility. So... I think I fixed the fuel problem with my wagon. I got home and prepared for an ultra deep dive into LH2.4. I checked all the grounds, good. I checked the ecu main plug, good. I checked the amm, good. Temp sensor, good. Knock sensor, good. Vacuum leaks, nope. Exhaust leaks, nope. O2 sensor, pegged high. Sweet, I thought. I replaced it with a new one (had a few on the shelf), but it still pegged high. Then I took a look at my stash of lh2.4 computers, and noticed that one of them, which was the same part number as the one in my car, said no cold start valve written in paint marker on it. I went over and looked, and sure enough, my car has a cold start valve and it's plugged in. I unplugged the valve, reset the computer and warmed up the o2 sensor a bit, and then it is reading normal, cycling like it should. And then I went back and took a big wiff of the exhaust, no more fuel smell!! I just got back from a 30 minute test drive, driving the hell out of it and I don't smell any fuel, and the fuel gauge didn't even budge! And, the cel didn't come on. Holy cow, I'm relieved.

Thank you guys for all your input. You all helped me figure out this long standing problem that was so simple, yet so hard to find. I appreciate you all!!!

Good fix.

Glad to hear you fixed it nice work.