So, I put a new O2 sensor, the thing wasn't working well anyway, hadn't been changed in probably 135,000 miles. But it's still running very rich, fouling the oil, at least enough that I can smell it. It gets about 10-12 miles to gallon. I read that a wrong idle mixture will do that. I'm not sure how to change it on the 740 GLE though. The throttle's different than the one my Haynes book shows.

Also, I guess if the intake manifold was leaking, the computer would read a falsely lean mixutre and richen it, right? How do you tell? Didn't somebody here say spray it with carb cleaner while running?

here's a list of the new stuff on it:

fuel pressure regulator
throttle position sensor
coolant temp sensor
oxygen sensor
new plugs
professionally cleaned injectors (working fine)


Thanks, and this site's really been an informative place

 

Yes you can spray carb cleaner and if the idle changes there is a vaccum leak there.
Also could be a bad mass flow sensor.

 

Thanks. I guess the only way I knew to check the AMM was to unplug it and start the car. There wasn't any change whatsoever. Sprayed carb cleaner on the intake, and no change in idle. The mechanic who worked on it before said the rich mixture "puzzled" him. I'm puzzled too, it runs pretty smooth when I get it up to 60-65 mph, but at idle, it wants to die out, puts out dark smoke, and idle rpm's too low. I had a mercedes with a vacuum leak that did that. Maybe I should get another mechanic.

 

Something is very puzzling about it.
You might want to find someone that knows those older Volvo's very good.
They should be able to figure it out pretty quick.
The engine control module might also be bad.

 

If it's running rich, you can tell by unplugging a vacum hose that's connected to the manifold.. the addition of more air will make the RPM's go up.. If it's rich, then the vaccum leak is not your problem. If there was no change in idle when you disconnected the AMM, then that's your problem.. I'm diagnosing a 94 940 turbo wagon and did the same tests.. disconnecting the AMM made the car stall right out. If you got no change in RPM at all when you disconnected the amm, thent hat's your problem part.

 

When you disconnect the AMM the car should stay running it goes into limp home mode.

 

I too have a 90 740GLE that had a bad AMM. For some reason, these cars don't (or at least mine didn't) go into limp mode when the AMM signal is faulty. My problem was intermittent stalling because of a broken wire inside the meter that would loose contact at random times. I was able to diagnose the problem by using a handy feature our cars have called a diagnostic socket. Since these cars were manufactured before the advent of the OBDII diagnostic system, you're mechanic may not even be aware that there is a way to test for trouble codes on this car. The socket is located on the drivers side near the firewall adjacent to the brake master cylinder. It has a black snap on cover and is only about 2 inches by 4 inches (easy to miss if you aren't looking for it). The nicest part about it is those wonderful Swedes designed it as a stand alone unit-meaning you don't need to buy any sort of expensive code reader to access the info from it. There is a probe on a tether which fits into each of the six sockets on the unit. The Chilton's manual shows the method for using the unit plus all of the trouble codes it produces. Hope this helps. Best of luck.

 

Thank you. I'd wondered what that box was, but didn't think about it much, and I have no idea whether the mechanic used it. I'll have order a Chilton's manual, I've got a Haynes, but it isn't worth a crap with these problems and doesn't mention the diagnostic socket at all.

I went out and bought a new AMM anyways, and it runs better, idles better, though the rich mixture persists. Hopefully the ECU isn't bad.

Other than that, overdrive comes and goes, figured it's the wiring or the relay, since it gets worse once it heats up, and sometimes motion engages it, or turns that arrow off. Or maybe the overdrive solenoid, but they're not tooo expensive. Nobody here in town (panama city) wants to do any rewiring on a Volvo. Thanks man.

 

Went to www.swedishbricks.net where it tells how to use the diagnostic socket, and gives all the error codes. Here's what I got just a few minutes ago:

1-2-3 Signal missing to/from coolant temp sensor

2-3-2 Fuel trim too lean or rich at idle

3-1-2 Signal missing for knock related fuel enrichment (I'm not sure what that means, the knock sensor?)

Coolant temp sensor is brand, but wiring may be bad. Fuel pressure regulator also brand new, but could it be keeping line pressure too high?

 

I would check the wiring for the coolant temp sensor.
The fuel trim code usually means a vaccum leak.
The knock sensor code I wouldn't worry about it to last.The other codes migth have thrown that code.

 

I can't see any obvious defects with the wiring to the Coolant Temp Sensor, though it's reading no signal. I've never done wiring on a car before, so I'm sure how to approach it. Does anybody sell the stuff premade with the clips and all?

 

Is your sensor 1 or 2 terminals?
Check the harness buy where the engine harness meets the body side of the harness.

 

1 terminal. I've checked the harness, but nothing obvious. I called www.volovofhouston.com, and a new wiring harness for 90 740 GLE costs $669. Does that sound close to right?

 

Sounds pretty close.
But you might have another sensor as well the 1 prong should be for the guage.If you ground it out with the key on the guage should read hot.

 

The coolant temp sensor for the ECU is buried under the number three intake runner, just to the right and up a little bit from the flame trap, and has a two prong wire bale type connector that looks like the ones on the IAC and TPS. It's a little hateful to work on, and really take a mirror to see it well . It is easier to just go ahead and remove the intake manifold for testing and/or replacement.

 

just an update:

got around to checking all the vacuum lines, all seem good, and the thing's got a lot of vacuum, although there could be something.

I figure at this point, it's all about the Coolant Temp Sensor, no signal to/from it to ECU. No signal causes the ECU to assume it's 60 degrees, and puts a ton of fuel to it, right?

well, I gotta get off my *** and trace the wires. Thanks for all the help!

 

Make sure the wiring harness is in good shape and wires aren't touching.