90 240 running rich
 

My 90 240 is running extremely rich. Gives a code of 1-2-3 at all three test levels. This signals temp sensor. Earlier, it signaled Air Mass Regulator, which I replaced. I've now replaced the temp sensor and the temp gauge works fine.
If I reset the codes, it runs about 2 miles before the check engine light comes back on. Lots of black smoke coming out of exhaust if I gun the engine at idle.

I've checked hoses, vacuum lines. Haven't checked fuel pressure.
Ideas?

there's two separate temp sensors, one is just for the dashboard gauge (and has a single wire), the other has two connectors, one each for the ECU and ICU.

best way to test them is with a ohm meter, at the plugs that goes onto the ECU and ICU.

see https://volvoforums.com/forum/volvo-...88/#post394811 so I don't have to write it all down again :)

ohm meter is worthless.

GMM signal wire.

huh? the ECT/CTS sensors are temperature sensitive resistors. low temperature == high resistance, high temperature == low resistance. an ohm meter is for measuring resistance. by testing the resistance of the ECT/CTS at the connector to the ECU, you are also verifying that the wiring is OK. ideally you test it when the engine is hot, then wait for it to cool down, and test it again.

frankly, I don't even know what a GMM is, and Ive been doing electronics since the 1970s.

A bad engine coolant sensor will cause your car to run rich. As Pierce said, it's easily tested with an ohm meter. I like to bench test it so I can put it in hot water (heated on the stove) and measure the resistance.

The 700/900 FAQ over on Brickboard has a nice writeup. The engine is the same on those cars so it applies to yours as well. Here is a link:

https://www.brickboard.com/FAQ/700-9...ingECTFailures

Pierce, thanks one more time. I don't know why I don't always just ask you first. But without blundering along, I wouldn't learn as much. I had a hunch I was looking in the wrong place.

The more I fix it, the worse it gets
 

Re: 90 240 running rich, all tests indicated the engine coolant sensor, so I replaced it and its pigtail. Had to pull the intake manifold to get there. Anyway, all went together ok, but now I have no spark at the spark plugs. Dash lights and starter work, so the current is going that far. I tested the ECU at the number 6 contact and there is no voltage there. Other than removing the distributor cap while installing the ECS and disconnecting the ground, I didn't fiddle with any of the ignition stuff. Seems an open circuit exists between ignition switch and the ECU, but I can't tell from wiring diagrams how to check it. I might add that the wiring diagram in my Bentley manual for the 1990 doesn't match my circuit all that well. The 1989 seems closer.

the bentley wiring diagrams are borderline unreadable. the best ones are in the volvo 'green books', year by year.

Thanks
 

Glad to hear you say that about the Bentley diagrams. I was beginning to think I was a complete idiot. Where can I get a 90 Green Book?

you used to be able to order the greenbooks from Volvo (for like $59 each, OUCH!), but they are all out of print now AFAIK. The VCOA (Volvo Car Owners Association or something) sells a DVD full of all of them for a given car family, but the scan quality on these disks is variable and in fact, the 1990 240 wiring diagrams page for LH2.4 injection is almost unreadable (luckily, its almost the same as other years, so I hop around to find a usable one).

these VCOA DVD's also have greenbooks on mechanical systems, fuel injection theory, and so forth.

green books
 

Thanks. I'll check it out.

After replacing the coolant temperature sensor, which required moving the intake manifold, etc., my 90 240 won't start. No spark to distributor. Shows 12 volts at both coil posts with ignition on, but no spark from coil. I replace coil. Didn't help. The only thing I moved on the main ignition system was removing the distributor cap to make a little more working room. It can only go back on one way.

I've checked various circuit components best I can, following the Haynes Volvo manual, which I find written more clearly for the wiring, etc. than the Bentley. Am truly stymied on this one.

i wonder if you didn't disturb the crank position sensor wiring? this CPS is plugged into the top of the transmission bell housing between the head and teh firewall. its the source of all timing information on LH2.4 cars (1989+). no CPS pulses means no fuel injection OR spark.

Thanks again
 

That's one I hadn't checked. Hope I can get to it.

Thanks

Score another one for Pierce
 

Pierce, you were right about the rpm sender problem. I didn't bump it while installing the coolant sensor, but I did manage to squash the sender wire under the intake manifold when re-installing it. 'Twas shorted out. Running again and the coolant sensor solved the richness problem. Thanks much.