RWD - '89 240 barely idling, gas in exhaust

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'89 240 barely idling, gas in exhaust 200

Hi there,

You might be on a good trail as the ECT can cause an overly rich engine response.
If it's unplugged or a bad wire this will cause a false signal or lack of one actually and will make the ECU think its in an Alaskan winter!
Only trouble is, I want to say they rarely fail but that's not never!

There are other things ..... You might have a bad AMM, a leaky cold start injector or still a bad FPR. Especially, if it's not returning the proper amount of fuel back to the gas tank.
Too high of an operating pressure on the fuel rail will provide too much fuel and the ECU cannot trim the pluse on-time length back enough.

A "no volt signal" from the O2 sensor will make the ECU think the engine is running lean but by default, the ECU should not go that rich. That's why you were still able to drive the car so long but not at its top edge (Lambda) in efficiency of fuel economy or emissions performance.

I don't blame you for letting it go!
I know they are overly priced so I use a universal one for $20!
I ignore the stupid ceramic heater inside.
It doesn't take but a few hot licks of exhaust to out strip the time it takes to warm up the sensor electrically.
The other ones, are a consumer rip off! I have seen them for as much as $250+!

If the AMM fails, you end up in a "limp mode." With the key or engine off, try unplugging the AMM. Run it and see if it will idle better but it won't drive off or around worth a darn!

It's sort of a way to check it out but replacing it with a known good one is about the only way to rule it out.
I would advise you to check for corrosion on the both pins or a receded terminal up into the plug side. This causes the AMM to give bad information to the ECU.

You can check the value of the ECT directly on the component. Its hard to get clips down inside the connector end while its under that manifold.
I have a junkyard connector I plug into mine with extended leads I can hook my meter onto.

You might want to search FAQ's for more information on how it is done from the ECU connector.

This will check out the wire coming from the engine and through the firewall and puts things in front of you. It also puts you on your knees so, you can beg for a fix, more comfortably! (:-)


I found this information above on the pin-out but I'm not familiar of how to interpret the side bar information.
Yours is a '89 so that half of the side note does not apply anyhow?

This other method, expressed in the side bar, must be done with the key on and I assume one must back probe that big thing!
That is what scares a novice like me out of monkeying around with it POWERED and ah-doing some poking from the back side blindly doesn't help!

I use that Bentley resistance reading with the engine off of course, because I can unplug it and peer in there.
I just know it says the pin 13 is the place it drops in.
Going to it with a meter and a "good" ground connection with the other lead, might give you a better overall / continuity resistance reading.

If Art Benstein chimes in, he can shine some of his wisdom on how he does all this!

I bet he has written a post somewhere! Use the FAQ's and ECU & ECT in the same line?

Good luck!


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New 1 '89 240 barely idling, gas in exhaust [200]
posted by  LoveMy240Wagon  on Thu Aug 18 17:53 CST 2016 >

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