9 replies to this topic

[tmurph03]

So, over the past month I have been dealing with a persistent problem where my 1994 volvo 850, which otherwise drives beautifully, stalls and then won't start again for an extended period (a few minutes to a few days). The car drives fine when it works: shifts smoothly, engine sounds like its firing fine, no real issues with its functioning when its functioning. I had a few mechanics look at it and the fuel pump pressure was fine, the cam and oxygen sensors were cleaned, the relays were changed and a broken ground wire was replaced. After all this, it still stalls. I eventually discovered that the ecu was fried and i changed it. The problem persisted after a period of great driving. I found that then the transmission control computer fried and i changed that too. It drove fine for a weekend and then the car stalled again. I know that there is one other computer module on this vehicle located next to the ecu 6.2 and the transmission control 6.3 that controls the fuel injection with the number 5.2 on it. I don't know how find this for sale. The other two seem to be common enough online to purchase, but i cannot find the 5.2. Does anyone know how to find this part? Does anyone know what it is officially called? Any thoughts on what is going on with my car, if not the fuel injection computer thing? Thanks for any help or advice you can offer.

[prasamin]

if your ecu's/computers are frying, then you have an underlying issue you need to resolve.
you need to go through your wiring harness and make sure nothing is shorting, and that everything looks okay....because the issues you're having are not common at all, nor are they supposed to happen.

have you checked your MAF sensor, throttle position sensor, cam position sensor, etc?

[tmurph03]

A mechanic recently cleaned the cam and oxygen sensors when this problem first began happening. Was going to check the maf sensor tomorrow and will take a look at these other sensors, too. Where might the throttle position sensor be?

One thing of note, if it helps with imagining the problem, the problem originally was it stalling out mid-drive, as if someone cut the engine/power. After changing out two of the ecu's, it seems to stutter to a stall. As in the rpm's drop and the engine appears to struggle to keep going. At the moment it won't start at all. Not sure if that leads anyone to believe it is one part or sensor or an other.

And thanks.

Also, after this final stall, i checked all of the ecu's and they appear to be in fine condition. No oxidation or indication of having been fried around this last stall.

[FCP Groton]

You must have a major short in the harness to have it blow the ECU. I would go over the wiring with a fine tooth comb.

[tmurph03]

Could it be possible that the ecu's were already dead/dying? The car is at 190k.

[tmurph03]

Cleaned the MAF and it now starts. Would it be wise to replace this? Or can I assume that it was only corroded?

[FAST850R]

I don't know whether the MAF causes stalling issue...I had stalling issue while I was driving, but I had a CEL. I just don't want you to change unnecessary parts unless you are sure of it.
I have never heard ECU dying because the mileage hits 190k. If ECU had problems, something is wrong, like other members say. I think you can focus on ECU wiring harness or related parts first since you had the ECU problems.
Because Mechanics said it's ok, it doesn't mean it's ok. I had a CEL problem for more than 1 year and took my car to multiple Volvo specialist shops, but nobody could find what was wrong. I asked to check specific items, and mechanics said they are all fine. Later on, I fixed the problem myself, and it was the item that I asked about.

Cheers.

[tmurph03]

Hmmm...looks like this one will have to go to the mechanic. I'm not familiar enough with the electrical harness to do that kind of a job. As for the ECU's, I've just read that they go on these models and the original mechanic, who serviced this car for the first 17 years of its life, scratched "check at 200k" on the ecu casing. Figured he knew something was likely to go then.

I still think the MAF is problematic. It was covered in blue/white oxidation along with all the ports to the MAF and some other sensors/valves. cleaning all that off, but I think I see your point about it being primarily an electrical issue. The sound of it stalling though, is as if it is being chocked of fuel, either gas or oxygen.

Off to call the mechanic.
Thanks for all the help everyone.

[zomaster]

i've had a similar problem-- thought i fixed it but has returned, and that's why i came across this thread just now trying to resolve my problem--and one part of it was that my ignition coil died. eventually the car would no longer start after repeated tries and i discovered the coil just wasn't producing spark. i replaced it and car was good for a while. months later i replaced the cam and rpm sensor when i was getting intermittent stalls and skips on hard acceleration (just as i did before the coil issue), and again i was good, but now car is acting up again in the same way! who knows what needs to be replaced next. car has 200k on it so it can probably be anything. i will check the iac and fuel pump this afternoon but i think the walbro pump only has about 75k on it and in my 3 past experiences when a fuel pump goes out it doesn't ever work again and this is not the case for me.
i wish myself and others out there good luck

[zomaster]

since i just posted the above i might as well follow through with my results. looked again under the hood and saw the intake tube on the turbo wasn't quite on. didn't notice that when i looked a couple days ago, guess it finally came loose enough where i saw it this time. always check the easy and obvious first, and then a second time!