[visionhawk]

Hi folks,
I have a rather strange problem that has most people here Down Under stumped...thought I'd try you colder climate types for some clarity of thinking !! (Not so easy to think when the temp here is 35C+ )

OK, the problem.
Car has had a sometimes buzzing main fuel pump, which frankly I had put down to the heat. Also a new pre-pump. But drove well.

Starvation forced me to go shopping, and when I returned the car started perfectly, idled perfectly, but when I put pressure on the throttle it surged forward then slowed, surged, slowed....you get the picture. Even downhill I couldn't get more than 10 kph. Managed to limp to my mechanic despite the fuming drivers around me, and he has checked the following:

* Main fuel pump (as car still idled the pump isn't faulty?)
* Air Mass Meter
* Air cleaner OK
* Throttle sensor
* Checked for a blocked exhaust (my 'cat' has died, shame it only had 1 life)
* Checked fuel filter (perfectly clean, I use the good stuff)
* Checked tank level ) (3/4 full) (Not entirely stupid)
* No diagnostic error codes
* And he is leaning toward the ECU but not convinced about it...
(By the way, this mechanic has had a fair bit of 7/9 series experience)

Sooo, has anybody had this behaviour before? Or any pointers as to what it might be? I've been without my Sven for over a week and have too little hair left to lose anymore!

Your thoughts would be gratefully appreciated.
Regards,
Michael

 

[BHart]

You'll have to try and narrow the problem down to a specific area. Is the stumbling there constantly or intermittant? If it's temporary, can you easily re-create the condition?

Did your mechanic attach a fuel pressure guage while the car exhibited the problem? Buzzing could be normal in heat or could be cavitation from a blockage. There's also a vacuum controlled fuel pressure regulator for the fuel injection. This would also be test-able with a fuel pressure guage.

If your shop has Volvo experience, is there any chance he's got a spare computer or an old car you can 'borrow' one from? It could be 'limp mode' if there's a problem there. Limp Mode default will cause it to run very rich.

btw, when it's -35c all you can think about is how damn cold it is....

 

[visionhawk]

740GL Kangarooing

Many thanks for your reply.
The problem is constant. As for the fuel pressure gauge, I'm not sure if he has done that test.
One thing I just remembered is that he said the injectors are not powering up - whatever that means!!

 

[visionhawk]

Culprit found !!!

As Clouseau would say... the problem, she is solv-ed.

After 6 weeks of diagnostics of all types....it is the fuel computer. I sent it away to a specialist, who said it was faulty. And when put back in.... no more kangaroo!!

I hope this happy result helps someone else who is wondering what the heck is going on )

Thanks to everyone, and good luck with your Swedes.....

 

[Paul]

Hi,
I have 90 740GLE and had the same problem. The ECM was the problem.

I have a good one for you. The engine would start some of the time. The only way it would start was to add a little starting fluid. Cpu was good,fuel pressure good,injectores good,fuel pump relay good,grounds good,pressure regulator good.Well to make a long story short it turned out to be the radio supressor located under the hood. Volvos seem to be a little complicated to understand at times.

 

[visionhawk]

Volvo foibles.....

Many thanks for your comments, Paul.

During all my internet research, I discovered that the solder that auto manufacturers use is different to the type used by electronics companies. After 10 years, it begins to crystallise, meaning the solder "shrinks" and allows cracks in the tracks on the circuit boards, causing intermittent weird failures. What's needed is to re-flow the solder on all circuit boards (instrument cluster too), although it's not a job for the uninitiated !!!
For those of us who just couldn't be bothered, we'll keep buying new parts )
Incidentaly, I have 2 of the same relays at the expansion tank....is the radio suppression one on the left or right?

Keep on rolling.......