"Hunting" in Volvo 740 GLT

[Peterquest]

Thank you for your suggestions

I've check the timing and this seems correct (ignition and valve), although I had to re-mark the crank pulley as this had slipped. After reading the codes it came up with no idle air control valve signal, I've checked the wiring and continuity seems ok so replaced idle air control valve and still no joy

anymore ideas?

[Laird Scooby]

Originally Posted by Peterquest

although I had to re-mark the crank pulley as this had slipped.

Can you explain please?

[Peterquest]

Sorry for the delay in replying. I understand from the mechanic that the pulley can slip and this one had. However, the timings have been checked and are fine.

I have now discussed the issue with a local garage who said we have done all that they would do. They suggest either taking it to the main dealer or identifying a local Volvo expert who is prepared to drive over and have a look.
I guess the main dealer will want it trailering in to the workshop. So does anyone know an experienced local person who might have the answer? We live in St. Ives, Cambridgeshire.
Thanks for your interest!

[Laird Scooby]

Originally Posted by Peterquest

Sorry for the delay in replying. I understand from the mechanic that the pulley can slip and this one had. However, the timings have been checked and are fine.

I have now discussed the issue with a local garage who said we have done all that they would do. They suggest either taking it to the main dealer or identifying a local Volvo expert who is prepared to drive over and have a look.
I guess the main dealer will want it trailering in to the workshop. So does anyone know an experienced local person who might have the answer? We live in St. Ives, Cambridgeshire.
Thanks for your interest!

You could try Kings of Witcham at Witcham Toll near Ely. Whether they would come to you or not is another matter but they are independent Volvo specialists. Are you a member of any breakdown organisation? You could possibly drive 1/2 a mile from home and "conveniently break down" and get them to tow it to wherever. Depending on how your breakdown policy is worded though they may only tow you to the nearest garage or back home so you'd need to be careful.

Other than Kings i don't really know of any Volvo specialists but you might be better finding a Bosch petrol injection specialist and may even find one closer to you.

[Peterquest]

Many thanks, Dave.

[mocambique-amazone]

I understand from the mechanic that the pulley can slip and this one had

yes they are prone to do this.
Renew asap!!!!!
I've seen hard damage under the hood by crank pullyes which start to fly, no joy.

Because I'm a German I have no clue about the sentence of "hunting" of a engine.
You won't mean killing something with a weapon ;-)

your car is with a B204F or with a B200F?

with a catalyst or without?

good luck, Kay

[Laird Scooby]

Originally Posted by mocambique-amazone

Because I'm a German I have no clue about the sentence of "hunting" of a engine.
You won't mean killing something with a weapon ;-)

Kay - i'll try to translate into an English phrase that will hopefully make sense to you.

"Hunting" is used to describe an engine that is idling erratically but rhythmically, up and down around the set idle speed usually although the lower end of the cycle can often be idle speed with the upper end at say 1500 rpm (higher in bad cases) and the process is continuous.

The word "hunting" is used as an analogy because the engine is seen as "hunting for its correct idle speed".

Does that make more sense for you?

[mocambique-amazone]

Thanks Dave.

The car revs up to 1500-1800rpm and interrups?
A really stupid fault will have a result like this:
Broken TPS

Disconnect the TPS, if the fault is gone (you will have no good idle, the engine will stall if you go of accelerator) it's the TPS
If the fault is still there check the wiring to the ECU
Maybe a short cut.
If I would know which engine I could tell you the pin-numbers

Good luck, Kay

[Laird Scooby]

Originally Posted by mocambique-amazone

Thanks Dave.

The car revs up to 1500-1800rpm and interrups?
A really stupid fault will have a result like this:
Broken TPS

Disconnect the TPS, if the fault is gone (you will have no good idle, the engine will stall if you go of accelerator) it's the TPS
If the fault is still there check the wiring to the ECU
Maybe a short cut.
If I would know which engine I could tell you the pin-numbers

Good luck, Kay

I'm not sure what the range is that it's hunting over Kay. From what i've understood it will rev but is hunting at idle.

Usually i've found it's down to an excessively weak mixture so the engine is about to die, the ECU compensates by richening the mixture so it over-revs for idle conditions so the ECU shuts the fuel ff again until the engine speed drops and then it drops too far. As such, the usual cause of the weak mixture is an air leak.

[Peterquest]

Before telling you what has been done I re-emphasise that this Volvo is hunting on acceleration, not on idle. This occurs over 1200 rpm but makes the car unusable. We took the car to Kings (Volvo specialists) as suggested and they have tried hard over many weeks to get it going but without success. They have tested extensively (a lot of this is now for the second time) and have replaced rotor arm, ignition lead set, ignition cable and plugs, ignition module, and crankshaft position sensor. Kings have consulted Volvo technical without any successful ideas. They have also spoken to others but no-one has experience of hunting on acceleration (all know about hunting on idle); if you have, please let us know. YOu can see other work that we have done earlier in this thread.

Kings didn't have access to an oscilloscope so we have purchased an old one off ebay to test the injectors. I have put a letter in the Club magazine asking if anyone has experienced this type of hunting - this comes out in October.

So - let us know if you have any thoughts!!