New problem. Engine stumbles

[mhuk]

Volvo 940 turbo b230fk running chipped ECU / S70R injectors / ect ect


Out driving with a friend to the south coast to pickup my daughter.

After around 30 miles I start getting a problem.

@ little throttle and while cruising around a speed of 40mph. The engine will loose power output.

The rev counter stays at whatever rpm it's at. The turbo gauge stays in vacuum and does not move. The speed of the car slows down as if I had depressed the throttle.

I have to push the throttle down and the power returns with a thump as if I was depressing the clutch and letting it back out again without being gentle. As I press the throttle down I see the vacuum decrease and I start to edge towards producing turbo boost.

The O2 light comes on.

2 minutes later this happens again and all the way to the coast and back to London. 140 miles round trip.

The problem only happens while cruising and when in vacuum. Pushing down on the throttle clears the problem but it does return later.

Things I have noticed. When the car is at idle the exhaust pressure on my hand feels normal. My friend revs the engine and out comes more exhaust but then it stops for maybe 1 sec. Nothing exits and then it blows loads out.

The engine IDLES @ 1500 all the time now! It was OK after the problem but day later it's worse at 1500.

I already asked on a FB page for advice. Suggestions made.

EGR valve (don't have)
CBV leak. This is the valve on the turbo cold side housing?
MAS? Think they meant MAF

This is what I have done.... I took the rear exhaust box off. Hoping it was blocked. No change.

My down pipe is 3" and has a exhaust cut out flange and it's not currently in use. This is POST down pipe and PRE car. I took the blanking cover off and IMO the exhaust should take the path of least resistance. It's loud as hell now so if It's blocked it can only be the down pipe? It's not looking like it's damaged on the outside but I would need to come off and it's not a hard job I think. Think V bands!

This morning I have connected my smoke machine to the inlet manifold and I can find no vacuum leaks.

What confuses me is.... When running the turbo it's fine. Plenty of power.

Thinking about fuel pressure injectors but that would show under heavy load.

Bad O2 sensor?

Cheers guys!

[Laird Scooby]

Remove and refit the fuel pump relay and also all the fuses. It could be a fuel pump problem causing temporary fuel starvation. Also check the RSR (Radio Suppression Relay), this could be causing a temporary loss of power to the injectors, the Lambda sensor isn't prime suspect on this as the engine will still run without it - not advisable but it will.

You could have a loose baffle in one of the boxes and/or the cat causing a temporary blockage or you may have a bad earth connection somewhere on the engine.

[mhuk]

Thank you. It be that the revs stay because it's still spinning over in gear and then kicks back in. I will take a look and advise.

[mhuk]

Is this the rsr repay? It looks ok on the inside.

I replaced the fuel pump relay. It looks ok too.

Cheers

[Laird Scooby]

Originally Posted by mhuk

Is this the rsr repay? It looks ok on the inside.

I replaced the fuel pump relay. It looks ok too.

Cheers

It looks like it, there are often two and they're the same part number, the other is for the electric cooling fan if yours has one (usually cars with A/C have an electric fan) but if yours only has the one relay then almost certainly.

It might also be dirt on the connectors in the plug that connects to the relay causing the problem.

Did you pull and refit all the fuses too?

[aardvarkash10]

intake blockage is my guess from your described symptoms. Relatively easy to check the intake side with a vacuum gauge - I'd check for vacuum (there should be none or near zero) just before the throttle under the running conditions you describe. If it DOES have vacuum there something is wrong.

[mhuk]

Originally Posted by Laird Scooby

It looks like it, there are often two and they're the same part number, the other is for the electric cooling fan if yours has one (usually cars with A/C have an electric fan) but if yours only has the one relay then almost certainly.

It might also be dirt on the connectors in the plug that connects to the relay causing the problem.

Did you pull and refit all the fuses too?

Hi,

2? I only see one and I have electric fan (was AC car) I also have the low impedance mod for the injector done by the PO of the car.

Yes I took all the fuses out and put them back. I have started the car and the O2 light stayed off while I moved it from the road to the side alley which meant it was running for maybe 4-5mins. I can't check if the exhaust now feels OK as it's just me. I might need to employee my parents for this.

I'll give those connectors a good clean too tomorrow if it ever stops raining. I ideally need the car running better for the weekend as I'm seeing my daughter again.

[mhuk]

Originally Posted by aardvarkash10

intake blockage is my guess from your described symptoms. Relatively easy to check the intake side with a vacuum gauge - I'd check for vacuum (there should be none or near zero) just before the throttle under the running conditions you describe. If it DOES have vacuum there something is wrong.

I can't think what blockage it would have intake side. When I was thinking blocked exhaust I thought about the baffles blowing out.

[aardvarkash10]

Originally Posted by mhuk

I can't think what blockage it would have intake side. When I was thinking blocked exhaust I thought about the baffles blowing out.

Blocked exhaust would result in decreased intake manifold vacuum - the guage would show a steady decrease in vacuum until the blockage cleared, then a rapid return to normal vacuum. From your description, blocked exhaust is not a first choice candidate.

[Laird Scooby]

Originally Posted by mhuk

Hi,

2? I only see one and I have electric fan (was AC car) I also have the low impedance mod for the injector done by the PO of the car.

Yes I took all the fuses out and put them back. I have started the car and the O2 light stayed off while I moved it from the road to the side alley which meant it was running for maybe 4-5mins. I can't check if the exhaust now feels OK as it's just me. I might need to employee my parents for this.

I'll give those connectors a good clean too tomorrow if it ever stops raining. I ideally need the car running better for the weekend as I'm seeing my daughter again.

It's possible the relay you've found was the cooling fan relay in that case - where was it?

Also tell me more about this "low impedance mod" for the injectors?

Can you also give the Bosch part numbers of the injectors you're currently running?

I'm hoping that what you've done so far (which will have cleaned the raly connectors, fuses and holders) may have sorted the problem but i didn't realise there were modifications to the original wiring. This may be the source of the problem and possibly explain the abscence of the RSR relay.