Myserious power loss

[matth76 0]

Hi

 

Just had a rolling road session with Stealth. My car is now making 190bhp instead of its original 207bhp. Nothing at all has been altered on the engine since the last rr session. The only thing to have happened since my last rolling road session is that my car overheated back in May/June when the thermostat went. However my car's oil temp at the time only hit 118 and since then no water has been lost (meaning my head gasket is fine) and the car still drives very smoothly. I wasn't aware anything was actually wrong until I had the rolling road session yesterday.

 

Vince at Stealth is puzzled as to what could cause it. The power curve it now has at 190bhp is very smooth, exactly like my previous rr session power curve but now with 15bhp less.

 

Because the power curve is smooth he says all cylinders should be ok... if one wasn't ok the power curve would be irregular and choppy. He thinks it could be partially blocked injectors causing the power drop. Or the alternative is that there could have been some very very slight friction damage when my car overheated... although the oil temp only hit 118 so it seems unlikely, even more unlikely because Vince said the car drives very smoothly.

 

When my car was on the rr yesterday there was a high activity of knock sensor activity (keeping pinking in check) which was puzzling. However the knock sensors did their job and there wasn't any pinking at all. No oil was being burnt either at all. Vince tried chaning the custom remap (stealth's own rechip) on my ecu a couple of times to adjust the settings but my power refused to budge from 190bhp. Very strange. Anyway I am currently trying out some of Stealth's recommended injector cleaner to see if that makes me get my power back although I'm not hopeful about this. I suspect there must be some thing else not quite right. Stealth were extremely helpful, they had my car for 4 hours in total (gave it a full service followed by rr session) and for 2 hours were checking out what the power loss problem was basically for free...great guys.

 

My current mods are Stealth's rechip, full s/s exhaust and high flow cat, s/s 6 branch (with a very very slight blow - but was assured this would not cause any power loss), BMC induction kit and 268 cams.

 

Any ideas as to what could cause my power loss? Anyone else had this happen to them?

 

Thanks for any help or comments.

[VR6 0]

Fair enough asking the question, but if Vince doesn't really know then I doubt you're going to get the definitive answer you're looking for .....

[CorradoVR6-Turbo 0]

Were both the RR at stealth?

[dr_mat 0]

I blame the slightly blowing 6-branch ..

Leakage at that point could cause problems with fuelling, which can very well lead to pinking (and ignition retard) if it results in underfuelling.

 

OR, the obvious bunnies are fuel pump, fuel filter, fuel pressure regulator ... yada yada ...

 

To be fair to Vince I'm sure he would have thought of those too, but I doubt they would have had time to test everything.

[matth76 0]

I blame the slightly blowing 6-branch ..

Leakage at that point could cause problems with fuelling, which can very well lead to pinking (and ignition retard) if it results in underfuelling.

 

OR, the obvious bunnies are fuel pump, fuel filter, fuel pressure regulator ... yada yada ...

 

To be fair to Vince I'm sure he would have thought of those too, but I doubt they would have had time to test everything.

 

 

Yes both the full service and rr was at Stealth. Vince did a great job...he did suggest the 6 branch and the all the possible causes you mentioned dr_mat...and exactly as you suggest, basically didnt have time to test them, otherwise would have done. Only had Sat morning unfortunately. I wasn't sure if anyone had had this same thing happen to them and could possibly narrow down the component most likely to cause this. He did say he wanted to try putting back on the original 6 branch and see how it was after this... I may do this in the near future as I was thinking of doing this anyway as the noise from the blow was getting a bit annoying.

 

Cheers for the replies.

[Shaggy 0]

i have a pinking problem with my car at higher revs.... i am starting to think that maybe its due to a leak somewhere... either through inlet & manifold or the injector seals... if a car has been custom mapped any slight problem with the car will show up 10 times worse than it would than with a standard car as its that much more refined when the car is spot on...

 

I think its just gonna be a case of checking everything and changing / fxing what you know could be the problem and take it from there... your main one being that blowing manifold.

 

I have checked pretty much everything on my car including the fuel pump and all is ok yet the car still pinks at higher revs... causing the knock sensor to kick in and steal 5 psi of boost and blow it out of the ISV...

[Roger Blassberg 0]

Could it be that the atmospheric conditions varied between one session and the other? Hot, dry air will lead to a power loss compared to cold damp air. Clutching at straws really..... I'm sure that Stealth would make the necessary adjustments to the readings.

 

Best wishes

 

RB

[matth76 0]

Could I have a vacuum leak somewhere? Would this cause a 15-17bhp drop in power?

 

Spoke to Stealth and they say they don't think the slight blow would cause such a drop as 15bhp...maybe 2 or 3 bhp at most. I know what you mean about a custom map... however Vince tried several different maps however no amount of changing would make any difference to the power. The power was still really smooth... just 15bhp less ... real mystery. Vince also said my fuel was not running lean at all... adding to the mystery!

[dr_mat 0]

I gained 10 lbft across the range with a replacement MAF. Might be worth a punt .. ?

[matth76 0]

Thanks Mat. Vince said the Maf was probably ok and not causing this. Although without actually changing it and testing it he wasn't sure what could be causing this. Does sound like a big increase you gained after changing your maf. Was your car still running smoothly before you replaced the maf?

 

How much are reconditioned mafs and where could I get one?

[dr_mat 0]

Smoothly enough. It just wasn't very responsive though.

One other thing. I have heard that it's possible for the timing collar on the rear camshaft to come loose - if this were to slip back the engine would have the ignition retarded all the time, but it wouldn't show up as retard in the ECU.

Not sure how feasible this is, but run it by Vince.

 

Recon MAFs aren't cheap. But buy a 2nd hand one on ebay, if the car drives differently, then it's likely that something was up with the other one.

[Kevin Bacon 5]

It think you mean a cracked/broken plastic cam sensor trigger. There is no 'collar' as such. The sprocket just locates into the cam with a woodruff type slot, but no seperate key to bend. If that moves you're doing well!

 

My money is on the MAF.

 

Or it could be the CAT getting blocked up. My own Milltek "freeflow" cat is certainly less than freeflow at the moment.

 

Leaking manifold would cause the lambda to over richen the mix, to the tune of 15hp, it would need to be a feckin great leak.

[dr_mat 0]

Yeah, that's the bunny. Just wasn't sure about it, thought I'd mention it.