Poor performance from early Vr6

[bruny 0]

:help: Any technical experts out there with any suggestions to poor performance from a 92 Vr6???

Rolling road only showing 120bhp at 5000rpm :( air/fuel ratio basically 14.7 up to 4500rpm then it drops to 13 @5000rpm. Didnt go any further through the rev range as too weak mixture might have done some damage :shrug:

First thought was Mass air flow meter, so did a swap with a reconditioned exchange unit and tried again, very little difference in output or AFR.

Tried running with MAF disconnected, we struggled getting it to run but AFR showed 15+ at 3000rpm, so guessing it is actually working :shrug:

Tested fuel pressure which seems to be spot on!

Tested trottle position sensor which was reading correctly!

No obvious air leaks on intake or exhaust side!

Nearly sure its a fuelling issue but what are we missing :confused4: any suggestions appreciated

[CorradoVR6-Turbo 0]

coilpack or dizy mate?

[bruny 0]

Distributer, think its a fuel problem though!

[CorradoVR6-Turbo 0]

have you checked for fault codes?,check your lambda sensor,the plugs tend to corrode away.

 

Has this just happend or did you always have this fault untill it was RR?

[bruny 0]

Have not checked fault codes yet but its booked in to JBS in Chesterfield on thursday unless I can sort it before hand.To be honest this problem has sort of crept up on me in so far as I dont drive it hard most of the time and have been concentrating on cosmetics initially, now thats basically sorted turning my attention to the motor department, it should have more grunt!!!

The motor will be rebuilt in the winter [chains/clutch/head/shells etc.] 104k on the clock, dont think it had an easy life before me!

It seems to be burning all the fuel so doubt that it would be a plug 'cos that would result in unburnt fuel going thru'??? [i am no expert though,] for some reason it isn't getting enough fuel injected in the first place! :confused4: :scratch:

[CorradoVR6-Turbo 0]

the ecu will limmit the ammount of fuel going to the injectors due to one of the sensors or more not working or giving the incorrect signal,(limp home mode)so unless the ecu has all its parameters working correctly it wont have the power it should. Hope you get it sorted bud.

[bruny 0]

Thanks for that will check it out! :) Will post up the result let you know whats up :scratch:

[dr_mat 0]

Fuel pump on it's way out? Fuel filter blocked? Did you check the fuel pressure while doing the run?

 

FWIW if there's sensors faulty, the ECU will typically run the engine rich and back off the ignition timing to protect it from pinking.

[bruny 0]

Fuel pressure is good,pump and filter ok I think! AFR shows its running weak but not actually pinking. JBS are supposed to be really good so will leave it to the experts I think :scratch: Thanks for your help guys will let you know whats up!!

[bruny 0]

Lamba probe is ok. Roll on thursday!

[CorradoVR6-Turbo 0]

how did you check it?

[Gareth_16V 0]

Hi guys, just my twopenneth, but an air fuel ratio of 14.7:1 is just the theoretical ideal mixture for a petrol engine. However, engines should not run at 14.7 as they will run too lean and damage to engine and wallet will occur. 14.7:1 is also called the Stoichiometric Air Fuel Ratio, and is also commonly written as Lambda=1. :dorky:

 

Lambda Value = Actual AFR divided by Stoichiometric Value. :dorky: :dorky:

 

Mixtures with figures less than 14.7:1 are considered to be RICHER than ideal. So your AFR at 13:1 is 0.89 Lambda, which is about spot on for max power. You should not do any damage running the car past 5000 RPM with this setup (provided everything else is OK of course....)

 

There are probably other reasons why you're not seeing the power you were expecting - remember rolling roads can only tell you what you're getting at the wheels, the power at the flywheel is just a guess, but that's a post for another day......

[bruny 0]

Lamba ckecked with engine running, terminal 4 [the single one] reading varying voltage between .4 and .8 volts :scratch: think thats right!

 

AFR @14.4/7 correct for light throttle but should richen up with harder throttle. Its just not delivering enough fuel. Pump, filter and pressure is good.

190 bhp @ the flywheel, it will lose around 18% through the drive and should result in 155bhp at the wheels.

The problem may be really minor [heres hoping] and I'm assured JBS are good with VW's. I will report back with the results on Thursday.

Thanks for the input guys, there's a wealth of knowledge out there :salute:

[bruny 0]

OK, nothing definative yet but codes showed maf and lamba probs which didn't return after clearing. Darren at JBS tested various bits and suspects faulty MAF. Reconditioned exchange units apparently not trustworthy. So biting the bullet have ordered a new genuine replacement £188 =vat :shock: ] to illiminate the possibility. Will check in 2moz or Saturday hopefully with fully restored power :D [Makes a mental note to stop spending so much in search of perfection :cuckoo: ]

[bigred 0]

did they check live data on a scope thats how we normally look for faulty maf sensor

[CrazyDave 0]

My 2p..... cam sensor. But check fault codes first :)

[bruny 0]

Just back from JBS, new mass air flow fitted, [ouch] but its cleared the error codes. However its still lumpy on tickover and lacking some punch. Suspect its still running weak but have not retested AFR to confirm.

The intake was removed for beadblasting a while ago so now thinking that there could be an air leak after the MAF meter. This could be allowing so much air that the ecu cannot compensate, resulting in weak mixture. Seems to make sense???

Failing that the injectors could be blocking up and not delivering enough fuel ??? [old fuel and standing for some time may be the cause of this] Fuel pressure at the rail is good!

No fault codes showing, no misfire, no smoking from exhaust, running out of ideas :scratch: Will check for leaks first before tackling the injectors :(

Any other ideas most welcome :salute:

[CorradoVR6-Turbo 0]

make sure the idle valve pot has not got a crack in it mate.

[bruny 0]

Will check it out as soon as I find out what it is, thanks for the tip :D

[CorradoVR6-Turbo 0]

Its next to were the throttle cable is black pot with pipes going fom intake pipe to idle valve,you cant miss it mate.

[bruny 0]

Thanks James, found it ,its cracked around the base. Blew up one pipe with the other one sealed, leakage big time. So this would draw too much air resulting in weak fuel mix, lack of power ? Will effect a temporary bodge and test reults! heres hoping that it has been the problem all along :D Top Man :notworthy:

[CorradoVR6-Turbo 0]

Thanks James, found it ,its cracked around the base. Blew up one pipe with the other one sealed, leakage big time. So this would draw too much air resulting in weak fuel mix, lack of power ? Will effect a temporary bodge and test reults! heres hoping that it has been the problem all along :D Top Man :notworthy:

 

good man! i always remove/bypass them,it made mine idle smoother... :scratch:

[bruny 0]

Definitely on the reight lines with this. Instantly feels different even with a bodged seal. Will order a new one assuming they are still available. Also found perishing on the underside of the joint of the main intake/ rocker cover pipe breather where it sits in oil.

Nice to have it sorted. thanks for the tip :clap: :clap:

[zak 0]

I think mine has the same problem, my cars overfueling and throwing loads of smoke out the exhaust. I had a look in the engine bay and i can hear a hissing noise from near the throttle body area.

[bruny 0]

I didnt have any smoke, infact no visable signs of a problem, just no real grunt. Couldnt here any obviuos leaks either. But having changed the offending item it feels far more responsive and fun to drive again :D Also seen a 10% improvement in fuel consumption :clap:

If you have excess air going in it should result in a weak mix, I dont think it would result in smoke emissions :shrug: