Rough running and completely stumped!

[Flo 0]

Good evening all! Had a 'rado for year and half now, and have to say, been reading this website for a while now. Love it and extremely useful!

 

However, I'm hoping someone can help me.

 

Had some very erratic running recently, the car was idling badly, losing power and 'coughing' through the rev range. changed the coil pack, Leads, plugs and the front engine speed sensor (It was the one just above the sump at the front, I think thats what it is). Afterwards it felt back up to 95% of how it was running.

 

However, there is still a slight misfire. although it doesn't jerk the car, you can feel it throught the steering wheel and seems to lose power periodically. :x

 

VAG 1551 came up 'knock sensor open/short circuit' and 'engine speed sensor - no signal'. I think we unplugged the knock sensor connector tabs and cleaned them up, which seemed to help a bit. but anyone know where the knock sensor is?

 

but i'm such a perfectionist i cant help but notice the slight loss in power and very slight misfire. even at idle, you can feel it through the steering wheel.

 

Cylinder 2 and 4 have 0.6 and 0.7 bar of pressure and the other four are at 1.2bar. could the loss in compression be causing this? is it time for a rebuild? 94K on the clock. :?:

 

any suggestions would be greatly appreciated.

 

Many thanks in advance

[Roger Blassberg 0]

My VR6 idles a bit unevenly, and apparently so do those of others

 

I'm a bit confused by your compression pressures. The pressures should be in the order of 9 -10 barg (bar gauge = pressure above atmospheric), around 150 pounds per sq. in.

 

If those two adjacent cylinders are so far down compared to the others, I would begin to suspect that the head gasket is leaking between them. Alternatively you may have an issue with valves not seating or there is excessive clearance between rings and bores. Is there excessive oil consumption or lots of smoke under acceleration? Try squirting some oil into the offending cylinders and re-testing; if the pressures come up to the results of the others, it looks like bores.

 

Are you getting any other head gasket symptoms, such as loss of coolant, oily water, watery oil (mayonnaise in the cam cover, emulsion on the dip stick), or excessive pressure in the cooling system? Even if not, there could still be a dry leak between the cylinders.

 

There are 2 knock sensors on the VR, low down on the block near to the mountings, one front and one back. They are a bit of a bar-steward to get at. Check the wiring continuity and that the through-bolts are done up to precisely the right torque (15 lb. ft IIRC), otherwise they don't function correctly. You havn't mentioned pinking, so probably there is no problem there.

 

Best wishes

 

RB

[Kevin Bacon 5]

My head was rebuilt at 94K as she was just starting to use a wee bit of oil. This restored midrange power and along with a complete chain overhaul (using the Solid tensioners off a MK4 12V) the engine's silky smoothness returned too.

 

I agree, your compressions are confusing. If they we're 1.2 bar, the engine would even run or it would give you about 14 hp. Or where they *reduction* in compression figures?

 

I also have a rough idle, despite all that work and being told the bores were fine when the head was off. So don't chase your tail trying to sort an idle issue. VR6s just idle poorly, period. Always have, always will. I've driven a variety of VR6s from 45K to 145K and they're all the same!

 

I've aquired a set of injectors and a new rail, so I'll be sending them off for balancing and ultrasonic cleaning. That will restore the correct flow pattern and flow rates and who knows, it might even improve the idle! Yeah right! But as I got the whole rail and squirters for £40, it's worth a go.

 

K

[Flo 0]

thanks for the responses guys.

:D

 

took it on a long run today and seemed a lot better when i got back. I live in central london andI do mostly town driving. i think she enjoys getting a damn good thrashing when i take her to the countryside, I certainly do anyway!

 

I havent noticed any excessive oil consumption and the coolant is absolutely fine and actually, this is making me even more worried. valves sound expensive and bores even more so!

 

Vince at Stealth mentioned 2700 + vat for a full rebuild, but ive got to make the painstaking decision whether or not to keep her. put the money in to keep her going as she should or cut my losses and get something else. she's costing me an arm and a tit!!! :mad:

 

Also, i'm not too sure what pinking sounds like. ive never heard it before, i dont think.

 

once again thanks to those who responded.

[Roger Blassberg 0]

as Kev said, it may be that those figures were reports of discrepancies from the normally-expected figures for compression. 1.2 bar is about 18 psi, which on a 94K engine wouldn't be unusual in my opinion. If it runs as well as you say, and doesn't use much oil, then it's probably ok.

 

Pinking, also known as knocking, is a light high-pitched metallic sound from the engine, which indicates pre-ignition. You can't miss it, and is most likely to be heard under moderate to hard acceleration.

 

It's caused by a number of things, such as using fuel of a lower than specified octane rating, carbon deposits in the combustion chambers, or over-advanced ignition timing. Your car will almost certainly have an ignition system which cannot be adjusted other than by the sensors in the engine, including the knock sensors. They detect the onset of pinking and send signals to the ECU to retard the ignition to a point where it stops pinking. If they are faulty or are incorrectly installed, it will pink. You need to attend to it at once because the pistons could be damaged otherwise.

 

Get the wiring to the sensors and the through-bolt torques checked. If that doesn't do it, have the sensors changed.

 

Yes, Corrados cost money to keep going but if well maintained they are appreciating in value, as opposed to the barrow-loads you lose in depreciation on more modern cars. Best of all, you get to meet such nice people on the forum !!

 

Best wishes

 

RB

[Flo 0]

FIXED!

 

just thought i'd let you all know that the problems got worse and worse. Finally found what was causing it.

 

Two wires were chafing against each other on the main engine wiring loom and shorting out! one of which was the throttle wire!

 

got them stripped back and reinsulated and now shes purring away like a kitten again!

 

thanks christ for that!!!! 8)

[joebrent 0]

I love it when an irratating problem finally gets fixed!!! Now go out and enjoy the weather in your car....well if the sun roof works that is!!!

[craigowl 0]

Two wires were chafing against each other on the main engine wiring loom and shorting out! one of which was the throttle wire!

 

Let's know where you found the chafing wires Lloydieboy79 - us other 1995 VR6 owners will know where to look if we get your problem in about a year's time!

Thanks in advance.

[Flo 0]

On the main engine loom (coming in to the engine on the top right hand side, looking at the front). the non-engine side of the harness, only about an inch from the connector. Its just a mass of wires and when we jiggled them about, you could see sparks tracking out across the loom and the engine went nuts at the same time.

 

separated them all and cleaned them up, then could see which ones had chafed. reinsulated them, tidied them all back up and hey presto! My mechanic did all the work so i'm afraid i couldn't tell you exactly how he did it, but my guess is that he used heat shrinking wire insulation.

 

hope that helps anyone who may get this problem. trust me its bloody irritating as it comes up on the diagnostic computer by showing up as a dozen or so sporradic faults with various sensors and doesn't help you narrow it down at all!

[STORM 2 0]

An example of the limitations of VAG-COM perhaps?