VR6 Hesitating / misfire at low revs [now fixed!]

[CorradoWannabe 1]

The car is a 1995 VR6

 

I've done some searching around on the forum and learnt a lot - but i just want to get some views before i invest in a new fuel pump.

 

Here's a detailed description of the issue - some of these points may be red herrings:

 

- Unfortunately allowed the fuel level to get very low then filled up with a full tank of BP unleaded [normally i only use optimax]

 

- 11 miles later whilst driving on the motorway at about 70mph the car started to lose power, then was jerking around like a kangaroo! Pulled the car on to the hard shoulder - turned it off and on again and then it seemed better.

 

- Drove another 100 miles that day, mainly motorway driving with slight hesitation esp when starting in first gear and also with low revs in second gear - car pulled and ran fine for most of the journey.

 

- My friend who was in the car during all this said he'd had the same issue on his golf 16v and injector cleaner had helped.

 

- Next day replaced the fuel filter and tried again - still serious hesitation to the point of almost stalling when pulling away. Once above 2500rpm power is good.

 

- Then added injector cleaner which made about a 50% improvement with this issue - hesitation felt far less. But still present - also at high revs (4000/4500rpm) in 4/5th hesitation is felt.

 

 

I think its the crap at the bottom of the fuel tank getting in to the fuel system. I had hoped the cheaper options of new fuel filter and injector cleaner would cure it - but its still there.

 

Would adding injector cleaner again to the next tank full be advisable? Or is it bad to use it too often?

 

Does it sound like the fuel pump is on its way out? Is there anyway to diagnose this before i pay for the fuel pump to be replaced?

 

Could it be something else such as spark plugs?

 

Any help appreciated :roll:

 

I should add that the idle is very stable and smooth - it idles happily at about 600rpm and also the car fires first time without issue.

[veeDuB_Rado 0]

Could possibly change the fuel filter..

[CorradoWannabe 1]

The fuel filter was changed, but didnt fix the issue unforunately - i had hoped it would as i knew the filter hadnt been changed in a while..

[dr_mat 0]

Original fuel pump? On 230,000 miles?

It's funny that you have problems at low revs though, I would expect a poorly fuel pump to cause bigger issues at high revs due to not being able to sustain a flow rate. Sounds more likely that you've got crap in your injectors, or of course, you might have something more fundamental (and the running out of fuel was a coincidence).. Does it use oil/water?

[BlueRado 0]

I had a very similar problem to this when I first got my car. As I'm useless, I took it straight to JBS who diagnosed a faulty fuel pump relay - might be cheaper option than a new fuel pump?

[CorradoWannabe 1]

dr mat - pretty sure the fuel pump has been changed before - i'll check the history tonight - it doesnt use oil / water much at all [much better than my 16v corrado].

 

What is the best way to remove the crap from the injectors - is it ok to use another load of injector cleaner in the next tank of fuel? Another ways to clean them more thoroughly?

 

Fuel pump relay is a cheap and easy thing to rule out so i'll give that a try too - thanks BlueRado.

[Trig 0]

I would of said check the plugs but you say it is idling ok so perhaps not, is it definately idling ok? Harder to notice if the car is misfiring with 6 cylinders.

[CorradoWannabe 1]

The idle seems fine, its mainly when i start to drive off from stationary or when accelerating in a high gear with low revs that the problem manifests itself.

[Roger Blassberg 0]

I would suggest a change of plugs and leads. I had similar problems, not as bad as yours are described admittedly, but a definite misfire and hesitation under load at low revs and a perfectly smooth idle (at least as smooth as can be expected from a VR). New plugs and leads transformed the whole experience.

 

Best wishes

 

RB

[Dutch24V 0]

Sounds like it could be a plug to me.

 

I've just replaced plug 6 due to the exact same symptoms. Once the engine is reving over 2500-3000 rpm it's not as noticable, but below that on load big hesitations.

 

I have to change plug 6 every 10000km's or so due to a knackered engine and the symptoms you describe match those to when as the plug is just starting to fail.

 

Dutch

[CorradoWannabe 1]

Thanks for the advice guys - going to change the relay and put in some new plugs and then i'll report back .. also put in some optimax next fuel tank and add a bit more injector cleaner.

[STORM 2 0]

Yep = plugs+leads first, but as youve probably seen during the search, there are a million plus reasons for this kind of behaviour. I would get it hooked up to VAG-COM, because a damaged coolant temp sender or similarly a damaged cam position sensor (both easy and cheap to replace) with play intermittent havoc with fuelling and the car will hiccup.

I've been down this road, unfortunately and its best to exclude an easily diagnosed sensor fault and get it over with quickly. My problem was the cam position sensor in the end

[CorradoWannabe 1]

UPDATE:

 

Only had a chance to put in some optimax and more injector cleaner to date but got some more information on this issue.

 

Now even if the car is sat stationary and idling and i apply acceleration you can sometimes feel very bad misfiring.

 

Its so bad that sometimes upon applying acceleration instead of the revs going up they move down below idle level and the engine almost dies.

 

Here's a link to a video of it - the quality is bad its too dark and its an mp4 file which most people cant see but if anyone can and can comment as a result of what they see it would be great:

 

link to video - needs quick time installed

 

In the video the car is idling at 700rpm ish - each time i am just applying the accelerator about 1/4 down and holding it there - once revs over 1500rmp i let it drop to idle and repeat.

[Trig 0]

Sorry dude that could be a video of my mum farting for all i know, but I would suggest a change of plugs and leads. :D

[dr_mat 0]

Really sounds like the MAF to me. Maybe it's on the way out ...? Mine does exactly that if I disconnect the MAF.

(Funny, I got no sound in that video, think my player is too old ..)

[CorradoWannabe 1]

Thanks dr mat - interesting idea - an induction kit has been added fairly recently MAF may have been affected at this stage or may just be on its way out - i'll try disconnecting it and see if its different.

[dr_mat 0]

Once it's disconnected it will probably run rough for a while, but once the ECU realises it's totally fubar, it should fall back to using the throttle position (assuming that sensor is working ok!) so the car should be driveable, if not perfect.

[CorradoWannabe 1]

Dr Mat - i owe you one! The problem is now sorted without having to spend any extra money too.

 

After you mentioned the MAF myself and my dad decided to take it off and clean it etc - upon doing so he noticed this:

 

 

The wire at the end had broken off - maybe due to age + vibration from the induction kit which was loose for a while.

 

Neway - after using a pin + solder and some inventing thinking managed to get a good connection and tape things back up (temporary fix) and took it for a drive - car is fully restored to its former glory!

 

Thanks to dr mat - you saved me lots of £££ - this forum has another happy ending :) i'll be sure to increase my standing order payment accordingly!

[dr_mat 0]

I accept all major credit cards ... :)

[Roger Blassberg 0]

I do like a happy ending !!

 

As a slight aside, is there a "proper" way to repair this type of broken connection; in other words, are these moulded plugs amenable to being taken apart so that the wire can be soldered or crimped back onto the back of the pin? Or is there perhaps a replacement type of plug which can be bought which can properly connected to the wiring loom?

 

The most extreme example of these connectors is the one to the ECU, with a huge number of wire terminations; how would that be repaired if a wire breaks off right at the back of the pin?

 

I feel an RW1 moment coming on..........

 

Best wishes

 

RB