Bad VR6 Missfire (SOLVED!!!! - Dodgy no6 injector)

[was8v 0]

I've got a baaad missfire. Car is a 1992 VR6 with a dizzy and was in good condition before, plenty of power and nicely coloured spark plugs.

 

What a cylinder needs in order to fire:

1) Petrol and air

2) Spark

3) Compression

 

Pulled the plugs (mostly black indicating rich running) and number 6 is wet with petrol so cylinder 6 is missfiring.

Pulled lead number 6 and stuck a spare plug in it and its sparking when the engines on, no change in engine note.

There are no head gasket symptoms like mayo, pressurised coolant, smelly coolant, deposits on plugs or anywhere.

 

So the problem can only be:

1) injector stuck open (possible?)

2) Dodgy leads or plugs not allowing good enough spark

3) Blown headgasket just between 2 cylinders leading to poor compression.

 

When its missing theres a really nasty knocking noise from the engine at idle that disappears at higher revs. This came and went with the missfire when the missfire was intermittent. Hope thats not a dying bottom end.

 

I have a compression tester on the way and leads and plugs are easy to swap. How can I determine if the injector is stuck open? is this even possible?

 

Any other possibilities?

[Taggart 0]

How about the common bore wear in 1 & 6?

[was8v 0]

How about the common bore wear in 1 & 6?

 

humm theres no oil consumption or blue smoke which would indicate this - I guess the compression test would reveal and a leak down test confirm that.

 

Any ideas on how to test injectors?

[Kevin Bacon 5]

If you put a fresh plug in 6, does it then run OK?

 

If it does, it's oil on the plug rather than fuel.

[was8v 0]

If you put a fresh plug in 6, does it then run OK?

 

If it does, it's oil on the plug rather than fuel.

 

 

Nope - fresh plug comes out covered in petrol - this evaporates pretty quickly so I'm sure its petrol.

[Kevin Bacon 5]

Ah OK, that's good then, well, better than the oil scenario!

 

I suppose the next test is to move injector 6 to a different cylinder and see if the problem follows it.

It does mean taking the top half of the manifold off though, which is a pain in the behind.

 

Sounds like it's sticking open as you suggested. 100% open at idle would certainly extinguish the spark.

[was8v 0]

I suppose the next test is to move injector 6 to a different cylinder and see if the problem follows it.

It does mean taking the top half of the manifold off though, which is a pain in the behind.

 

I'll give that a go at the weekend, I guess the problem could lie with the ECU too sending an incorrect signal. Thanks.

[CorradoVR6-Turbo 0]

Have you checked for spark on the faulty lead? have you swaped over one of the leads to another cylinder?

[Kevin Bacon 5]

Have you checked for spark on the faulty lead? have you swaped over one of the leads to another cylinder?

 

Pulled lead number 6 and stuck a spare plug in it and its sparking when the engines on, no change in engine note

 

That's payback for the Demon Tweeks pic :lol:

 

Was8v - I have heard of injector drivers dying in the ECU, but it's very rare. If you swap injectors 5 & 6 over and the problem remains in 6, it's the ECU or wiring. If the problem moves to 5, it's the injector.

[was8v 0]

Was8v - I have heard of injector drivers dying in the ECU, but it's very rare. If you swap injectors 5 & 6 over and the problem remains in 6, it's the ECU or wiring. If the problem moves to 5, it's the injector.

 

Give me chance lol, all this having to be at work all day nonsense is getting in the way of messing with cars! Will have a go at the weekend, thanks for the help!

[Kevin Bacon 5]

What?? You haven't done it yet? Call yourself an enthusiast? :lol:

 

I was at work on New Years eve, got home, replaced a coilpack and some other stuff and was out the door to my mate's for NY drinks 2 hours later.....

 

Work, cars, social life, women...... they can all be done in the same day ;-)

[CorradoVR6-Turbo 0]

Lol i missed that one Kev:lol: Ive had injector ecu driver die on me before but you would know about it ! :lol: black smoke hardly would idle or rev and so on...

 

 

What?? You haven't done it yet? Call yourself an enthusiast? :lol:

 

I was at work on New Years eve, got home, replaced a coilpack and some other stuff and was out the door to my mate's for NY drinks 2 hours later.....

 

Work, cars, social life, women...... they can all be done in the same day ;-)

 

 

My hero :lol:

[was8v 0]

hummm how the hell do i get the injectors back in!!!!!

 

i removed them by pulling the fuel rail off, the injectors remained in the head, had to pull em out.

 

How do i get the thing reassembled?

 

I have fuel rail with injectors secured with tabs, but i cannot push the injectors back in! they are lubed up and i cleaned up the injector seats but when i push them in the fuel rail tabs just go upto the head!

 

any tips? special lube? lol

[was8v 0]

Right slavvered the lot in my girlfriends vaseline. One side has popped in but the other and middle ones still won't budge, will give it a go again tomorrow! Its scary how much force i need to use really!

 

I'm half hoping the problem is elsewhere so I don't have to take them apart again....lol.

 

Oh yeah while they were apart I measured their reistance, they measured around 17 ohms each, saccording to the bentley they should measure 15-21.

[Kevin Bacon 5]

16 - 17 ohms is bang on mate.

 

Yes, the injector O rings can be pigs when cold, but you'll find they slide right in when warm, LOL!

 

I use the old vas too, or grease.

 

I would soak the O rings in petrol for an hour to soften them up and if possible, warm the lower intake up :lol:

 

Sounds like a "right kafuffle", but it makes a huge difference. it's why I only ever do injector testing when the engine is hot :-)

[was8v 0]

Right not managed to get the injectors back in because I only had 30mins to mess with the car today. But my Draper compression tester showed up in the post.

 

I had to do the test with the engine cold as the injectors are still out, anyway here are the results:

 

Cyl      1      2      3      4      5      6
Dry    12.75  13.5    12    13.25    13   12.25
Wet    14.5

Figures in bar.

 

I only did cylinder 1 wet as I didn't have anything to get oil into the other cylinders without dribbling it down the aperture, 1 is pretty accessible.

 

The Bentley states when new the compression should read 11-13 bar and the wear limit is 7.5bar (with engine at 30 degrees F?)

 

This was with the engine cold - the figures should be lower for a cold engine as its not at tolerance temp?

 

So it looks like the compression is very good!? I'm a little puzzled as I would expect it to be a bit down since going by the state of the head bolts the head has never been off in its 110k life.

 

So I guess my problem MUST bethe injectors or some other chain in the fueling system? I suppose it could still be a poor spark but it looks damn good to me when I use a spare plug on a dangling lead.

[was8v 0]

humm just checked the bentley to see if my leads are going to the correct cylinder :? But its not shown anywhere.

 

Anyone have a diagram of which point fires which cylinder???

 

Also looking at the diagram attached I noticed the RFI cap that normally has cylinder numbers on it which I am mising and the rotor arm should have a screw in it - mine doesn't but is a secure fit on the dizzy.

 

Would these two missing cause me the problem ?! the dizzy cap also can be turned slightly (1 or 2 degrees) when clipped up - is that right ?!

 

These where both missing when the car was running right so I think i'm clutching at straws until I have the injectors back in.

[was8v 0]

Found out which cyclinder fires off which point on the dizzy - as you look at the dizzy its:

 

 6  3
2      5
 4  1

 

(Mine were on correctly)

[was8v 0]

Also noticed I'm missing the inlet manifold gasket between the upper and lower intake manifolds (upper no. 10).

 

Anyone know a source or part numbers? Cheers.

[CorradoVR6-Turbo 0]

021 133 227 J

[was8v 0]

^^^Thanks for the part no!^^^

 

Woohoo! it runs properly!

 

I've not updated this for a while as I've been waiting for some more injectors I got from someone on here. I was waiting because I didn't want to have to take it all apart again when I found the injector was faulty.

 

So re-assembled by cleaning the injector seats with a little wet and dry and greasing them up good and proper and they slid in nicely. As it turns out it only took about 10 mins to get it all back together (I didn't remove the inlet completely, I'd left the throttle and pipe work connected). I swapped by number 6 injector for one of the new ones.

 

Fired her up and all is well. Except the slightly stumbly idle - first step remove and clean the throttle body and ISV (tose bits I didn't remove above, lol)