Regular missfire on LPG, not on petrol

[Chris740R]

I've got a regular missfire on cylinder 1. It exists on gas but not on petrol.

I narrowed it down to cylinder one using the lpg software, switching individal cylinders between lpg and petrol till I found the affected cylinder.

I've tried swapping HT leads which has made no difference and I have a replacement set of spark plugs which I'm going to try. Tonight I'm also going to try swapping LPG injector hoses on the injector rail to see if it is a problem with one of the LPG injectors.

Is a faulty injector coil a likely reason, and if so is it possible to buy an invidiual replacement coil or should I replace the entire rail?

The injector rail (I think) is a 'rail IG1'

[capt jack]

You've done quite a bit to narrow down the problem.

I'd say that either the plug on No 1 cylinder is dying (LPG exposes ignition problems more than petrol does) or the LPG injector to that cylinder is faulty in some way.

Of the two I'd be more likely to suspect the injector as it's so regular and definite.

It could also be that the LPG supply rail is blocked just before the gas gets to the injector.

What type of injector is fitted?

The ones I had on my conversion were simple solenoids, dead easy to take apart and clean.

You shouldn't need to replace the whole rail. Can you post up any pictures? I have some solenoids spare from my old car - you never know - it may be the same!

Cheers

Jack

[classicswede]

The Rail injectors are easy enough to take part. It is most likely the rubber stop that come unseated or torn causing irregular fuel delivery on the cylinder. If you swap the hoses over on cyl 1 and 2 that should move the fault. If it stays on cyl 1 swap the plugs over on 1 and 2. If the injector is at fault it will then move to cyl 2. If it moves at the point of swapping the pipes then it could be a blocked pipe or another problem related to that cylinder.

As your engine is full group it does not matter what lpg injector goes to what cylinder

[Chris740R]

Ok... well it seems that the misfire comes and goes, because when I went out to go and fix it, it was nowhere near as pronounced as it was earlier today.



I tried:
swapping injector coils on cylinders 1 and 2 - made no difference
swapping hoses on cylinders 1 and 2 - might have made a little bit of difference
swapping and checking gap on spark plugs on cylinders 1 and 2 - might have made a bit of difference.

It seems to be a smoother now, earlier on it was a definite miss as if one of the plug wires was missing. I guess I'm going to have to wait and see if the problem resurfaces tomorrow. At the moment it does seem like cylinder 1 is getting a weaker spark than the other 3 cylinders and its working on petrol but sneezing on lpg.

[Rversteeg]

Not sure what engine you are referring to, but looking at your name I guess it is a 2.3 l red block.
Running on LPG requires a stronger spark than petrol, so this might be the first sign of the ignition getting weaker. Besides looking at the LPG system, I would also check the ignition system. Check the distributor cap for signs of wear or cracks, or oil contamination (worn seal). Not expensive, so replace if suspect.
Check spark plug cords, try spraying with water (I had a failing ignition coil cord, but only after the engine had heated up in rainy weather. Towed off twice before I discovered the problem). Or simply replace, same for spark plugs.
I don't know your LPG system, but about petrol getting into the inlet manifold while running on LPG? The Vialle LPi system for example has a relay which is supposed to cut the fuel injection when running on LPG, but the older versions of this relay are known to fail after a while (pull fuel injector connector when in LPG mode, should make no difference). Also check the petrol pressure regulator. If the membrane is cracked, petrol can enter the inlet manifold through the small rubber hose.

[Chris740R]

So an update:

The misfire does exist on petrol after all, but nowhere near as bad. It can be identified as a sneeze rather than a complete lack of firing.

The distributor cap, plugs and leads are at most 10 months old. The cap itself looks fine, the gapping on the spark plugs is 0.7-0.8 and I've swapped the leads with some new ones, with no difference in results.
Using a spare spark plug I have looked at the spark from each lead when held against the engine block, and all cylinders look the same (white/blue spark).

I have fully removed the LPG pipe to cylinder 1 to check for blockages, it flows feely with no obstructions.

I'm going to have a look at the distributor now to see how it looks.

As an aside, the head gasket has also been replaced (November time) and during the replacement, the head was checked and all the valves were found to be fine. I re-did the valve shims too. I'm wondering if the shims have settled and need re checking. I have a compression tester that I can try out tomorrow to see if its due to a lack of compression. The car uses very little oil and I haven't had to fill the coolant reservoir since the gasket change.

[Chris740R]

More update:

Things checked:
1) Spark plugs - gapped to 0.7-0.8
2) HT leads
3) Distributor
4) Gas injector (solenoid valve, pipe and injector nipple)
5) Fuel injector - no fuel is leaking past the injector.
6) Fault codes on obd - nothing logged

Things not checked yet:
1) Compression in cylinder 1 (I'm thinking valve shims might not be right, I'd prefer to think that the gasket hasn't gone again...
2) Fuel pressure regulator

anything else anyone can think of?

[classicswede]

do you want a set of injectors to try

[Chris740R]

Hi Dai,

That would be great, I did some more diagnosis today. I found something interesting about the software I'm using (EuropegasMini). I have been using the injector pane to switch on and off different injectors. I thought this was working as I expected, however it seems that if I deselect injector 1 (and only injector 1) all 4 injectors go back to petrol. Even though the injectors fire together as a batch, I thought I'd still be able to select one at a time and toggle it on and off.

After I realised this, I ran it on LPG and unplugged each LPG injector one at a time. Injector 1 - idle gets worse (a surprise), Injector 2 - idle gets worse, Injector 3 - no change to idle and injector 4 - idle gets worse.

So! I dismantled injectors 1 and 3. One difference I could see was that the rubber o-ring was worn down in the end of the injector 3 piston (looks like it acts as a husher or damper). The picture below shows the part (not the separate O-ring).



I then moved the piston and housing to a different cylinder position on the injector rail, and the misfire followed. The injector is also a great deal louder than the other 3, although it always seemed to be this way.

So Dai, if you have them available or can point me to a retailer, a kit (might as well do all of them) would be great. If I can get it running again properly before the weekend that'd be fantastic.

[Chris740R]

Morning Dai

Thank you for the spare injector rail, it arrived on Saturday morning, I swapped out the bad piston and now the car idles well again.