Technical Fuel injection problem?

[derekbandit]

Fuel injection problem?
Help. My 2001 1.2 8vl Punto only runs on three cylinders when first started of if left for several hours. The problem disappears however after about 30 seconds running at idle and the car runs perfectly otherwise.
What’s happening? I feel sure it’s not an ignition problem.
Any suggestions welcome.
cheers

 

[Scoobysnacks]

Out of interest, why do you say it's not an ignition problem? It certainly sounds like an ignition problem to me! Have you replaced plugs and leads recently? I took most of the fuel and ignition system to pieces on mine recently, only to find the cause was a duff plug, for a similar misfire problem!

If it's definitely not plugs, leads or coil packs then maybe suggest a sticky injector.

Because it only happens at start up, it's going to be a piggy to diagnose!

 

[red]

Do you know which of the four pots isn't working on startup? (that's assuming for now that it's always the same one). If not, pull a plug lead before starting. If it fires on the other three, you have pulled the duff one. If it won't start or tries to run on two, you've pulled a good one.

Now you can swap things like plug and injector to another pot to see whether the fault moves. If you're going to play with injectors, remember to depressurise at the Schrader valve first.

red

 

[Scoobysnacks]

I was thinking the same, but the op says that it only happens for a few seconds after start-up. Not sure if you'll have time to start pulling plugs etc.

 

[red]

OP said about 30 secs for fault to clear. I suggested to pull a lead before starting up. He could tell in a few seconds whether it was now the same (running on three) or worse (running on two or not at all).

red

 

[Moosey]

Out of interest, why do you say it's not an ignition problem? It certainly sounds like an ignition problem to me!

I agree with Scoob. Sounds like ignition to me too. Coilpack or plug maybe. Coilpacks are often affected by heat on the way out. (Including heat inside them.)

If you're going to play with injectors, remember to depressurise at the Schrader valve first.

Sound advice. If you do go pulling/swapping injectors, do as Red said and relieve the pressure in the rail first. You can get a little bottle or cup and position it so it sprays all the petrol into it, and not anywhere else.

 

[derekbandit]

Hi. Many thanks everyone for your interest. I'm going to start pulling injector leads on Saturday to find out which pot it is. Should not take too long as the problem now occours if the car is just left for 15 minutes or so although it still clears within the 30secs.
I don't think it's ignition because in my expierence faults with plugs, coils, leads etc. normaly occour under high load/wide throttle openings.
More comments very welcome.
cheers
derek

 

[Moosey]

Don't pull injector leads! Pull the HT leads to check while cylinder is misfiring.

And why are you ruling out ignition? Ignition problems can happen at any time. Hot, cold, right after running, when left sitting, high revs, low revs, etc..

Find out which cylinder is misifirng, check all ignition parts. If you think they're all fine, then pull the fuel rail and swap injectors over, see if the misfire follows the injectors. If it doesn't, it's unlikely to be injection.

 

[Scoobysnacks]

I would say that it's perfectly possible for it to be an ignition problem. Mine did exactly the same thing, started rough as rats, sounded like a diesel, for about 30 seconds then ran fine. Mine also misbehaved at high loads, but keeping the revs up made it behave!

Even if it is a fuel problem, pulling the plug leads will allow you to identify which cylinder the fault lies in, and then you can start swapping components over to find which is the issue!

 

[Moosey]

Also, pulling injector leads will most likely cause the ECU to log a fault code.

Yaaaaaayy.. engine warning lights!

 

[derekbandit]

Progress update.

More confused than ever now.
Took your advice and pulled plug leads. It’s no.1, [the cam belt end]. I swapped spark plugs, leads and coils. No change. Then I swapped fuel injectors but still no change! It’s still no 1 cyl. that doesn’t fire for the first 30 seconds or so. I’m baffled.
Two things I noticed: 1/ when I saw the injectors I felt sure that would be the problem as no 1 appeared to have tiny specks of corrosion on the face. 2/ the no1 spark plug was slightly darker in appearance than the others.
Car still in use and running fine otherwise.
More suggestions please.

 

[Moosey]

Compression test.

 

[derekbandit]

progress update


Well, situation resolved, almost. Discovered I was low on coolant level and the penny started to drop. Then the next time I went to start the car it didn’t crank at first. It’ s got to be coolant leaking into no.1 cyl. Head gasket I guess.
Just dropped it of at garage as I don’t have the facilities here to remove the cyl. head.
Many thanks for your interest. If anything unusual is found I’ll post it