19 replies to this topic

[Matty_Lib]

Hey guys,

My names Matt, first topic on SC but have been lurking around here for a year or so.

Anyway, I have a 92 Liberty RS. And as of late, its had an issue with it that I can't find an answer to..

Basically, the car is running on 3 cylinders. Only problem is, its getting fuel, and spark, and everything seems in order, it just runs on 3 cylinders. However, if I unplug the AFM and start the car, it will fire up all 4 cylinders and idle smoothly, wideband says its mega rich (expected) but its all running. If i plug the AFM back in while the car is running, it will drop the cylinder (No1) again, and go back to running like a POS.

I've tried 3 different working AFM's, checked for codes and reset the ECU multiple times. Also, before I decided to unplug the AFM I had changed the injector and coil on No1 cylinder, checked for vacuum leaks, checked FPR, and basically inspected every hose, connection etc in the engine bay.

Mods on the car worth mentioning;
FMIC
Parallel fuel rails
Standard 380cc injectors
Bosch coils
Sard FPR, set to 38 PSI
V2 STI ECU with Prova Nurburgring chip

Can anyone shed any light onto my situation? I have no idea what to check next.

Cheers, Matt

[Sam]

Its not a spark plug or something simple like that?

[Matty_Lib]

Nah man, have checked all that

[Cam.]

Do you have access to a scan tool?

When did the issue first happen?

How do you know the other AFM's are working correctly?

[Matty_Lib]

Don't have access to a scan tool.

The 3 cylinder issue started after a replaced an injector that wasn't working properly. I put a new one in and then it started playing up and running rough, I put the original injector back in but didn't make any difference. While checking injectors and leads I noticed it was running on 3 cylinders. Then I eventually got the shits and unplugged the AFM and started the car and all 4 were firing.

The 2 other AFM's were off other cars that were running fine and throwing no codes etc.

[Alex]

Dud coil pack?

Have you pulled out the plugs to see which cylinder is not firing?

[Matty_Lib]

All coil packs are getting power, and sparking. The cylinder that isn't going is the drivers side, front cylinder (cylinder 1 I think). I pulled out the plug to make sure it was sparking also and it is. How I first figured it was running on 3 cylinders is, I unplugged power to each coil, and when unplugging the coil to cylinder 1, there wasn't the obvious sound of it dropping a cylinder.

It just confuses me how it will start and run on all 4 if I unplug the AFM, but as soon as I reconnect it, it will go back to running on 3. :S

[Alex]

What coils are you running?

Coils can be receiving power ok, but can drop out under load.

[Matty_Lib]

I was running WRX coils, now Bosch HEC-715. The issue was present with both coils. I wouldn't think there's much load on them at idle? Could it be ignition related or something?

[RX25SE]

Have you checked for a vacuum leak around no 1 ?
Is the seal at the base of the injector fitted correcly?

[tmh983]

as rx25se says. If there is a vacum leak, even a small one around the injector then it won't deliver the same quantity of fuel per pulse.
Get some brand new o-rings, and make sure you lubricate them before pushing the injector in, its very easy to tear the o-rings when you push them in. and cause a vacum leak.

Another thing you could try is swapping injectors for 2 cylinders and see if the problem stays on number 1, or follows the faulty injector.

[Matty_Lib]

I've tried swapping injectors over, and also fitted other injectors and had no luck. I lubricated the o-rings when fitting them and I'm pretty certain they are all sealed fine.

Can anyone explain why it's only happening with the AFM plugged in? That part is what's confusing the sht out of me.

[RX25SE]

The ECU lengthens the pulse with of the injector.

Im still going with a vacuum leak as the will compensated for by the extra fuel.

Could be a vac leak upstream from the injector. Check all vacuum hoses and fittings.



Aslo, with the engine running like a dog, spray carby cleaner around the inlet gasket, injector, hoses etc and listen for a change in the idle quality. The carby clean will be sucked in through the leak..


If you can get your hands on a ocilloscope (or even a good scan tool) check that the pulse witdh of no 1 injector is the same as the other three. I'll guess that 2- 3.5 milliseconds is about right.

I do recall the standard Gen1s having a fault with the (I think) canister purge relay. For some reason this would cause the no1 injector to run at half duty cycle causing a rough idle. More of a partial miss rather than a dead miss though.

[Matty_Lib]

Cheers for the help mate, I'll go over it all tomorrow and see where I end up.

[Matty_Lib]

So I triple checked all hoses and fittings, also checked with carby cleaner, pulled out the injector and resealed with new seals. No difference

[RX25SE]

I think this is now beyond internet diagnosis unless you can get your hands on a gas analyser and/or an ocilloscope.

Perhaps check for voltage drop across the injector power supply wire to cylinder 1 ?


If it runs OK when rich and the fault stays at no 1 with coil and injectors swapped around and no vacuum leaks, I would suggest that the no 1 injector is not recieving the correct signal.

Would you happen to know how the injectors are fired?
ie: synchronous (all at the same time, I doubt it but may run this way on cranking), grouped (two groups of two, my guess is this) or sequential (follows firing order).

Its not a spark plug or something simple like that?

Nah man, have checked all that

Did you swap plugs around?

[Matty_Lib]

Yeah have swapped plugs around, will get back to you on the rest. Thanks.

[Nicko_]

What did you end up finding as the problem matt ?

[Matty_Lib]

A big part of it ended up being a combination of a leaking injector(s) and AFM. Runs better now, but not the best.

[Nicko_]

Yeah I always did forget to ask you