Mi Misfire On Idle - Intermitant Mis On Load

[Rom 0]

Hi guys. A little history first. I've got a 1.9 Mi running 2 row mi ecu etc. Rebuilt appeox 10k ago.

 

It developed a bit of a misfire on load, which would clear around 3k. I changed the plugs as they were pretty old, but to no avail.

Tried leads, no change. Another ign amp ( non Bosch ) got worse. So swapped back.

All plugs are sparking through the leads. And pulling any lead off makes the idle worse.

 

Not sure what injector resistances should be, but they were all 0.2, which would indicate no one is out from the others.

I've been messing around this week on lunch times, the idle is still rough, but not a constant 3 cylinder running. More like a lumpy idle from a cam. Timing has been checked and is ok.

 

I took it out last night, and it didn't mis while driving. It had been horrendous pulling away from junctions etc, proper kangerooing.

 

I'm going to do a compression test at lunch today with it warmed up and WOT.

 

Any suggestions on what to check would be great. As I'm kinda just going round in circles !

[Veero 1]

Could be a few things, have you checked the TPS is working to sense what throttle is being used? It may click just as you move it off the stop but if the resistances aren't changing it won't be fuelling right which may cause the kangarooing.

 

I had, and still have to a degree, a misfire on idle, but after replacing plugs, leads, coil, arm and rotor and then finally a known working used ignition amp it is much much better and now only misfires occasionally, so it hasn't solved it but is working much better.

 

Even though the injector resistances are the same have you had them reconditioned or at least flow tested?

 

Try cleaning out your ICV with carb cleaner, for some reason it made a huge difference to my low speed pulling away and idle speed.

[Tom Fenton 1,542]

Have a look at night, sounds like classic plug lead going down to earth somewhere you can't see. How old are the leads?

[Rom 0]

Veero..

 

Any idea what the resistances / pins are for Tps checking are ? I've not done that yet.

 

The injectors were refurbed when I built the engine, print out was fine. It's always run on V Power with cleaner at regular intervals, though of course that doesn't mean they can't be broke !

 

I've not cleaned the Icv for about a year. It doesn't mis if I unplug it on idle, but I think that's just because the idle is being raised to about 1200 to compensate ? I'll give it another clean though.

 

Tom...

 

The leads are about 3 years / 10k. Some silicone jobbies. 2 are f***ed, and I've had to terminate the ends. But I did try some other leads I had lying around, and there was no change.

A new set are on the list, but I'm broke as a joke right now, so need to be 100% what I'm buying is the cause.

[24seven 104]

The throttle position switch is just a switch on these, not a full range potentiometer (it switches at idle, part load and wide open). As long as it clicks as soon as it rotates it's usually fine. The voltages/resistances you should get from it are below. You don't need the engine running to check these, but I did find it easier to check them at the ECU.

 

 

 

 

 

 

 

I've been having the same problem. constant misfire at idle and bad kangarooing at part throttle/cruising steadily. Under acceleration load it's fine. Recently I had to change the exhaust manifold gasket which cleared up the problem quite a lot, which really surprised me. As you have I've changed the plugs, leads, coil, amp and I've also changed the dizzy cap, rotor arm, ICV, AFM, coolant temp sensor, TPS and cleaned up the butterflies in the throttle body, but it's still there. Next on my list is to get the injectors cleaned and replace the crank angle sensor.

[Rom 0]

Thanks for those mate, much appreciated.

 

Under proper acceleration it's fine, but normal light throttle 2-3k can be really bad. It was fine last night on about a 5 mile test drive.

I did notice this week it's been hard to start, needing throttle, and the odd stall. It's back to normal now the misfire has gone.

Right now it's just the idle mis I've got, but I'm not convinced the load mis won't come back...

[24seven 104]

exactly what I've been suffering. I find that using 97/99 ron fuel smooths it out a lot, which is partly what makes me think the injectors may be to blame for mine.

 

If you go into the "Aftermarket Engine Management" sub forum you'll find the program I used to get those screengrabs. It's basically a complete diagnostic manual for the Motronic 4.1 system (2-row).