Misfire hell

[purpleliability]

Right, I need some more help chaps!

I had the car over at Emerald for a new ecu on Friday (fantastic to deal with and a superb service) and unfortunately it seemed to misfire at anything more than 25% throttle. It did this on the MBE and Emerald so it isn't ecu I related.

I replaced the plugs and leads about 400 miles ago and replaced the coil packs today. Unfortunately, same issues now.

The injectors were cleaned prior to the remap and Emerald are confident that it is an ignition related issue.

The car runs perfectly at light throttle loads,very smooth, it's just when the throttle is increased. I am going to wrap the HT leads after the car has cooled in insulation tape and double check that the leads are secure, any other suggestions?

I am getting close to the end of my tether now..... Thanks!

[ridds]

Throttle pots. See what values they return, if they bounce around then they are shot.

[ridds]

Throttle pots. See what values they return, if they bounce around then they are shot.

[purpleliability]

Fitted a new pair and they track perfectly. I managed to find a split in the HT leads so I am just going to bin them and buy a new set.

[Gazzab]

Are they magnecor leads!? If so bin them and get standard cerb items. Are the coil packs Bosch items?

[G9RGE]

Also have a look at the join where the engine wiring harness goes into the car. Mine needed a good clean, I tried everything before hand, leads, ignition module, plugs , coilpacks, and throttle pots and still had the same misfire. One of the coilpacks wasn't getting the correct voltage, I was pulling my hair out and it turned out to be a bad connection in the round block.

[purpleliability]

G9RGE said:

Also have a look at the join where the engine wiring harness goes into the car. Mine needed a good clean, I tried everything before hand, leads, ignition module, plugs , coilpacks, and throttle pots and still had the same misfire. One of the coilpacks wasn't getting the correct voltage, I was pulling my hair out and it turned out to be a bad connection in the round block.

They are standard Cerb leads from Racetech, will try some new ones today.

Thanks, I will take a look at the harness today as well, appreciated!

[TimJM]

I'm guessing you have checked the obvious - lambda, coil packs and timing?

I had exactly the same as you on my Cerb a while back and one lambda was down and the timing slightly out.

[spitfire4v8]

Cant you at least isolate it to one bank by running it under load with the dyno lambda probe in each exhaust and watching the mixture? That way you're only concentrating your time on the bank with the problem ..

[purpleliability]

Ok, I have checked the loom connection and cleaned it with contact cleaner, replaced all 8 leads and plugs and it is still missing under load and 25% or more throttle.

I had the lambda's checked before I went to Emerald and also replaced both throttle pots (Castle Lotus and TVR ran it on the diagnostics port on the MBE and found no issues).

Would fuel pressure cause something similar? It seemed to start misfiring not long after I had the injectors cleaned, I am literally tearing my hair out now!!!

[FarmyardPants]

I'll vote for HT leads

[TimJM]

purpleliability said:

Ok, I have checked the loom connection and cleaned it with contact cleaner, replaced all 8 leads and plugs and it is still missing under load and 25% or more throttle.

I had the lambda's checked before I went to Emerald and also replaced both throttle pots (Castle Lotus and TVR ran it on the diagnostics port on the MBE and found no issues).

Would fuel pressure cause something similar? It seemed to start misfiring not long after I had the injectors cleaned, I am literally tearing my hair out now!!!

Have you checked the regulator (i think that is what it is) iirc brass coloured round dome at back of fuel rail. After some work on my cerb a garage put in the wrong one and that was very lumpy and misfired.

[purpleliability]

TimJM said:

Have you checked the regulator (i think that is what it is) iirc brass coloured round dome at back of fuel rail. After some work on my cerb a garage put in the wrong one and that was very lumpy and misfired.

Has anyone got a picture to hand of it the right way round so I can check please? Thank you!

[Tanguero]

I am fairly sure it will only fit one way round

[Mags]

Long shot but if you have disconnected the injectors are they plugged up in the correct order, mine weren't and it misfired when hot at low rpm, I drove it for a year before it was discovered.

[TimJM]

purpleliability said:

Has anyone got a picture to hand of it the right way round so I can check please? Thank you!

There is a pic at the start of this thread:
http://www.pistonheads.com/gassing/topic.asp?t=818...

But, the RV8 one looks identical but is only 2.5bar. If you have had this replaced recently make sure some numpty hasn't put an RV8 one on by mistake. That's what happened to mine.

[purpleliability]

Thanks chaps.

The FPR is the original one and plumbed in as shown on the picture.

With the injectors, i assume that the injector number is the same as the spark plug number right? Ie spark plug 1 is injector 1 etc?

[DuncanM]

Any progress with this Barry? I have literally the exact same fault and whilst it went away for a while, it returned when I ran the car low on fuel.

Which suggests to me it is fuel related somehow despite new fuel pump and filter.

Please let me know if/when you find a resolution .

Duncan

[purpleliability]

More double checking of everything today, coil packs register 1.5V at the connectors when the ignition is set to "on" (but not running), does this sound right?

All the HT leads, injector loom etc are on the correct cylinders, the injector loom all measure at 2.8v when idling, I'm running out of things to test now!

The misfire is still present on load but it runs very smoothly on light throttle openings, all the way through the rev range.

Arrrrggghhh!!!

[PoleDriver]

It really does sound like fuelling!