LET misfire ongoing problem

[garethcolley]

Misfire getting worse the hotter the engine gets. Sometimes cuts out, once left for 20 minutes you can sometimes drive off again with no misfire until it gets really hot again. Best way i can describe.

Replaced:

Coil
Leads
Dizzy
Rotor Arm
Plugs
Fuel Filter
Injectors
Head (Previous one had cracked)
CTS
Idle Valve
Intake air sensor


Rolling roaded perfect then as soon as i got back it started. Phase 1 superchips with Walboro pump standard fuel pressure with standard injectors. Now standard GM plugs. Had previous misfire problems with Saab red injectors, swapped for rolling road and made perfect power. Any ideas as its at a stage where im close to getting rid. Had on going issues for 6 months.

[The Simps]

Have you tired running without the chip fitted and also a different ecu?

[meritlover]

are the plugs the correct heat range?

what do you mean 'really hot' surely if the cooling system is working correctly it should be cold or normal operating temp?

does it happen under load, high RPM over-run, idle....?

[belly257]

what fuel pump you running? is it in good order?

[garethcolley]

Thanks for replies....plugs are now standard GM which ive been told by Superchips is what this chip was mapped with. It doesnt follow that much of a pattern really...recently when i first start it up its fine. Then i thrash it around afters its warmed up. As soon as i start pulling up at traffic lights and pottering around it hates it and starts missing. It then tries to cut out sometimes between gear changes or when the clutch is dis engaged.

Update: Last night due to me doing minimum mileage i took the battery off to charge. Put it back on and drove around the block a few times and it was perfect. Could this have any effect if it was flat or maybe it could just be that i reset the ECU?

Simps: Ive tried a different ECU yes and still did it slightly. Dont have standard chips so might just buy a Phase 1 EDS opposed to Phase 1 superchips that ive got now.

With regard to loads etc....it varies. It really does seem to be the more gently you drive it the worse it becomes. It doesnt misfire as such at full boost as once its started misfiring it does it through the full rev range ie, not just at say 1-3k.

Really out of ideas now as there isnt anything to replace.....as for fuel pump its a Walboro but not sure which. As for condition im not sure...rolling road session showed good fuel 'see my projects the pics are on there) delivery.

[Ben]

Possibly a bad earth and removing refitting the battery you might have cured it.

[garethcolley]

I checked all earths, they are all fine. I did think that was the problem initially.

[craig green]

Make an earth lead from the alternator to the -ve battery terminal. See if that helps.

IS the CTS wiring intact where the wires are exposed?

Checked for any inlet leaks under the top hat? (spray carb/brake cleaner whilst eng is running)