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Intermittent Misfire ?

Frenchy

Frenchy

Active member
Member
Gents,
Took the 88 Turbo out for a run today, stuck some 97 BP in and went for a tootle about, let her get warmed through then started to hit low boost levels 3-4 psi through the gears, then a big back fire and a hesitance when accelerating, eased off and everything back to normal ?

This has happened 3 times now since i had the turbo side off including turbo whilst fitting a boss for the AFR lambda probe, got home and changed the plugs from Bosch Super 4 Iridiums to the standard Bosch super 4's checked all air hose connections for tightness, main plug lead cleaned and refitted with copper grease on the contacts.

As said this has happened a few times now, then the car is perfect ?

Running chips, 3 bar FPR, Tial wastegate, Bailey DV,

Any ideas ?
 
Have u changed the fuel filter at all ? When was the last time the fuel pump was changed or upgraded ?

Is the misfire across the whole rev range or just at wot on full boost ? If the later can often be a fuel issue.

Chris
 
Is there a lot of smoke. Sounds like you may be overfueling on boost. This has happened to mine and it was caused by a small crack in one of the boost hoses which was leading to a loss of boost pressure and subsequent overfuelling. It took me a while to work this out as I checked pipes a few times.

Sounds stupid but did u connect the vaccuum pipe back up to fuel pressure reg (also is the vac pipe plumbed in right so that its engine side of throttle body so that you get negative pressure when trhottle is closed)? Check that you have vac pressure at fpr and that there are no loose / missing vacuum hoses.
 
Cheers Chris/u63, the fuel filter is recent but still has the original pump, car was only on part throttle not WOT, the hose theory is worth following up as most of them were off whilst removing the turbo and downpipes ??
 
UPDATE...............Took the car out again today after reverting back to original plugs (Bosch Super 4's) and when warmed up and hitting boost seems to be behaving now, the only other change was a strip down and lube / re assembly of the Bailey dump valve, and the main HT lead cleaned and re seated, hopefully sorted now !
Time will tell.
 
James,
My guess was going to be the injector operation was sticky, at least one was sticking open, causing over fuelling.
There was a fuel build up (egg cup full) in the silencer and high boost heat ignited it??
Hesitance caused by the impeller being stalled by the pressure of the bang when the fuel ignited
George
944t
 
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