car has a major missfire problem it is becoming more often as soon as it warms up

 

changed two broken coil packs

changed plugs

checked leads

checked temp senders

done ecu test and had code 55

 

any other suggestions

 

could it possibly be air flow meter or head gasket failure!

 

turbos still boosting like they should

 

all advice greatly appreciated before i lose all interest in this heap of junk which has cost me 3500 in repairs etc so far

 

simon

1990 uk tt manual

have you had in on a consult? may throw up a reason, could very much be the AFM, also could be wiring, have you pulled off the plugs from each coilpack while its running and listen for it dying a little and plugging it back in and repeating over all 6? is it over heating or are you getting any water in the oil and vs versa? you can also do a leak down test to see if its losing pressure through the head gasket?

what speed you getting the missfire? normal crusing or on accelaration?

 

if it was the MAF the car wont rev over 2500 ish revs

 

If your getting code 55 then the electric system is ok as the ecu has a memory which will come up if there had been any fault even if the fault had cleard.

 

I think its prob some thing mechanical ie plugs or injector etc wont be head gasket

Is it after heavy rain by any chance??

 

Do you have a none standard induction?

couldnt this be the ptu porblem or wiring going to it

couldnt this be the ptu porblem or wiring going to it

 

 

thanks for the replies so far

i have another ptu which i am going to try rain does not affect it as it has totally standard induction.

 

is not using water and temp is steady

 

was thinking it was afm related as well but it is intermittant will probably have to buy or borrow another afm

did the ecu test which gave me the code 55... couldnt seem to get the o2 sensor test to flash anything up maybe i did not warm the car up long enough?

missfires whilst accelerating

 

any more suggestions most welcome

 

simon

thanks for the replies so far

i have another ptu which i am going to try rain does not affect it as it has totally standard induction.

 

is not using water and temp is steady

 

was thinking it was afm related as well but it is intermittant will probably have to buy or borrow another afm

did the ecu test which gave me the code 55... couldnt seem to get the o2 sensor test to flash anything up maybe i did not warm the car up long enough?

missfires whilst accelerating

 

any more suggestions most welcome

 

simon

 

It wont be the AFM or MAF (same thing) as i said before if the engine revs over 2500rpm, and you would have error code 12,its possible it could be the ptu, but then you could get code 21 for ignition circuit, but take the 2 connectors off each end and give them a good clean

Sounds like the PTU to me.

It very rarely shows the fault code but depends how it failed.

check the CAS plug also as this will also give the same kind of intermmitent fault.

In general, misfires that occur under load or in damp conditions are usually ignition related (Spark plugs, coil packs etc.)

Slight misfire at idle could indicate burned valve seats or fuelling issues and a slight misfire at steady revs (more of a flutter than a misfire) would indicate faulty EGR valve (not closing) but I don;t think 300ZXs have them?!

If your problem was caused by head gasket failure you would probably notice some of the other Head gasket problems first. (Lots of white smoke, using water, overheaating, heater not blowing hot, burning smell from engine, radiator boiling over when temp guage ok, water in the oil, oil in the water)

If you think either head gasket may be on its way out, rather than just a blow by test, get a block test done. This involves a small amount of carbon responsive liquid being held over your radiator while the beast is ticking over. If the liquid stays blue there are no problems but if there is any trace of combustion or oil in your cooling system the liquid turns yellow or green.

I wouldn't want to replace the cylinder heads without being 100% sure the gasket had blown.

If they are blown and you have to get the cylinder heads resurfaced, be very mindfull that you can't have much skimmed off them before the valves will hit the pistons!

thanks for all replies...

think i have found one of the faults

 

the connector to the ptu going from the right side looking from front of engine was loose as part of the locating plastic surround has or was broken so it was not seating onto connector properly i believe the last mechanic has forced this off with out working out how to

remove properly

 

will let you know how i get on

 

thanks

 

 

simon