Previa Mis-Fire

[leftfieldphoenix]

Hi everybody,

I am a new previa owner having come back to the marque after an absence of some years. I have a 2001 2.4 petrol previa with an lpg conversion. it's done 83000 miles which appears to be genuine from the mot history and general condition. I have a mis-fire which I am struggling to diagnose. there are no warning lights on the dash and there are no cooling issues to suspect head gasket.

The symptoms are that the mis-fire is present whether running on petrol or lpg. the vehicle struggles to idle until thoroughly warm and there is a constant mis-fire throughout the rev range. the vehicle will stall if left to idle for any length of time and top acceleration and top speed are severely limited. fuel consumption is horrendously bad.

I bought the car with the mis-fire having read about the range of issues that can cause a mis-fire in this engine and have gradually worked my way through the following by physical inspection: throttle body and egr have been thoroughly cleaned, ventilation valve cleaned, MAF sensor cleaned, purge valve tested, plugs and coils changed. the two pre-cat lambda sensors have been changed.

I have tried to see if there is a fault on the coil loom by disconnecting the coils in turn. the vehicle will start on three and seems to run identically regardless of which coil is disconnected.

I am going to have the vehicle diagnosed but it can be difficult to find a tester with the right scanner to produce reliable results.

So, I am looking for a few things if possible:

1) suggestions as to what is left to check?

2) if I have a diagnostic done, what scanner would be best used?

3) can anybody recommend a good diagnostics chap local to me in Leicester?

Any help much appreciated.

[leftfieldphoenix]

Since my last post i have had the vehicle scanned and compression tested. compression is good and even across the cylinders. the diagnostics show that there is a coil fault across all four coils intermittently, both as a stored fault and newly generated whilst running. This is the cause of the mis-fire, but given that the coils have been replaced once and that all four are malfunctioning I am wondering if this means that there is an ecu fault or a fault in the wiring loom. does anybody have any other ideas, or ideally has this problem cropped up before?

[Devon Aygo]

A long while back there was a Service campaign ( not a recall ) on 2.4 Petrol Previa relating to heat damage to the wiring harness for the coil packs, if damaged the car could suffer from miss fires and or EML lamp on. PM your chassis and I'll look to see if this applied to your car. What where the fault codes stored when the ECU was read?

[leftfieldphoenix]

so here's the latest. I have found that two of the pencil coils are loose because the threads in the rocker cover have been stripped. The threads in the remaining two are partially stripped so I have decided to replace the fixings by drilling through and glueing threaded studs from inside the rocker cover to leave a protruding stud which I can use to locate the coils. Although the coils being loose is obviously not ideal they were nevertheless still quite secure so I am not convinced that this is the root cause of the problem. However, we shall see.