Engine Issue - Possible Cause?

[davehart]

I have a bit of an issue with one of my GT's.

Its running a little bit rough, missfiring and cutting out. On idle the revs will slightly jump around and the little I've drove it it did the same, spluttered and tried to cut out.

I've done a few checks. TPS check, fine. MAP sensor checked, fine.

Engine Compresson tests:

Dry Test
105
105
105
105

Wet Test
120
120
125
125

Spark plug condition: Very black sooted up plugs.

It does have low compression pistons in but those readings are far to low and indicate a problem. Steady along all four so thats one positive but any ideas what internal issue I have before I strip the engine to bits?

 

[Jay]

So long as the basics are done (fault codes clear/timing set/ignition good/etc) you could look into more sinister potentials I guess.

Compressions look good and even so hopefully it's nothing bottom end.

Black sooted up plugs would point to a rich condition. Usually the plugs should be a lighter colour as it will spend a lot of time at idle and light cruise (lean conditions). If it were me I'd look into the fuelling before going too much further, a wideband would tell you a lot.

Beyond that when was the last time the valve clearances were checked? I had a similar rough running engine and it ended up being those. I'd had the head refurbished and so the clearances were too small. As a result some of the valves never entirely sealed shut causing crappy running. Knowing what a pain in the cock checking and setting clearances is I'd leave this till simpler stuff is checked.

Jay

 

[davehart]

The next thing to check is the timing. I've replaced all the ignition parts on it.

It does have an aftermarket HKS unit controlling the fuelling.

The lambda wiring looked a bit suspect so I've taken it out for now until I find a replacement plug...you got any around the workshop Jay? I'd prefer to keep the stock connector on the engine loom and find a spare plug to put on mine.

 

[Jay]

Unfortunately not mate.

What is the HKS unit and who has set it up?

Chances are it'll need a bit of tweaking..

 

[davehart]

Managed to get one, well, hopefully unless its another dodgy facebook sellar.

I'm not sure who mapped it, its an old Burwash build. I've spoke to a fair few mappers and none touch the HKS units these days. I'll be upgrading to a Link unit soon in any case.

I'll see if the replacement lambda makes any difference.

 

[Jay]

Is it a F-CON?

If so they are old skool units. The map is adjustable between 12 (going on memory here) settings using a small screwdriver. If it's not been setup with a wideband you could be running too rich or too lean which might have an effect on engine behaviour. If you were local I'd said call in and we'll get her set right!

 

[davehart]

Its a shame were a sea and a few miles apart Jay.

Yeah its an F-CON ProV Gold unit. I'm not sure who Burwash used to have these mapped back in the day but speaking to a lot of tuners they dont touch them these days and the software is impossible to find.

It's not got a wideband fitted, maybe another mod to do when I get the new ECU but with Link units you can pretty much have a data logger direct to your phone with the features they have.

New Lambda sensor arrived today with good wiring so thats one thing fixed and eliminated.