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C20LET Rev / missfire issue

1K views 20 replies 6 participants last post by  Mark_F 
#1 · (Edited)
I've been having a problem with my GTE.

First and second gear, its fine. Into third and when you are full throttle, it gets to about 5k revs then the rev counter drops off the digidash (but the car continues to rev) until it violently hessitates. - Before the limiter. :confused:

The rev counter dropping off made me check and change the crank sensor. Problem remains.

Interestingly, if you are 1/2 (roughtly) throttle or less, it pulls to the limiter. Occaisionally, it will pull to the limit on full throttle, but this is rare.

Plugs are standard GM, gapped to .6mm

The fuel reg is a 3 bar job I think, this will be changed soon.

No Fault Codes

Any ideas?
 
#2 ·
i'd be checking your fuel pump relay. This has 2 smaller relays in one unit, one switches on the ECU, one does the pump. If the pump draws alot of current, and the connections inside the relay are flaky, this could cause the pump to switch on/off, causing violent hesitation, or the ECU could be switching on/off causing violent hesitation.
I had this problem, and my rev counter would walk about when no change in engine revs lmao
strange though, as the rev counter receives the signal from the ignition amp via the green wire, and this is not related to the ecu:confused:
anyhow, check the relay, swap it for a known working one if you can:nod:
 
#8 ·
well, the 'fuel pump relay' is what people use referring to the small black box, which actually has 2 relays inside, 1 fuel pump , 1 ECU. The 2 relays share some pins, and tracks on the board, so if it's really naffed, can cause your ECU to drop off too, short + and - and all sorts of stuf !
 
#7 ·
ACT = Air charge temperature.

I'm not 100% sure which way the overboost system works but if it cuts ignition then that would explain the loss of rpm reading. Its probably worth turning the boost down a re-testing just to be sure. Make not of the settings before hand should you need to revert back....hope you have a boost guage.
 
#9 ·
Having replaced the relay, problem remains.

I'm now thinking:

Leads - Pretty new
Plugs - GM, gapped to .6mm, again, relatively new
Rotor - Again, pretty new
AFM - ? Could be?
K&N filter - Sucking in hot air maybe?

Still don't understand it pulling to the limiter if you pass 4k at half throttle. Once past 4k, plank your foot and it pulls all the way to the pop pop pop rev limit.

If it were overfuelling, could this cause that problem?
 
#11 ·
Replaced the battery earth, gearbox one seems fine, injector ones also, what other ones are there?

Don't see the Intake temp being too high, running low boost with fully exposed EvoVI cooler and outside temps being around 0°C..

Going to drop the boost a couple of PSI and see if it makes a difference.
 
#16 · (Edited)
:(

on the XE/LET, the ECU is earthed on the fuel rail iirc, as opposed to other cars that have a chassis earth for the ecu.
if you really want to know these, you could find the 'engine' end of the wires (on a plug somewhere), poke one multimeter probe in there, then try each pin on the ECU plug with the other end, when contact made look up the pin on the pinout knocking around on migweb somewhere :beer:
 
#19 ·
I really don't see how it could be the gearbox at fault. Its done 10k miles max since a rebuild, it isn't on its way anywhere. As for fuel pump, it could be, yeah. Only running @ 2.5 bar just now so I don't imagine it having too much trouble.

Will do the fuel filter next. I have another ECU with EDS chips sitting and an Apexi, this may be the next port of call..
 
#21 ·
Interestingly, after losing it with it, leaving it standing in the garage for a week, I went back, put the boost up a couple of pounds and went a drive. It now feels, sounds and acts better. It rarely hessitates now.

Was it maybe over-fueling before? I know its not set up right to be running standard boost just now, it was mainly aimed at when it goes Phase 3.5
 
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