4agze engine problem - hesitates under load...

[mookschank]

Hi, I asked this Q at twincam and thought you folks might be able to offer some advice with my problem.

My car has a newly rebuilt AFM DLI 4agze, shims clearances properly adjusted, correctly timed, about 500kms.
SC14 conversion, running about 10psi under light-med throttle.


Under medium to heavy throttle my engine usually has a hesitation, poor power sometimes (not a lot of sweet spots so far) and on occasion the car bucks, like a bull The car idles fine and revs fine under no load. I took a spark plug out the other day and saw the white marking leading me to believe lean burn.


To rectify the lean burn I have so far:-

1. Checked the fuel rail pressure at idle and load, and all is good and fuel psi raises under boost.
2. Taking cold injector off to fit gauge and the pressure was held in the fuel rail, so injectors holding pressure ok.
3. Changed AFM box to another known good one, no change to the above.
4. Changed TPS and reset properly, no change to the above.

Would lean burn cause my problem as above? And if so, what other things can I check to pinpoint the problem?

Please help, my surly car is pissing me off...!

[Cuzzo]

Stock ECU?

Id say TPS is out of alignment. You need to check it and compared to the specs in the gze manual.

[allencr]

What's the compression?


I think it's one of the below:

newly rebuilt
shims clearances properly adjusted - not that I think it's likely to be a cause, just that I've never read valve lash described that way
correctly timed
TPS... reset properly

[DX20VT]

Not the AFM getting to the limit of it's travel with the SC14 instead of the SC12 ??

[inertia]

Are you running bigger injectors? say the 440's from a 7mgte?

Had a friend in malaysia with the same problem, I believe upping the injectors fixed it, not sure though.

Can you get the duty cycle checked?

[Duk]

I reccon Cuzzo is on the money, either the TPS needs adjusting or it's Fcuked.
Stock injectors can still provide a 12.5:1 AFR on my twincharged 4AGZE, but I MAY be seeing that as a result of an ignition system not providing complete combustion .

Check for fault codes and AFRs if you have access to a wideband. Dud TPS use to show up as a bit of temporary leaness and a flatspot on my car years ago.

[mookschank]

Thanks for the replies.

Have already swapped out the TPS, put another in, checked with a multimeter as per GZE specs. However, it could be the TPS circuit perhaps?

Compression is std, 8.9:1 i think.

Yes, Std ECU. I also just got another one which I can try out. Just don't really want to swap heaps of stuff out, else my motor will be completely different ;-P

Ok, might look at the wideband route, will take it to a shop and check A/Fs. The thing is, there's not a lot to tune for A/Fs...? And I dont want to play with the AFM screw as the car was running ok prior to the rebuild (and prior to spinning a bearing).

I cant imagine sized injectors being the culprit if they are functioning ok. Std AFM should also not be a problem...

No fault codes, all good...(except for climate control!)

[Cuzzo]

Check the caps arent leaking inside the ecu also.

[mookschank]

Check the caps arent leaking inside the ecu also.

Not sure how to check caps, but I guess I can put in the other ECU to check...

[Duk]

Blocked fuel filter/dud pump?
If you can set up a fuel pressure gauge and take it for a quick fang while getting a mate to watch it, that would show up failing pump/blocked filter.

[Cuzzo]

Not sure how to check caps, but I guess I can put in the other ECU to check...

It would be a visual thing.

1jz ones:

[mookschank]

Blocked fuel filter/dud pump?
If you can set up a fuel pressure gauge and take it for a quick fang while getting a mate to watch it, that would show up failing pump/blocked filter.

Hooked up the fuel gauge to the cold start feed and squeezed it through the top of the bonnet and took it for a drive. Pressure was good, raised during boost, all within spec....I guess that rules out any fuel feed problems...

[mookschank]

Just popped the top off the spare ECU, these caps are smaller in real life Will do the ECU swap and see how it goes...

Here's my whitish spark plug...Am I reading the plug ok? Looking at internet plug pics is making me uncertain......Found this good site by the way: http://www.usaimports.co.uk/Mopar_Te...ug_Reading.htm

[mookschank]

Could a duff water temp sensor be a cause? If so, I can pull it out and boil it up and test....

[senn]

could be the ignition can't cope with the increased airflow of the new charger? (due to old plugs or leads or coil etc) i remember being told upping the boost can "blow spark out" and required stronger ignition etc...