4g94 Flat Spot

S

sammyg

New Member
Hey Guys,

New to the forum here. Just looking to get a second opinion here.

I'm 16 and just completed a 4g94 engine swap into a 1998 CE Mirage. I rebuilt the engine with CP Carillo high compression pistons (11.5:1) and K1 connection rods. Currently running SOHC head with stock cams. I got the engine in and is now running smoothly (thanks to LLT racing for the reflash), but it does have this problem which Im having trouble figuring out.

Between pretty much idle and 3,000rpm it has a major flat spot. A flat spot as in it seems to bog down, not make much power and very slowly increase in RPM. What I have figured out is this only occurs in 2nd gear or higher (something to do with load being on the engine??). It also only occurs when you put the throttle past 50%. Anything before that and the engine runs fine, its just after that 50% throttle that it bogs down. When i was getting tuned we could see that when the engine 'bogs down' it is running very rich. It goes from around 13.9:1 to 9.8:1. Once it reaches 3k RPM you can floor it and it takes off without any worries at all.

In my attempt so far I have changed the manifold and throttle body to the 4g93. Im running 4g93 MAF and TPS. 4G94 injectors, 4g93 ECU. Exhaust is stock however the cat has been punched out and muffler replaced with a high flow muffler. Not really sure what else would be causing this. Any ideas or theories would be much appreciated :D

Cheers,
Sam
 
With my limited knowledge I assume it may be running a bit too rich therefore that's why it's bogging down so as Tron said take it back to LLT and get it reflashed
 
When I got it tuned the first time, he said that there was something influencing the engine causing it to run rich or cause it to bog down. Because I built the engine, he said to go back and check everything like plug gaps, timing and all that. Just about everything seems to be up to scratch.
 
if that the case my guess is maybe the MAF or o2 sensor is playing up (just a guess so could be something completely different)
 
Crumble said:
if that the case my guess is maybe the MAF or o2 sensor is playing up (just a guess so could be something completely different)
Click to expand...

Thats what Im probably leaning to. Ill check the resistance and voltage through it tomorrow. It had been sitting up in the attic for a while and it looks like some of the 'honeycomb' fins are bent out of shape (causing it to get the wrong reading).

Apparently when he did the tune he deleted the 02 sensor. Now it is just acting as a plug for the headers
 
So did you go back and check everything?

Are you running different injectors or MAF or anything,
 
Trondabron said:
So did you go back and check everything?

Are you running different injectors or MAF or anything,
Click to expand...

I've checked just about everything, only thing I haven't paid attention to was the valve clearances. They haven't been checked yet. Would this cause something like that? The fuel filter is also due for a change however Im pretty sure its not the cause as the car is running rich when this happens.

Im running the 2l injectors on the 4g94, the different manifold seemed to help the throttle response a little bit. Actually now that I think about it, the TPS hasn't been adjusted yet. When it was running in my old MR the motor ran fine. It hasn't been touched since so I would assume that it is out.
 
geezus... 16 and already outbuilding 80% of the forum, when i was 16 i was still learning how connector-pens could be made into rubberband guns..

all serious though if you know how do do what you have done so far you should have the knowledge to troubleshoot your own build

asside from tune, fuel filter and 02 sensor would be a good idea to check, basically anything that could effect how much fuel you are getting so if ur running maf then check that too
 
I'm going to swap out the maf and TPS tonight for reconditioned ones.
I'm pretty sure this is the problem, it's what I've narrowed it down to

I'll let you know how it goes
 
So after replacing the TPS and MAF the problem seems to be fixed!
Although everything seemed to be fine when checking them, something must not of been working correctly
 
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