Failed MAF or Turbo??

[silviadad]

My sons car.
S14 swap in a 92 Hatch. Engine was rebuilt last year, .020 over stock compression everything else is stock except FMIC. Engine has run great up till now.

He was driving it and had it under boost in 3rd gear about 6500 rpm, shifted to 4th and it fell on its face and wouldn't make boost. Engine is running rough, bucks and chugs at lower RPM's and will only make about 5lb boost when we do get it wound out in 3rd but it is very slow to get there. At idle it surges (hunts) between 700-1000 rpm. Vacuum is 16 to 18 depending what the idle is doing.

What we have checked.

I suspected a blown coupling. We checked them all and they are fine.
Did a smoke test for a vacuum leak and all is good.
Pulled the plugs and they are fine.
Compression test on the engine cold was 130-135 on all four. That seems a little low but I thought it may be the cold engine.
Replaced fuel filter, I did not check fuel pressure though.
Cleaned the MAF.

I had him pull the hot side piping off and there is oil in the piping, not a lot but it is there. The turbo still spins free and does not have any excessive end play or run out. So I do know the turbo needs a rebuild kit and we will be doing that soon.

So now here is where I'm getting confused, when I unplug the MAF at idle the engine will sometimes continue to idle and other times it will die out in 10-15 seconds. It always dies if I plug the MAF back in.

The other item that has me puzzled is if I unplug the O2 sensor nothing changes. The check engine light does not come on, we checked the ECU for codes with the write up that is posted here. No codes, LED does not flash at all.

I have a wide band O2 sensor in my race car and can pull it out and hook it up in the 240 but it would be a big PITA at this time. If someone thinks we need to do it I will.

Any suggestions? Thank you.

Lee

[RalliartRsX]

1) Did you physically remove the couplers to check for leaks?? When I had a similar issue, the couplers all looked fine until i removed them and one (the turbo outlet) had a tear. It would only open under pressure so upon initial inspection, I didn't see a thing. It was not until I removed it and "squeezed" it until I realized the issue

2) Also, did you check the wastegate arm/diaphragm to make sure they are in working order??

3) Unplugging the MAF while idling, the engine should sputter out as the ecu will revert to running rich.

4) Did you check to make sure the turbine wheel is also all intact??

5) You NEED w wideband on that thing

[wolfpack]

I would give the 'manifold-to-turbo' gasket a look... The nuts tend to back off, and then you blast a hole through the gasket. Ask me how I know...

By the way, it's awesome you're on here looking for advice to help your son out! My father got into my Nissan with me and we have a blast together!

[silviadad]

He pulled all the couplers except the ones on the intercooler and those were fine. I want to check the IC and those couplers next. They look ok and the clamps are tight but I know they need to come off to be inspected properly. That is tomorrows project because the bumper needs to come off to do it.We checked the waste gate and it is functioning correctly.We didn't pull the down pipe off and inspect the turbine side yet.If we don't find anything wrong with the IC and couplers that will be next.I know it needs a wide band but it is going to be up to him to buy one. I run an Innovate MTX-L in my blown race car and it is an invaluable tool for tuning.The manifold to turbo gasket is good and there are no exhaust leaks.It almost has to be a vacuum/boost leak or a restriction and since it went south under boost that would lead me to believe that even more but we sure can't find the culprit....hopefully the IC couplers are it.Thanks for the responses.Lee

[silviadad]

Jesus I don't know what happened to the spacing on that last post, tried to fix it but it keeps staying the same. Sorry

[fliprayzin240sx]

Did you pressurize your IC pipes to check for tears? I still think you have a leak. Make a cheap boost leak tester with 3" PVC pipe cap, drill a hole thru it, put wheel air valve on it, plug it into intake neck where the MAF would normally plug in...pressurize it with an adjustable air compressor and slowly raise the pressure up to about 15 psi.

[ultimateirving]

Yes symptoms coinside with boost leak. So build a tester and get to it because turbo.

[silviadad]

Boost leak. Hot side coupler on IC is torn. Ordered all new couplers.Thanks guys!

[silviadad]

Well that wasn't it. Idled better when cold but when it warmed up the hunting came back and it still didn't want to boost or go above 5K.

Spent the last couple days checking for more vacuum leaks, checked TPS voltage, ignition timing, IAC , fuel pressure and everything else I could think of and didn't find anything. I started unplugging the injectors one by one with the engine idling, #2 didn't change a thing.

We had done a compression test and that was good and the plugs looked fine.......BUT I didn't look closely at the coil packs!!!!

These little engines just amaze the hell out of me that they will run fairly well on 3 cylinders!

Here is number 2.

Now we need to find a coil pack ASAP.

[cotbu]

I probably would have missed that too, but it looks like someone tried to repair it before. What does the top look like?
I have a spare set of coil packs, and I'm willing to help you out.