Ok, so I am finishing up my build (T2 swap) into my 91 coupe.. Everything went awesome until....

Car has been running and driving fine, starting right up and idling at about 900.

I took it for a little test drive today (to burn off some MMO in the exhaust) took it easy on it and was just letting her get use to being on the road again. I got it up to temperature and then rolled on the throttle a little, it got into boost just a little. When I put the clutch in to stop at the end of my road it died on me.. Started right back up but I had to feather the gas to keep an idle going. under 2krpm the engine was unstable and shaking around a little (not super violent but didnt make me feel good)... The car ran fine above 2krpm and I drove it right home. It still starts right up although will not hold an idle.

I checked compression all is well super strong puffs on both rotors.

I have a few theories and would like your input.

1) I blew a vacuum cap/ or clamp off the intake somewhere (looked and saw nothing)
2) The stock FPR can't handle the warbro 255 (but why did this become an issue under boost)
3) My plugs are fouled from the MMO treatment
4) Bad AFM?? (but also odd that it was fine until the first time the car saw boost)
5) bad or insufficient ground on coil
6) open atmosphere BOV stuck open after venting?
7) low fuel?

The car as it sits consists of the list below:

1991 FC3S with 103k miles
Red w/ black interior in Mint condition
Tokico Blues with Eibach springs
3 inch full single exhaust downpipe to tailpipe
4 port t2 engine and transmission
stage 2 clutch
Racing beat T2- N/A rear shaft
Strutbar
Custom pillar gauge mount (molded in)
Upgraded BOV and charge pipe
2751 Engineering Emissions block offs
Blitz intake filter and custom short intake tubing
Walbro 255glph fuel pump
Some other parts I have forgotten..

Let me know your thoughts or experiences..

 

Vacuum leak...start checkin the intake,throttle body.hoses etc..(yay..fun)

 

+1 ,vac leak ,, if s5 check the plastic pipe that feeds from turbo to top mount for cracks
check also the connector on the AFM

 

I would almost put money on vacuum cap/line. Had this exact same thing happen to me. F-ing line was under the intake and I couldnt see it was off.

 

Off to hunting for vacuum leaks.

 

I am going through same issues, I made a pressure tester from Home Depot Racing. I got a pvc test cap for .30c and bought a shrader(?) valve from the auto parts store. Drilled the cap and pulled shrader valve into it. I got 3" coupler and hose clamps and put it in place of the air filter, clamped onto the air flow meter. I set compressor regulator to 10psi and pressurized the intake and found the leak with soapy water. Found vacuum leak or boost leak in a couple of seconds. Cheers.

 

The small hose going from the charge pipe to the IAC. Check it out, it's hard to see when it pops off. I had to hose-clamp mine.

 

Intake pressure tester visual aid. Works great.

 

Haha, that is exactly the same as the ghetto rig I made to find a coolant leak on my wrx. Worked awesome!

 

Found the leak.. Surprise surprise, it is my inexpensive BOV.. Inner seal folded over... back to the drawing board.

 

Well at least you found it. What kind of bov did you have that failed like that?

 

You get what you pay for... It was like $28 off ebay. I have reached out the the seller. Although I think I discovered the failure point and may have repaired it from occuring again.
Attached is a picture of the S-type BOV I procured from ebay. The only reason I went cheap was I could not locate a stock BOV/charge pipe so I had to improvise..

 

Yeah...ditch that thing in a hurry. Even the original that it's a copy of (greddy type-s) is junk. I've never seen one that didn't start to leak boost around 12psi.