F1nd3r05

Hey guys, I took my car out today and I am having boost issues. its breaking up in the upper rpms 5k+ and it just stops at 10psi. If i bring my foot up gradually off the accelerator but still climb through the rpms it pulls through. I have an 88 with a m44/51 motor with forged internals, lindsey super 75, lindsey chips to match, afm, k@n filter/adapter for afm, msd 2 blaster coil, ngk bpr6es plugs (pretty sure thats it), 65lb injectors, and an in cabin manual boost controller made by a company called atomic (borrowed from friends subaru). I tried clamping the line to the mbc and got the same results as explained above. I checked my spark plugs which are gapped to .025 seemed slightly white, besides of this issue the car is running perfectly. PLEASE HELP!

jmj951

Are AFR's normal? Do you have a wideband oxygen sensor? Does the turbo seem to be okay, spinning freely?

If nothing changed, you have no exhaust leaks, and AFR's are normal, then I think you're leaking air somewhere or your wastegate isn't holding. I would look at really simple issues such as:
1) Possible bad diaphragm on bypass valve (do you have another to swap out?)
2) Other possible sources of leaking air. Pressurize the intake system with 14 psi and look for leaks.
3) How old is your wastegate? Any chance the spring has gotten so weak it can't hold boost? Perform the wastegate test here to see if it's opening too early:
http://www.clarks-garage.com/shop-manual/exh-02.htm
You've already done the first step, Low Boost Pressure Test.

F1nd3r05

I just tried pressurizing at 14psi no differnece/no leaks detected. I will try to find my old diverter somewhere to see if it makes a difference. I have a turboxs blow off valve from my friends Evolution 8 that i can hook up as well to see if that is where the problem lies. my wastegate is original. I took the manual boost controller out and used a fitting to connect the charge pipe straight to the wastegate (this was a couple days ago) and it would only go to 5lbs. is that normal without having either a mbc or cycling valve? I will do the wastegate test as soon as i get a chance as well. Thank you for such a quick response!

F1nd3r05

I just tried the wastegate test and from cold to warm the pipe leaving the wastegate going into the exhasut never got warm. Also, I was messing around touching everything and i realized the harness that goes to the injector closest to the firewall had an issue. When i touched it just before the injector the car would die. I opened the rubber part by the connector and saw that the rubber around the two wires was gone and they could have been touching but i guess werent. Could that being open have caused fuel to cut out at high rpms? I seperated the wires and put electrical tape around each one and then plugged it back in and the car starts up fine. Now when i try moving around the harness nothing happens at all. Im not an electrician, but does anyone think that (i dont know if this sounds close to right or correct or who knows what) electricty could have jumped or gone between the two wires under load causing fuel to cut out? Please let me know!

F1nd3r05

In regards to the post above. When i say i can move the harness around nothing happens I MEAN that the car runs perfectly and there is no stumble or stall.

mahoney944

I would bet on a wastegate issue, a stock wastegate with a super 75, most stock wastegates are failling at this time in their life let alone with a turbo like that. If you really want to test it and be positive and confident in the wastegate, pull off the wastegate dump pipe so you can watch the valve open on the bottom of the wastegate and run about 15psi from a shop line to it and while the pressure is engauged use a shutoff valve to lock the pressure inside the wastegate. The shutoff valve needs to be between the shop line and the wastegate. The valve should stay open as long as the shutoff valve is closed, once you loosen the shutoff valve it should spring shut and you should hear the pressure release. If you close the shutoff valve and the wastegate slowly closes while the pressure is locked in then its a bad wastegate. The warm/ cold test on a wastgate only tells you if the wastegate is seized in a stuck position, where the valve isnt fully shut even at idle allowing the pipe to get warm. The test above will tell you the condition of the diaphram. If the wastegate checks out then check the vac lines as one maybe be leaking or exhaust leaks.

jmj951

According to Clark's Garage (per the link I posted above), the wastegate should start opening at 4psi, so if it won't hold more than 5 psi, that seems normal.

Clark's Garage:
At a pressure of approximately 4 psi (0.2 bar), the wastegate should start to open as indicated by a temperature increase in the wastegate bypass line.

F1nd3r05

Does the vacuum increasing after i tap the throttle at idol mean anything to you guys? CHECK IT OUT ESPECIALLY AFTER THE LAST REV! It goes from 15-16in/hg up to 18-19in/hg!!!!

mahoney944

mine never goes below the 18 - 19 range, though mine has lots of mods. I would check for a vac leak.