Overboost ?

[grondie]

Hi everyone,

I'm having an issue with my 85 that has a rebuilt turbo with about 2k miles on it. The car doesn't seem to be limiting the boost, and the dash gauge goes into the red under heavy acceleration. No over-boost buzzer goes off either. I checked the wastegate connector that likes to fall off, and it's connected and the bcs is also connected. Is there a way to check the wastegate? The repair manual pretty much says "replace turbo assembly ".

Thanks!
Bob

PS: The car is stock

[pacwest]

Replacing a wastegate is easy. Not like changing a light bulb but it's done in under an hour.

Most likely your overboost buzzer circuit just doesn't work. Does it misfire and run rough after you get on it? You are browing out the plugs if so. Overheating them.

I say replace the wastegate and then diagnose the overboost buzzer. Not a tough one.

Just take it easy, don't blow it up.

[merkurdriver]

You can check the functionality of the wastegate actuator by using a beachball/basketball pump. Just put the nozzle in the line that goes directly to the WGA and apply pressure. The rod should move and hold pressure - if it doesn't then the WGA is bad resulting in your overboost condition.

[pacwest]

Make sure you have absolutely eliminated a hose coming off as the culprit.

9 times out of 10 a Merkur fix is a simple one. Design flaw (fixable) or the previous owner kludging it.

[93supercoupe]

what is stock wastegate spring pressure? i thought it was 10 but my accurate dash gauge(lol) says 5.

[merkurdriver]

what is stock wastegate spring pressure? i thought it was 10 but my accurate dash gauge(lol) says 5.

Its 10psi.

Stock boost gauge has been known to lie.

....or you could have something restricting your boost to 5psi.

[John R. Rowlands]

grondie,

Nope! I think you have a bad boost control solenoid. Is it the original or do you have an aftermarket? Is the 12volt plugged it?

John

[grondie]

Hi everyone,

Thank you very much for all the help.

pac: I checked the vac hose going to the wga, it's tight and looks like it was replaced when the turbo was rebuilt.

john: I swapped the bcs with a known good unit from my 88. Still runs the same.

merkdriver: This is next on my to-do list - thanks! If I could only find my old air pump! Also, yes, I don't trust the gauge. But, under hard acceleration, it started knocking/pinging - not good. So, basically, I've been going easy on it until I can check the wga with ye olde air pump.

[xrattiracer]

so the hose is good, great. did you actually test the operation of the wastegate? or at least tried to blow into it (shouldnt be able to)?
if the bcs is in question, just bypass it by connection the two hoses together. hell, just do it anyway, it serves no usefull purpose.

[Ray]

so the hose is good, great. did you actually test the operation of the wastegate? or at least tried to blow into it (shouldnt be able to)?
if the bcs is in question, just bypass it by connection the two hoses together. hell, just do it anyway, it serves no usefull purpose.

on a stock car with no aftermarket boost controller, it increases boost in all gears but 1st iirc to 14-15psi

[xrattiracer]

actually it just limits boost to 10 psi at lower rpms. the ecu in these cars has no way to know what gear the transmission is in, so what youre saying isnt possible. by bypassing the bcs it just stays at high boost (15 psi) all the time.

[ginandtonic]

My 88 is overboosting as well. BCS is bypassed, Turbo outlet hose straight to WGA. My guess is the actuator since it took nearly 90 psi from my compressor to activate it. If everyone agrees, where can I find another actuator?

[boostedxr89]

word of wisdom-- dont throw away any spare parts cause someone will need them.

[grondie]

A quick update on this issue. I did check the wastegate with a pump and while it did move, it only moved about 1/2 inch. A quick call to MPM, another wastegate showed up (thanks jeff!) - 2 hours later it's working like a champ.

Thanks to everyone for all the help!