Overboost problem

[Darrell Jackson]

I have a problem now that at WOT I get an overboost condition and it will also cause the car to detonate a little. For the overboost, I checked the waste gate actuator off the car and it appears to be working fine. I'm not sure as to what pressure is supposed to actuate the arm, though. The GM manual says a .015" movement with 13-14 lbs. of pressure, which would be hard to see, so I hooked a compressor to it and it actuated each time I hit it. The waste gate itself is working fine. The car started doing this after Thanksgiving in which we had a few cold days here in NC. Before that it ran really well. Yesterday I ran it a few miles, bought it back home, gave the gas in park and it let out some small backfires when giving the throttle a few blasts. This would seem to maybe a MAF problem or an air/fuel ratio problem. Checked the fuel pressure and was within the specs---- my car is all stock, except for a 160 degree T/stat. My biggest question if there is problem with this sensor or another can it ultimately cause an overboost problem? I have also looked at the hoses for the wastegate and solenoid to make sure they are still good-- 6 months old--- looked fine. Also the hoses for the intercooler look fine.

Darrell Jackson
'87 Stock GN

 

[strikeeagle]

If you still have the stock wastegate hole in the turbine cover, it could be the culprit. That's where boost is bled off, and if the hole is too small to handle the additional air the motor is moving in this cold weather - voila!!!

To underscore my point about how small these holes are for even stock TRs, the turbo that Garrett supplied Pontiac for the TTA had a larger hole...

 

[UNGN]

If the hoses are new, you could have gotten one with a small orifice. The orifice (inside the plastic "Y") should measure .050".

Some of the defective ones measure less than .030". This will lead to an overboost condition almost every time. If you have the original "Y", put it in with the new hoses and see if that helps.

 

[Darrell Jackson]

Thanks for the replies. The hoses are the same as the older ones I had on the car and the rest of the parts haven't been changed or modified. That's why I'm scratching my head over this. This is the first time this car has ever reacted like this to cold weather. I've had it for almost 3 years now and my brother was the original owner and I talked to him and he said it never had this problem either.

 

[strikeeagle]

What are your before and after boost levels?

Is the puck binding in the turbo elbow? Unhook the actuator and make sure the swing arm moves freely through its full stroke...

 

[Darrell Jackson]

Before I was getting 13-14 lbs. of boost with the stock set up, now it will go to around 19 before I let off and the motor doesn't like it at all--- will get some knock. I let off quick-- don't want to blowa head gasket. The waste gate puck moves freely and that's why all of this is confusing me. I spent the last couple of days testing most of this stuff and it all appears to be working right. Thanks .

Darrell Jackson

 

[strikeeagle]

Solenoid?

 

[Darrell Jackson]

Thanks for the replies,

I did plug the small hose connected to the solenoid, where only the actuator would be in the circuit and took the car out and yes the boost worked properly. Reconnected the hose and the same overboost, so the problem appeared to be the solenoid. I then got the '87 GM manual and even though I haven't gotten any codes I did T/S code 31 (waste gate solenoid). The first step with ignition on disconnect the solenoid and connect test lamp to see if it's on/off. If on check Circuit 928 to ground ( wiring from the solenoid to connector D pin3 on the ECM). Did not have a test lamp, so I checked for voltage across the pins A and B to the solenoid and found I did have 12VDC, which according to this test, with ignition on, I should not have the ground signal from the ECM. I then isolated the ECM from the wiring harness (unplugged) and measured resistance from pin B (circuit 928)of the solenoid to GND. and had 7 OHMS, so this appears to be the problem. 7 ohms is not a direct short, but it is close enough to gnd potential to cause 12VDC to be felt across the coil of the solenoid, so it appears with this happening the solenoid is open all the time causing the overboost. So, guess when the weather and time permits, I'll have to check out the wiring and see if it is pinched somewhere and repair and retry everything again. Hopefully the ECM is not hurt at this connection D3 and is always applying a ground now or that would have to be replaced. The coil on the solenoid has a resistance of 33 OHMs well within spec according to GM's not lower than 20 OHM requirement. It also said ti check the purge canister solenoid which was also good. Thanks,

Darrell Jackson

 

[V8KILLR]

I agree with UNGN. Take off the plastic "Y" and drill it out!!!! Even the stock Y from GM can be too small. What do you have to loss, takes 5 mins if that to drill it out. And I think it will solve your problem. Please let me know if it works.

Jason

 

[Darrell Jackson]

I put the original "Y" connector back on before I plugged the hose at the solenoid and still the same problem, that's when I went through all the other checks.

Darrell Jackson

 

[Darrell Jackson]

I'm finally back---- lost a few days due to power outages here in NC because of the ice storm. I want to thank you all for the replies--- I did try every suggestion. What I found is that when I did fix the wiring issue I still had the problem, so I unplugged the solenoid from the connector and ran the car for a couple of miles, hit passing gear and the boost acted properly (13-14 Lbs), and the computer flashed the 31 code, so the ECM looks good. Cleared the code, then as before plugged the electrical connector back up to the solenoid, then plugged up the vacuum hose that goes to the solenoid and it showed once again 13-14 Lbs of boost. Then got it home and hooked up a vacuum pump to the solenoid and gave it 10 psi and it did leak down slowly, so I'm pretty sure a new solenoid will fix this problem. I wanted to thank you all for all the replies I received. Thanks once again.

Darrell Jackson
'87 Stock GN

 

[strikeeagle]

 

[V8KILLR]

Good work Darrell!!!! I admire that you have the willpower to keep a GN stock, I just couldn’t stop moding, love the speed.

Jason

 

[Darrell Jackson]

Yeah, I remember this one I have when it only had 15 miles on it and my brother got it new it off the lot in Laurinburg, NC in '87. He used to whip the MC SS I had and also my big block (454) '69 El Camino (had no traction at all when lining up at a dead stop). So, I told him if he ever decided to sale it, let me know. About 3 years ago he decided to let it go---- it did need a new powermaster and bumper fillers and original GM paint--- so I got it and it had never been modded so I've decided to keep it that way. It still needs the paint ( very glossy, but has some stress cracks), but the car is still strong and most people in this area knows of the Turbo Regals, so I don't have very many people coming up beside wanting to play.

Darrell Jackson