Weird compression test - is this a BHG??

zyzx2k9 · 06-17-2011, 01:58 AM

I've got a 1990 Supra Turbo and was driving on the highway recently, and when I pulled off to park I could feel the car was running rough, really chugging. It was just a quick stop and when I restarted the car (still warm) a TON of smoke came out of the exhaust. It was at night so I couldn't tell if it was white or blue, but it definitely wasn't black. It continued running rough on the short drive home, but notably improved whenever I got the RPMs over about 2200. Smoke was pouring out the tailpipe the whole time, and particularly at lower RPMs.

From all I have read in the forums here, it sounds a lot like a BHG. So I took the car in for a compression test and the readings came out odd--all the cylinders had normal compression readings in the 160s, but cylinder #5 was off the charts at over 200. It was tested twice and came out the same both times.

Is this consistent with a BHG, or is there anything else that might cause these symptoms? I'm almost ready to take the plunge and replace the head gasket, but I'm holding out hope there might be something more minor that will resolve the problem. Thanks Supra community for your insights...

El Supracabras · 06-18-2011, 12:19 PM

The only thing I can think of that will increase compression is if something (carbon deposits, oil,coolant,fuel) is taking up space in the combustion chamber causing the air to be compressed into a smaller space. If there was coolant in the cylinder from a bad head gasket it could increase the pressure. Is the coolant low? Can you see anything in the cylinder? It does seem like an unusual symptom for a BHG although the other symptoms match. You could try pressurizing the cooling system with the #5 spark plug out and listen carefully for hissing or gurgling. Good luck.

MJG · 06-19-2011, 02:00 AM

Carbon deposits increasing the compression to 200PSI?
I will suggest a stuck valve.
Pull your cam covers and check #5 exhaust valve.

06-17-2011, 01:58 AM	#1
zyzx2k9 Stock Join Date: Dec 2009 Location: Rhode Island Posts: 10	Weird compression test - is this a BHG?? I've got a 1990 Supra Turbo and was driving on the highway recently, and when I pulled off to park I could feel the car was running rough, really chugging. It was just a quick stop and when I restarted the car (still warm) a TON of smoke came out of the exhaust. It was at night so I couldn't tell if it was white or blue, but it definitely wasn't black. It continued running rough on the short drive home, but notably improved whenever I got the RPMs over about 2200. Smoke was pouring out the tailpipe the whole time, and particularly at lower RPMs. From all I have read in the forums here, it sounds a lot like a BHG. So I took the car in for a compression test and the readings came out odd--all the cylinders had normal compression readings in the 160s, but cylinder #5 was off the charts at over 200. It was tested twice and came out the same both times. Is this consistent with a BHG, or is there anything else that might cause these symptoms? I'm almost ready to take the plunge and replace the head gasket, but I'm holding out hope there might be something more minor that will resolve the problem. Thanks Supra community for your insights...

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06-18-2011, 12:19 PM	#2
El Supracabras 3" Exhaust Join Date: Feb 2010 Location: Chicago Posts: 240	The only thing I can think of that will increase compression is if something (carbon deposits, oil,coolant,fuel) is taking up space in the combustion chamber causing the air to be compressed into a smaller space. If there was coolant in the cylinder from a bad head gasket it could increase the pressure. Is the coolant low? Can you see anything in the cylinder? It does seem like an unusual symptom for a BHG although the other symptoms match. You could try pressurizing the cooling system with the #5 spark plug out and listen carefully for hissing or gurgling. Good luck.

06-19-2011, 02:00 AM	#3
MJG 3" Exhaust Join Date: Mar 2010 Location: Washington State Posts: 125	Carbon deposits increasing the compression to 200PSI? I will suggest a stuck valve. Pull your cam covers and check #5 exhaust valve.