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Luigipepper
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31 Posts
Discussion Starter #1
My MK3 Turbo has been running like crap at boost over 10 psi and has been fouling plugs and sputters. Now for some History on the car:

Upgrades
I have the Lexus upgrade with 550cc Lucas injectors, AFM, Walbo fuel pump, rebuilt head, ARP studs, HKS 1.2mm MHG, upgraded JT57 Turbo, hardpipes, Spearco intercooler, 3" downpipe with a high flow CAT and an RSR 3" CAT Back exhaust, SAFC2, wideband, new wiring harness, etc.

Latest discovery
Since I have been fouling the plugs trying to figure this out; last night I decided to pull off the valve covers and check the compression and to re-tork the head. When I got the first valve cover off I discovered a small amount of radiator fluid in the #6 spark plug hole and a small amount of fluid near it and also up near the #1cylinder? Now I am thinking BHG but I have none of the symptoms, no over heating, runs great until over 10psi of boost, etc?

So my next step was to do a pressure test on each cylinder. To my suprise, most of the compression testing came back with very high numbers. The highest cylinder was 179 psi and the lowest was 158 but the largest difference between any cylinders was around 13 psi. Can you have too much cylinder pressure in the
7MGTE? The rebuilt head was a head off a non-turbo supra and the engine shop used my cams. Could this be the huge pressure increase? I used a 1.2mm HKS MHG when I put her back together. The machinist I used said it would be fine but I want a few more opinions.

Troubleshooting so Far
CPS, Ignitor, Coil Pack, Plugs, Timing of course, AFM electronics module, boost controller, checked all the hard pipes and couplers for pressure leaks, replaced all air hoses, no air leaks any where.

Please help?

:hay:
 

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3,877 Posts
hmm.... I forgot what size cometic HG I used, but after suspecting a BHG for some time, i did a compression test and got 150-155 across the board...

that is pretty high, but I dunno, maybe it's having issues with spark?

what's your gap set to and what plugs are you using?
 

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1,480 Posts
Coolant in the plug galley would have me looking for a leak in either the heater hose at the back of the block or (in your case since there was coolant in the #1 plug position) the throttle body and it's two hoses. The plugs may be shorting.

As for the compression numbers, it could be carbon build up. Did you clean out any carbon deposits when you put the head on? The N/A head is the same as the turbo's, the difference between the two as far as compression goes is the pistons... unless your machinist took a lot of material off the head.

Are you burning any coolant or is it just getting into the plug galley?

Post up the compression numbers in order, it may help.
 

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Street Sleeper
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So my next step was to do a pressure test on each cylinder. To my suprise, most of the compression testing came back with very high numbers. The highest cylinder was 179 psi and the lowest was 158 but the largest difference between any cylinders was around 13 psi.
My maths might not be what it used to, but 179 - 158 = 21 psi
 

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If that urbo uses the same coolant lines as the CT-26, I would check the upper rubber coolant line going ot the hose as well. I once had put a small puncture in my rotten old hose while doing other work, and behold after driving, coolant shot into the valley. I cleaned it up and replaced the hose, but after doing that I would get sputtering at WOT. Basically 12psi or so.

I ended up replacing the wires and plugs with new, and I was back in action. as CRe stated, moisture in the valley can cause weak spark and sputtering like you described.
 

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NO SOUP 4 U
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With other motor work i have run on to issue with anti freeze leaking in to the cylinders. The one with the high compression in it..... it that the one that has the anti freeze in it? If so the high compression might be attributed to hydraulic lock. Meaning a liquid is increasing the compression.

Wedge
 
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