86 has issues-pops and bogs under high boost

Probably off-topic, but some of the time when my 86 SVO(5-speed, intercooled) gets near 14 or 15 psi, it pops and bogs down, and makes no power. If I let off the gas sometimes it will recover, sometimes it will stall. This started happening suddenly about 2 months ago. It is totally random, sometimes it will run strong to redline, sometimes it just gives up. It runs great on the low boost (10 psi) setting. I've been searching websites for weeks trying to find the answer, I'll list out what I have done to try and find the problem:

Happens with the KS connected or disconnected.
Exhaust is new including Catalytic convertor, and straight-through muffler.
I've had 4 different sets of spark plug wires on the car (Motorcraft X2, Bosch, Accel, MSD), and 4 differnt sets of plugs (Autolites and Motorcraft, tried gaps anywhere from .020" to .035").
There is a spring in the VAM hose.
Engine mechanically is in good condition (50K miles), compression is 150 PSi in all cylinders (Warm). Cam timing is correct and base timing is 10 deg BTDC with the spout removed.
After checking all the pinout voltages, doing a KOER test (pass 11), KOEO test (pass 11), and doing a wiggle test, I'm convinced (for now) that the wiring is fine. All the sensors were within range so I'm convinced that they are fine also. Parts I have replaced with known good units include the following, VAM, TP, BP, ECT, Distributor including PIP and TFI.
I've driven many miles with the engine acting up and the fuel pressure gauge plastered to the windshield, the fuel pressure is good and high when the engine acts up. I replaced the injectors with a set of good injectors with no change.

I'm completely out of ideas. Can anyone help? Could it be the computer?

thanks, Jeremy

Jeremy:

Welcome ! I'll try to help, however you can also go to www.turboford.org for help. There are several SVO guys there as well.

Since you said FP was good under boost I'll skip that but it was my first thought.

Check for cracks in you IC hoses or loose connections ?

What vac readings are you getting ?

Could also be a bad TFI/PIP. Did you get at Motorcraft or aftermarket one ?

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Dan Eaves
88TC 5spd, Crower 5.5" Sportsman Rods, Short Wiseco Pistons bored .030" Over, Ported Head with Polished Combustion Chambers, Gutted & Polished Upper, Ported & Polished Lower, Polished T/B, Ported E6, SVO T3 .63AR Turbo, Bosch Bypass Valve, 3" DP w/No Cat, 2 1/2" DynoMax single cat back w/DynoMax Super Turbo Muffler, RR Cam, K&N in Fenderwell, Gillis Boost Valve, Centerforce I Clutch, Removed A/C, Polished Wheels, Polished Valve Cover, Polished Crank and W/P Pulleys, Walbro 255LPH HP Pump, Kirban Adj FPR, and the DAMN Heater Core is new too !

NATO MEMBER (Vice Chairman...if it's a vice...I deal with it)

[This message has been edited by Dan E (edited 06-04-2003).]

Dan E,
I've had the intercooler off 90 times(!) since this thing started running badly. The hoses are aftermarket and in great shape.

Vac is about 16 inches of mercury at idle, and steady. Let off the gas on the highway and it's 18 or 19.

PIP and TFI are motorcraft.

Unless you are using a non-stock cam with too much overlap (like the A237), your vacuum readings are low. You should see 18 to 22 at idle. You may have a leak or your cam timing might be off.

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NATO Member. it's not a vice, it's an obsession
Good judgement comes from bad experience, and a lot of that comes from bad judgment.
88 TC X 2, 86 SVO, mods list at
http://www.turbotbird.com/showroom/pd_88tc.htm

Apart from somewhat low vac...

My next guess is a possible bad VAM.

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Dan Eaves
88TC 5spd, Crower 5.5" Sportsman Rods, Short Wiseco Pistons bored .030" Over, Ported Head with Polished Combustion Chambers, Gutted & Polished Upper, Ported & Polished Lower, Polished T/B, Ported E6, SVO T3 .63AR Turbo, Bosch Bypass Valve, 3" DP w/No Cat, 2 1/2" DynoMax single cat back w/DynoMax Super Turbo Muffler, RR Cam, K&N in Fenderwell, Gillis Boost Valve, Centerforce I Clutch, Removed A/C, Polished Wheels, Polished Valve Cover, Polished Crank and W/P Pulleys, Walbro 255LPH HP Pump, Kirban Adj FPR, and the DAMN Heater Core is new too !

NATO MEMBER (Vice Chairman...if it's a vice...I deal with it)

I've swapped VAMs with a known good one, I've also checked the voltage sweep with a voltmeter, and it is smooth with no dead spots.

I'll re-check my vacuum and report back.

thanks
Jeremy

Well, I checked the vacuum again last night with an autometer boost/vacuum gauge, probably not the most accurate gauge in the world. It was right at 16 inches of Mercury at idle. I disconnected all of the hoses off the intake, plugged em, and the reading did not change. I also sprayed around every gasket surface and the throttle body pivot with WD-40 with no change in idle. Where else should I look for a vacuum leak?

I triple-checked the cam timing and it's spot-on.

Jeremy