Pete L

The Car:
• 1986 928S 5-speed (early)
• X Pipe, Porken S400 chips, recent MAF rebuild by Injection Labs
• 170,000 Mile’s

Problem / Symptoms:
• Car idles OK, will not pull / flat above 3,000 RPM
• Wide Band AFM is showing 13 to 14.2:1 when running on street (little rich?)
• Only getting 11” if HG vacuum at LH

Recent History & Work:
• One year ago car died on the road due to gross MAF failure. Believe this was caused by the MAF connector. Reason. After pulling 6 pin boot, every wire was bare and touching
• Injection Labs rebuilt the MAF ( Kevin stated it had a gross failure) installed spare LH 2.2, car started right up
• Also believe this also took out the LH 2.2 – sent out to have it rebuilt by Electronik Repair a week ago - they found a bad resister that is part of the MAF circuit.
• Between last June and this June car ran great.
• Car run at Willow Springs in March (big track) over 140 track miles that day, car had never run better, great power (first time on track with X pipe and Kens chips)
• Car taken to Dyno in June, first pull clean to 6,200 RPM, 290 RWHP, 12.5 AFR @ WOT but during second pull at 3,500 RPM car ran flat, lost power, missed, began to run very rough, would hardly idle, stopped test and drove it home. Car was not over revved
• No “blown up engine” noises noticed, no metallic grinding, oil in exhaust, smoking, overheating, no blow by in oil fill when cap removed
• Last time car lost power at WOT (at least as I recall it) was due to throttle switch – so checked switch operation at LH for idle and WOT - all checked
• Checked all other WSM items for temp 2, MAF operation etc. at LH/EZF - all in range
• Checked MAF wires from 6 pin at MAF to LH /EZF via test light test and wiggling, all seemed in order
• Checked coils, checked per WSM and OK
• Checked rotors, caps, wires and all good
• Put indicative timing light on each plug wire and got a flash on each wire
• Checked timing belt – perfect condition, all marks align at TDC
• Car still running like crap, hooked up vacuum gauge only seeing 11” Hg
• After seeing 11” in vacuum, sprayed starter fluid around intake spider / head and car stalled when spayed in vicinity of intake tube 5. Oh a big vacuum leak? Decided to pull intake and did complete intake manifold gasket R&R, replaced all vacuum and crankcase ventilation lines
• Car started right up after intake R&R, running better, no stalling / worse running with spray test but still only 11” of Hg vacuum when running
• Still no power after 3,000 RPM – just very flat running
• Car is not over heating, normal oil pressure, smooth running
• No smoke or whips from exhaust, no apparent oil burning
• Thought vacuum loss could be at brake booster, but still have power brakes that feel normal
• Car does not burn oil. Typically 2,500 miles before I need to add a quart

Questions / Next Steps
• Yes, realize I need to pull plugs - plugs when pulled 5 weeks ago prior to dyno were perfect and less than one month old.
o Would toasted plugs or cylinders not firing cause low vacuum?
• Any other ideas what to check in response to low vacuum at idle?
• Pulling plugs and will do leak down / compression – but motor, at least up to 3,00 rpm is running smooth and does not seem to be “blowen up”
• Check out and install rebuilt LH 2.2

Sorry for long post, searching for correct items to chase – and I am stumped

Lizard928

Check plugs and do a leakdown test on the engine to ensure that all valves are sealing.

Pete L

Update July 12th.

Performed compression test - all cylinders 155# to 165# (dry). All plugs look good. Doing leak down later today but I believe engine internals are sound based on compression test

Wonder if the spider at intake / head interface is warped?

I will do a write up informing of the final fix

Shane

You should be getting right around 17"HG at idle. Last one I checked had 17.5 "T" into the vacuum signal to the brain.

SMTCapeCod

removed ramble, which was intended for entirely different thread. Sorry- carry on!

dr bob

Pete, your symptoms point to a partially-collapsed catalyst. Probably due to the hard dyno pull? There are ways to tap the exhaust at the oxy sensor bung and get a back pressure reading on a gauge, but it might be easier to sub in a test pipe to be sure.

My two cents.

Pete L

Update

Dr Bob, cats are not on the car, x pipe only. Did the dyno for "fun" and to see what increase in HP/Torque from kens Chips and validate what my A/F meter was reading. Saw 290 HP on first pull.

Did the leak down today and worst cylinder was 8%. Internal engine is thus presumed good.

Smoke test tomorrow of the intake etc. It has to be a big vacuum leak at the spider in my opinion. But darn, just changed out the gaskets etc and the car did not stall or run differently (as it did before I replaced the intake gaskets + under spider hoses) after spraying staring fluid all over the top end of the motor after I put it back together.

But the 11" at idle of vacuum is just not right + the car is running like CRAP

PorKen

Possible a cam slipped, or is broken? Check the position of the cams vs the gear - the distributor rotor bolt holes should be roughly centered in the slots (or put a 32V'r on there).

Mrmerlin

as Porken said the cams have lost time with the crank,
even though you have good compression 150,
it should be higher to get that kind of HP 290.

That said I would consider removing the timing belt covers and then inspect the timing of the cams to the pulley.
if no joy then remove the cam covers and look for broken teeth on the gears at the chain drive,
or a broken snout on the driver side cam

76FJ55

unlikely, but another possibility is a break in the driver side injector circuit. the O2 is typically installed in the right leg of the X so may not see a loss in fuel on the left bank. Idle control valve would hold idle speed but opening to allow more air (low vacuum) but power would be way down.

Mrmerlin

read this it will be a better guide to follow

http://www.google.com/url?sa=t&rct=j...,d.aWw&cad=rja

ramcram

If it's a big vacuum leak, poking a stethoscope in and around there should pick up a huge hissing?

Pete L

Appreciate the responses! Been busy on a home improvement project, work and was involved in an accident with my daily driver so no time to do much recently

Here is an update

• Car still down on power (greatly down) at > 3000 RPM but starts and idles fine – sort of drivable
• Motor is sluggish / flat when blipping throttle at > 3000 RPM
• Car just passed emissions (put the cat back on that I “cleaned” so I could register the car, will start new thread on that topic). Emission results were best – greatly better (lower) HC and NO by 50% than ever before in the 20 some years I’ve owned the car
• Smoke Test – one leak, at power brake booster grommet and T fitting – new one ordered
• Other minor vacuum leaks at throttle body / spider T fixed
• Vacuum at idle is now 12” measured at brain @ 700 RPM, but increases to a steady 17” at 1,200 RPM. Hummm
• Fuel Pressure – checked pressure (not volume) got 4 bar
• SMTCapeCod –based on smoke test, spider/ intake runners where bolted to head are sealed – was my original suspension
• 76FJ55 – Based plugs looks like all cylinders are firing, but good thought to check again. Question, how does one get a noid light on t FI to check on 86???
• Ken / MrMerlin – Checked cam drives etc. by pulling covers and all looked good and in alignment. Ken if cam was broke and engine run, would have a lot of very poor running due to inference I presume, so assuming cam is not broken, car idles fine

Next Steps

• Install another computer – just had my spare rebuilt. Car feels down on power just like when I had a failed TPS, but I am getting signal at computer when TPS is tested
• Replace fuel filter – could it be clogged – but why would that effect the at idle flat revving up described above?
• Get MAF checked by Kevin (swapped out the recent rebuilt unit from Kevin with an old unit I had, car runs the same)

Tiger03447

@ Pete L; Check the TPS very closely and resistance all the way through the coil. could be that the TPS wiper is not contacting the resistance coil and not changing the input to the DME. Swap it out first, then check out the old one...just a thought..Thanks, Tiger 03447

Hilton

What fuel pump is installed on the car? Have you verified the part number is the correct one?

If it is the correct one, have you checked the pump delivery volume against the specs in the WSM?