Pete L

Starting a new Post – looking for suggestions / help

The Car:
• 1986 928S 5-speed (early)
• 170,000 Mile’s

Not on the road now for two years because of the problem below

Problem / Symptoms:
• Car starts and idles but not particularly smoothly, motor will not pull / is TOTALLY flat above 3,000 RPM.
• Car will not get past 45 MPH!
• IF throttle is blipped / opened quickly, motor hardly revs past 4000 RPM and goes COMPLETELY FLAT
• 11” if HG vacuum at LH – steady
• Blip throttle, vacuum gauge drops to 2” then goes to 18” then back to 11”
• At idle timing @ 18 degrees ATDC (left side of 0 degree on damper) when checked with timing light. Per Porken stock cruise map, should be around 10 degrees ATDC? Where should the timing be using a indicative timing light on cylinder 1 at idle?
• At 2000 RPM timing at 20 degrees BTDC +/- (Right side of damper 0 indicator when viewed from front)

Recent History & Work:

• Fresh Shell premium gas
• Cam Gears, damper marks and all are lining up. Rotor holes are almost centered in the cam gears
• Rebuilt MAF / LH computer by Electronic. Spare MAF by injection labs when installed results in no change in drivability
• New throttle switch
• Top end vacuum hose/ intake gasket replacement complete,
• New TS II
• Checked all sensor inputs per WSM items for temp 2, MAF operation etc. at LH/EZF - all in range
• Checked coils, checked per WSM and OK
• Checked rotors, caps, wires and all good
• Checked timing belt – perfect condition, all marks align at TDC
• No smoke or whips from exhaust, no apparent oil burning
• Replaced fuel filter
• Checked fuel pressure and volume per WSM – perfect
• Did compression test 150 / 160# cold all cylinders
• Did Leak Down – all cylinders’ around 10% leakage (cold)Removed vacuum line from LH – did not see change in timing
• Smoke test - result- smoke coming out from vicinity of driver rear valve cover - replaced valve cover gasket and rear, still getting smoke from I think from rear cam plugs

Ideas of what else to look at? Could the LH be regarding the timing so far back that the vacuum is as low as it is? At any rate, I am looking to sell the car as I have had enough fiddling with it since I first bought it in 1993

Mrmerlin

did you replace the idle control valve with a new part?
did you reset the MAF mixture and then set the idle speed using the test port bridge?
did you replace the temp 2 senor Connector?
Did you replace the TPS short harness?
did you replace the crank position sensor ?
Did you use all Bosch parts for the ignition system and crank position sensor?
Are the plug wires new?
have you verified the firing order?
Did you replace the O2 sensor with a new factory part?
have you checked the fuel dampers and FPR to verify they are not leaking fuel via the vacuum lines?
Usually all of the things listed can cause running issues,

Imo000

Are you 100% sure the timing is not off?

Mrmerlin

yes some of the remarks about timing at ATDC dont make any sense,
might you have the damper turned around?
Do you know where the number one plug is?
#1 passenger side front.
#8 is driverside rear

in the picture posted,
the damper marks that the timing light will show should be to the right of TDC
Oh if your numbers are not in the same position as these then the damper is turned around

Pete L

Thanks for the reply's. I've been wrenching on my 928 since 1993 and done timing belt at least 5 times. I am very familiar with he car. My answers are in CAPS

If 10 degrees AFTD is incorrect timing at idel, then what the hack can cause this?

yes some of the remarks about timing at ATDC dont make any sense,

might you have the damper turned around? NO NOT TURNED AROUND

Do you know where the number one plug is? YES

Today 12:27 AMdid you replace the idle control valve with a new part? NO, FUNCTION PROPERLY WHEN JUMPED OUT - WOULD NOT CAUSE 11" VACUUM PROBLEM

did you reset the MAF mixture and then set the idle speed using the test port bridge? YES WITH STARTING MAF POINT AT 393 OHMS

did you replace the temp 2 senor Connector? YES ALL CHECKS AT LH WITH OHM READINGS AS WELL

Did you replace the TPS short harness? YES. TPS CHECKS AT LH AS WELL FOR WOT and CLOSED

did you replace the crank position sensor ? SEVERAL YEARS AGO. PIG-TELL IS NOT BRITTLE. ITS IS NOT CAUSING THE 11" VACUUM PROBLEM

Did you use all Bosch parts for the ignition system and crank position sensor? YES

Are the plug wires new? NO BUT ALL OHMED AND NO FIRIFLIES IN THE DARK

have you verified the firing order? YES

Did you replace the O2 sensor with a new factory part? IT HAS LESS THEN 1000 MILES

have you checked the fuel dampers and FPR to verify they are not leaking fuel via the vacuum lines? SEVERAL TIMES

Usually all of the things listed can cause running issues,

hwyengr

Have you verified with something long and thin sticking into the plug hole for #1 that TDC on the damper is really TDC for the engine? They've been known to twist with age.

Mrmerlin

idle control valve is a wear item and should be replaced every 60 K miles.

throttle position short harness has a failing connector where it meets the car side of the harness
this should be replaced.

temp 2 sensor connector should have the wires cut back a few inches and new connector installed.

spark plug wires if more than 10 years old should be replaced and routing verified.

O2 sensor should only be replaced with a factory part not a universal part.

where are you pulling the vacuum reading from? try the front damper port

OTR18WHEELER

...I'm tired of the ezk, lh, maf, whatever go to replys.
...none of this applies to every car.
Most problems are caused by poor maintenance over the years., hack jobs, and sell it to the next newb.
Am I the only one here that has a +100k mile car As a DD with all original stuff?
...

zekgb

The vacuum reading is puzzling as I got 17" even when running on seven cylinders with the burnt valve in my avatar. Have you pulled plug wires at idle to see if you have any dead holes?

Mrmerlin

have you tried another vacuum gauge ?
are the distributor caps new?
if so swap in the old ones one at a time and test

John Speake

The vacuum line goes to the EZ-F (ignition ECU) not the LH. But 10inHg is much too low !

17 -20 is more typical.

That would account for the timing being off.

Are you sure it's running on all 8 ?

Landseer

Clean the injectors.

Pete L

Appreciate posts / answers

Questions / theory
1. is EZF buggered up on retarding timing 20 degrees? I will email Rich at ELectronic and ask him, he rebuilt my LH
2. Could the timing ring on flywheel slipped?

Landseer - injectors were rebuilt / flow tested when I did the top end refresh

John - its running on all 8, have spark and fuel to al cylinders, did compression and leak down all OK.

TrMerlin - new rotors, caps, three different vacuum gauge used and checked at LH, fuel dampers and therm switch. Also ISS, TPS three wire harness, wires etc are all fine. None of this would be causing the low vacuum -

928S MN

Do you still have the original exhaust cats in?

Could they be plugged?

zekgb

Other stuff you haven't mentioned checking that could cause multiple cylinders to misfire.

• Ignition Amps
• Cam chains out of time. Have the cams ever been out? What was the condition of the tensioner pads last time you had the cam covers off?
• Plugged Cat

Worst comes to worst you can bring it down to Sharktoberfest where there would be plenty of known working parts to swap in and out.