Brambleworth

Bought a 1989 928S4 Japan delivery on BaT last year. Car arrived and it was a disaster. After settling with the prior owner. I had a running car with a lot of issues. Decided to undergo a heavy restoration starting with a complete interior change and then an intake refresh along with a harness rebuild and almost all new sensors, hoses, vac lines, injectors, alternator, battery, MAF, ISV, ps pump, belts, fan harness, foe harness, fuel
pump and filter etc. Car had a water pump and belts done a year prior to purchase. All parts and rebuilds were purchased from Roger.

Items I have not changed yet. O2 sensor, temp sensors in heads, coils. When I attempted a startup I had a no start, had the tps and cps connectors backwards, switched them and it started. Problem is that it stalls on acceleration. I have taken it over 3000 rpm in neutral with a gentle throttle application to check the flappy valve. Car will idle and drive around at an idle, but any gas and it stalls. There seems to be a loud “huffing” sound around the back of the engine when it stalls out. After assembly I smoked the engine for 1 hour with no leaks and had an almost 2 minute leak down when pressurizing the intake to 3 psi. Today I unhooked the exhaust at the manifolds to see if I developed a clogged exhaust system from a mouse nest. Car still stalled on acceleration. Exhaust does stink from sulfur. Scoped the cats and they don’t appear clogged although was some curled up wire in front of both elements. Have spark in cylinders on both banks. No lights on EZK relay. Trany vac line is not hooked up yet but is capped. All fuel
lines and regulators and dampers changed.60 psi fuel pressure at rail.
Any thoughts would be appreciated.
Thanks
Ted

hwyengr

Edited, i missed the part about it running before the refresh, and suggested LH brain. But the odds are slim it failed exactly during the rebuild.

Brambleworth

It was shocking that it ran. Harnesses were patched and bare, sensor connections were cracked and exposed.

Speedtoys

What happens if you unplug the MAF?

If nothing...suspect the maf is entirely bad, or the cable to it...thats how they run in safe mode with the maf unplugged..

hwyengr

Man, that’s my BaT nightmare fuel, right there.

Kevin in Atlanta

Did you mess with the spark plug leads? Can you verify they are correct?

Mrmerlin

put your LH into a known good running car .

after I did a intake refresh and HGs to my 88 project ,
I had a similar issue,
It turned out the recently rebuilt LH had been fried from an over voltage event,
the engine would start and idle,
but adding gas it would stumble and finally stall around 2500 to 3K RPM.

https://rennlist.com/forums/928-foru...and+prix+white

Brambleworth

Will check the plug wires again. I am starting to think that the error I made when I mixed up the tps and cps plugs may have damaged the tps, cps or LH. Also going to test the MAF harness today.

linderpat

Which BaT car was it? I couldn’t find it.

Brambleworth

Search BaT for Brambleworth. Quite frankly, every car I bought on BaT was a disappointment and expensive to get into reasonable running order. Really no different than eBay in the end. I think BaT needs an after sale report to flush out unscrupulous sellers.

Brambleworth

Spark plug wires new and in correct order. MAF harness connection voltages correct with key on. Started with MAF unplugged and it runs the same way, idles and stalls on throttle. Suspect LH now.

Koenig-Specials 928

For what it's worth, here's another data point.
3 weeks ago I suffered a no-start condition
With the help of an ST2, Jim Corenman diagnosed a bad Maf connector (it looked ok but was shot internally close to the terminals)
I installed a new connector from Roger and the car fired right up