Kevin in Atlanta

Recent work:

X-pipe and cat delete and top end refresh. Injectors were refurbed - before and after changes were not that different.

Not much of delta as the current owner didn't really own it long enough before he tossed the exhaust items above on it. So, didn't really know it was down on power until the exhaust changes.

He decided to do a top end refresh in hopes this would fix the situation. It didn't.

We've swapped in known good GT LH computer and rebuilt MAF with no improvements.

Service records show recent spark plug wires and distributor caps prior to purchase.

The flappy twitches at start up.

Here's the symptoms:

The car does not come alive until it hits rpms hit 4k. Before that you can give it half throttle without any real response.

There is a driveline shudder when starting from a full stop as you slowly release the clutch. I was thinking it was the clutch slipping - maybe not.

I've read a bit and am wondering if the hall sender could be at play here.

We're going to check the cam timing this week as well as do compression testing.

Any suggestions appreciated.

Ducman82

hows the timing?

Kevin in Atlanta

That's next on our check list.

Ladybug83

Throttle cable adjustment?

Mrmerlin

did the CPS, knock sensors, hall sensor, TPS, ICV ,parts all get replaced with new Bosch parts>?
Put the old caps back on one at a time run till heat soaked then swap in the other.
Did the ignition wires get replaced?

dr bob

Kevin-
You work on enough cars to deserve a diagnostic tester. Almost any (Porsche/Bosch, Theo's or John Speake's) will tell you how the various sensors are doing. For your subject car, the Hall sensor a would top my list of things to look at. Followed by knock sensors. Failure of any of those will pull timing under load.

Kevin in Atlanta

^^^^ That is where I am going next. I have been putting that off too long.

worf928

Hall sensor would be probable culprit for flacid high-rpm function. A dead Hall sensor won't, usually, affect function below ~4k.

Slugish low-rpm function, given recent work, seems more consistent with over-fueling: open loop to TEMP-II, engine vacuum sucking fuel into intake via busted dampener, maybe wrong injectors, etc.

But, yeah, if you are going to work on late model 928s you should have a tester.

Popo928

I had similar problems on an 84 euro. Our similarities are that there wasn't any known history so you don't know what kind d of crazy things they've done. The problem ended up being the P.O. had replaced the chips with ones speced for 85-86. Clearly the maps between the two were way off. I sent John Speaks the numbers that were on the chips and he confirmed they were wrong. It an easy check to do.

dr bob

Double-check your cam timing too. Off a tooth will do what you report.

Kevin in Atlanta

According the service records hall and knock sensors were replaced in the last 1000 miles.

Cam timing is where are going next.

Kevin in Atlanta

Warm engine. Timing belt only as 1k miles on it. Tensioned it properly.

PS cam timing dead nuts @ 0 degrees, DS 6 degrees retarded.

Kevin in Atlanta

Owner reports that the car is performing even worse after we advanced the DS cam timing to 0 degrees. I think it's time to check the compression.

SwayBar

I have installed 32v cams many times successfully, but I do not understand what you mean.

6 degrees is 2 teeth on the cam gear which would be way off.

Kevin in Atlanta

Used the Pk32'r to dial in the cams and the DS cams were 6 holes retarded according to the tool. I hope I am saying that right.

Another disconcerting observation was that the DS cam nose had evidence of somebody using a large socket to smash the cam nose. I am sorry I did not take a picture of it. I cannot imagine why that was necessary.