928S4 Bad performance off throttle

Eturbo924 · 03-10-2009, 06:26 PM

Ok need some help guys.

I just purchased a 1987 928S4 automatic.
I picked it up in NC and drove it home. It performed very well for the first 500 miles or so. Then it started to heat up under the car where I figured the Cats should be. (turns out there are none on my car) The area below the shift lever. It was so hot I could not stand driving with out the window at least partly open. I did look under the car and did not see anything.

Anyway... about 600 or so miles into the 875 mile trip the car would not idle well when shifted into gear. It kind of chugs... or surges. Sounds like it is missing a beat or two. If you shift it into neutral it smoothes out a bit but still not perfect. If you open the throttle a bit it seems to be ok... and while you drive it is ok as well.

So... when I got home I suspected maybe an ignition wire was shorting out. I traced them all and did find one and it might have blown the crap out of the corner of the left bank valve cover with arking or the cover was damaged by the PO. Did not see this of course on initial inspection because you had to take off the air intake tube and move the wire to see it. So that is potential issue.

Here are other thoughts.
Bad O2 sensor? The one in the car looks relatively new but I have no records of it having been changed. Though... most of the exhaust looks new and so does the O2... but that excessive heat could have killed it?

Next... that hole in the valve cover... while needing a repair (or replacement) could it cause the surging?

The last thing. The voltage never seems to be right (battery). It was always around 12 volts when running and seems to fall just below it some times. When the car is doing the surging it jumps between 10 and 12. Only once did I see it at 14.

Help?

Oh all belts were done at 98K miles it now has 115K. Looks like new alternator.

MPDano · MPDano's Garage

Hmmm, did the seller disclose any problems with the car? It almost seems as if he was also chasing a problem and replaced a bunch of stuff he also thought could have been the problem. Was it a killer, too good to be true deal, since this could be why. Just sayin'.

Griffinroydonal · Griffinroydonal's Garage

I would like to be kind and ask where you picked up this car in N.C. ? I will be nice and you could even PM me if you wanted too. I am not trying to start a problem but might have some insight about the car.

I would have loaned my tow vehicle and or Dolly so you would not try and drive it home. I have made the same mistake and been found on the side of the road more than one time. Been there -Done that - Never thought it was any fun. I wonder if all the lining /deadning plates are in place under the car as the heat from the engine would be the only thing to warm it up in that spot and I am suprised the enging would run at all after it heated to that point.

Griffinroydonal · Griffinroydonal's Garage

Take the valve cover off and send it to me I will repair it or offer you a cheap replacement. Sorry you had so much trouble !

Danglerb · 03-10-2009, 11:15 PM

First thing to check on a newer 928 auto is the crank endplay. The pinch clamp on the torque tube can "migrate" putting a lot of pressure on the flexplate, which forces the crank forward and destroys the thrust bearing on the crank.

Dean_Fuller · 08:01 AM

^^^ and how about a photo of the valve cover area your talking about. If its a HOLE then I assume your losing a lot of oil....check the level. Over that far a drive and it was fine to start you may be very low....thats not good.

Eturbo924 · 03-11-2009, 12:29 PM

Hey all...

Hmmm... deal was decent but took some time to get it.

It was from "Exclusive motors".... any insight? www.exclusive-motors.com

The car ran well at time of purchase. Started right up and other than a bit of noise from the exhaust under the center of the car it seemed quite good. Of course I had just a horrible flight with delays on delays and missed connections and such... so all I wanted to do was get the car and go. My mistake.

Funny normally I am quite picky... I am the one that others take along to be the pain who finds everything... but in this case I no longer cared. Ah well.

So the hole in the valve cover. I will take a shot of it when I get home. It is not leaking any oil out of that area.

All the heat shields are in place. I crawled under her last night. The exhaust was not buttoned up correctly at the seams though. I think I have that corrected now.

The O2 sensor does look new but the heat coming from that area... might have damaged it? Funny the engine temp never got anywhere even close to 1/2 way up the guage.

Oh and as I said. It ran perfect for 500 miles or more before this started.

Hey anyone got a decent set of wheels for this car? All I really need are one front flat dish and one rear. Yes... PO must not have been so good with the left hand turns. Both wheels on that side were curbed.

Thanks

Eric

lizard928s · 03-11-2009, 08:39 PM

Eric,

Engine temp and exhaust temps are two different things.

As said check the crank end play!!!

As well replace the regulator on the altenator.

Eturbo924 · 03-12-2009, 04:08 AM

Is the crank end play the same issue as releasing the tension on the flex plate? I was planning to do this over the weekend.

So... any thoughts on the surging?

You think that is the crank play... or just some thing all 928 owners need to address?

Danglerb · 03-12-2009, 08:30 AM

Al late model automatic 928's need it checked, and its more than checking the flex plate. Checking the flex plate and releaving any tension on the pinch clamp shows whether or not pressure is on the crank now. Checking crank end play is to see if the thrust bearing was damaged in the past.

No guess on the surging, could be a variety of things. What I think works best is to take a restoration approach to the 928, and go in and refresh everything in each area that gets opened up. Pulling the intake and doing all related hoses etc. is a good place to start, especially all fuel related lines.

Xlot · 12:59 AM

Quote:

Originally Posted by Eturbo924

Is the crank end play the same issue as releasing the tension on the flex plate? I was planning to do this over the weekend.

So... any thoughts on the surging?

You think that is the crank play... or just some thing all 928 owners need to address?

The heat from the exhaust is worrying - especially if the car is running rough. On later cars (89 or 90 onwards) there's a relay with LED's in it that lights up when the car detects low exhaust gas temps, and which causes the injectors on that side to not fire.

On 87/88's, there are no exhaust gas temp sensors, and thus there's no way for the car to know when its not sparking on either side. The result is it pumps air and fuel into the manifold, which results in an exhaust fire.

The single most likely cause for it to happen is a loose coil lead from the coil to the distributor cap. Check them both, as well as the plug leads, and make sure the ground leads for the coils are attached to their bracket.

Sort that out first - if the cars running on only 4 cylinders its very rough and idle will be lower (had it happen to me briefly last week at the AC tech's - he knocked the coil lead when undoing the high-side pressure valve after charging).

If its only 1 or 2 cylinders that aren't firing you'll get some fuel passing through and it'll run rough, and probably burn - in which case check all the plug leads, in the dark to check for fireflys.

If the surging isn't related to not firing, then it could be a number of things - most likely is a vacuum leak somewhere like the rubber boot that holds the MAF to the throttle, or one of the many vac lines and breather hoses around the intake.

Also worth checking:

Temp II sensor - its the sensor on the right-side of the car on top of the coolant bridge just in front of the manifold (note: porsche convention for Left/Right is as seen from the driver's seat - so right side is the US passenger side). If the sensor shows open circuit on either terminal when put to ground it needs replacing.

Idle Stabliser valve - this is underneath the intake, but you can try cleaning it with WD40 by spraying into the appropriate line just by the throttle assembly. If its sticking idle will surge.

Throttle Position Sensor - there's a test routine for the sensor in the workshop manual that indicates resistance at various positions. Like the ISV its a pain to reach, but you can measure signal at the LH plug in the passenger footwell without taking the intake apart. Most TPS's I've seen on S4's have failed on the high side, but the idle switch still works, but it could be the culprit. (the WOT side is repairable without buying a new sensor)

First order is to sort out the plug leads and make sure you're firing on all cylinders - dumping raw fuel into the exhaust is a short trip to a fire!

Checking the crank end play and releasing the flex plate is just routine on auto 928's - if your car has Thrust Bearing Failure it would normally have shown sooner in the drive than 500 miles, unless its a horrible coincidence.

Eturbo924 · 03-13-2009, 10:39 AM

Ok... now strange enough... the car stopped doing the surging... but the idel is now too high when not in gear. It is around 1150. So the trans is a bit rough when shifting from N to D or R.

Once in gear it settles around 1000 if your foot is on the brake.

So... ideas on why this is?

The only thing I did was clean the ground at the battery.

Danglerb · 03-13-2009, 11:43 AM

High idle, bad idle stablizer valve and/or vacuum leaks, and/or with the dirty battery ground some previous person set the idle high to compensate.

I think the OP mentioned no cats, so heat isn't likely rich mix going to cats, unless it really does have cats.

**** Sound to me you just need to add a word to the 87 928 S4 .... "restored". Which end you starting at?

Eturbo924 · 03-13-2009, 12:54 PM

The 924 is restored.

The 928... just starting.

It definately does not have cats... there are straight pipes from the headers to the rear mufflers.

I had messed with one of the coil packs last night. The wire coming out of it ... I had felt was not routed correctly. But... it did not seem like it was not pushed all the way on.

So I guess I need to look for bad vac lines. Think it might be the valve I have in another post? The idle going to high now that is?

Thanks everyone I am new to 928s and need all the help I can get!

Eric

usfromflorida · 03-13-2009, 04:50 PM

A high idle is a symptom of unmetered air getting into the intake after the Maf seal, reset it, check all large hoses to the T-body and brake booster. Roger at 928srus has a cheap leak tester, under $30.00 for checking vacuum leaks.

Danglerb · 03-13-2009, 05:02 PM

Quote:

Originally Posted by Eturbo924

The 924 is restored.

The 928... just starting.

I'm suggesting that rather than trying to run down each of many little issues, you might be better off starting at one end and fixing everything one area at a time.

Griffinroydonal · Griffinroydonal's Garage

I was at exclusive motors several weeks ago and bought all the 928 parts we could find in the back store room. I live 1 hour west and chances are you came very near my house. I am not sure which car you bought but I spent quite a lot of time with them that day. I really love "Papa Smurf" Blue and super bad - Cant beat that. All of the cars I saw for sell looked to be in great condition and I hate you had problems. I always can help with transport in a case like that and all contact info is in profile.

vanosman · 03:58 PM

Quote:

Originally Posted by Danglerb

I'm suggesting that rather than trying to run down each of many little issues, you might be better off starting at one end and fixing everything one area at a time.

KRB will drive it to the burn pit for ya .
"Iraq For Sale" KBR drives a 18 wheeler into burn pit for just a blown tire, no oil, fuel, air filters allowed, no spares, little maintenance, double bill taxpayer for new truck. Charge Taxpayer, force KBR driver to deliver 1 bag of mail on hostile, IED roads.

The executives have 22" spinners on their H2's with nav screens and subs, etc. They are lined up in a row in the film

http://motors.shop.ebay.com/items/Cars-Trucks___928_W0QQ_catrefZ1QQ_flnZ1QQ_fromfsbZQQ_tr ksidZp4506Q2ec0Q2em1

Eturbo924 · 03-14-2009, 07:25 PM

Ok quick update.
Tonight the car died on the side of the road. This is just after a quick but not outragious launch. So things may have shifted around a bit.

So... took some doing but managed to start it and keep it running to get home. I was only about 1.5 miles from home anyway.

So get it home and idle is back to the surging and lower than before.

I let the car sit while I thought for a while. I then took the air cleaner box off (found the K&N filter is dry and likely letting past too much crap but that is another story) and was inspecting the fit of the MAF (that is just below the air box correct? And.... hmmm... it is way loose. I could just pull it up and out of its connection. So... figured I was home! I tightened the connection and put it all back together. Adding in some bolts the PO forgot to put on and started it up. Crossing my fingers for a miracle... and ... dou! No surging... but still rough idle. There is a definate misfire. I just do not know which cylinder it is.

I guess I have to pull the plugs and inspect each. I have already gone over every one to check for good connections. Might have to just replace all the ignition wires and plugs. They are Nology wires. Anyone have any experience with these?

Also might take the MAF out and reseat the boots again to make sure I got them right.

Ah the fun of it all. Plus... I still have to inspect the flex plate and the associated play discussed above.

Oh and I will of course be going over the other suggestions above. I have done many already.

Must sleep now....

Danglerb · 03-14-2009, 07:44 PM

Two ways to check the wires, in the dark with the motor running spritz some water over the motor (a mist) and look for sparks etc., and/or pull each wire and check with a meter (mine are about 2.9K, not sure if its different for your model or Nology).

No idea about Nology, but I don't plan on switching from Beru.

Sorry to beat a dead horse, but chances are good nothing that hasn't broken has ever been changed on your car. When you work in some area, you move stuff around and old hard hoses that sort of sealed, don't seal as well. If you don't replace everything, you can set two new problems in motion for each thing you fix.