dukenukemx

My 85 928 drove fine for 30 minutes and then I parked it for an hour and went back to start it, only to have it misfire like half the cylinders were working. I pulled over to shut it off then start it back up and it ran just fine. This has happened before but I think it just eventually ran fine after a few seconds. I'm not sure what the problem is since I didn't get a chance to determine what the cause is. I wanna fix it before I get stuck somewhere. Is this maybe a symptom of a failing coil? Maybe ignition module?

Speedtoys

I get this on my S4 now, used to be rare, now more common.

Runs fine, go away, come back..wont really start, tries..but if I put my foot to the floor a cloud O black smoke and ZOOM it fires right up.

It's flooding itself to death on start, sometimes, like once a week.

And sometimes it does this also if Im in idle (stop light, stop and go traffic...)and enough pressure on the gas to leave idle mode, and it does the same thing..suddenly coughs stumbles and dies by flooding...if I go neuitral and STEP on it it will sputter and clear itself, all is well again. Or just let it die and start it WOT to clear it...then its fine for days.

Maybe worse when warm out, like >70 degrees than below it. Will even do it on cold startup...but the odd part is that it will be IDLING perfectly, then flood itself when you touch the gas.

C531XHO

I had this issue on my 89gt, sometimes ran well sometimes appeared to go on one bank. Traced to broken king lead. Check both ends and i guess resistance. Mine had snapped at the distributor cap end, not obvious unless you inspect the connector inside the rubber cap or remove distributor cap/look up from the ground at the female socket

Gary Knox

Frequently a bad lead wire (or poorly connected wire) from the distributor on one side on 32V motors (only ones I'm familiar with, unfortunately)..

dukenukemx

King lead? This the top of the rotor or bottom of the cap?

C531XHO

Sorry by king lead I meant the single lead from the col to the distributor cap. Enters the cap at the 6 O'Clock position. I only saw the broken end in my cap as I was lying on the ground trying to refit the engine lifting eye behind the [UK] driver side cam gear housing

dukenukemx

Just went to move my 928 onto ramps to replace the power steering belt and it died. Took my jumper wires to my fuel pump and I can hear the fuel pump is seized. It makes a very familiar thunk noise when I energize it. Would explain the event of it misfiring. This isn't my first fuel pump but the first one probably failed because the gas from the tank was brown and probably full of water. The car did sit for 15 years. Pretty sure I got this fuel pump from RockAuto. Can anyone recommend me a brand fuel pump that won't break the bank? It's funny because I just change the pump to my uncle's 1990 Mercedes 300e and it looks the same.

Speedtoys

"Can anyone recommend me a brand fuel pump that won't break the bank? "


Well, what did getting one rom Rock Auto tell you?

dukenukemx

The cheapest one. I'm going to remove it today and see what brand I put on.

copperstew

The fuel pump can fail by ingesting plastic from a decomposed fuel strainer. After 20 years they come apart.

If you haven't already done so, remove the tank and flush out all the old polymerized gasoline which probably looks like rose-colored sand particles.

Take out the plastic strainer and replace it with a new one. There are some tricks to that. Look it up.

If you don't, you will be replacing the pump again once it has ingested more sand and/or broken plastic from the strainer.

The Forgotten On

Get the Bosch part number and go hunting. It's best to order from our suppliers but sometimes they don't have the part on hand.

In that case, here is one in stock for $137 that will work https://www.autohausaz.com/pn/69471

dukenukemx

I did this a few years ago, but I didn't remove the tank I just disconnected the line going to the pump and let the old gas drain out. It looked really bad. I'm thinking it may have to do with the original fuel sender rotting away in the tank. I had since replaced it, but who knows what crap is sitting in the tank. I was thinking of putting a filter before the pump to catch any debris that might be in the tank. You might be right about the fuel pump catching crap and getting stuck.

Already got it and put it in the car. I did drive it yesterday and it ran just fine, until I shut it off and came back 10 minutes later and it drives with a misfire. This time shutting it off and turning it on immediately didn't resolve the problem. I took advantage of it and tried disconnecting each coil to see how the car ran. I disconnected the drivers side coil and I couldn't get the car started. Disconnecting the passenger side coil and the car ran, but obviously missing 4 cylinders. I did disconnect each wire from the distributor and it ran worse until I plugged each one back in. So today I removed the coil and the cap with rotor to see the condition. I don't think the cap and rotor look bad but I'm not certain how they should look. Maybe someone here can tell me the condition of the cap and rotor. The coil looks awful but that's because it's dirty. Not sure how to test it to see if it's delivering enough voltage. I did remove each wire from the distributor and it certainly made a visible spark. There's always a possibility of this being a fuel injector issue or fuel pressure. I replaced the injectors with ones for Ford with the 4 pin hole spray, but I hear a lot of fuel injectors failing due to the supply shortage issue. So it could be they aren't spraying enough when hot and then shutting off the car to cool it will get them sticky. Chinese junk. I'm thinking I need a method to see fuel pressure when this happens again, but that probably won't tell me if it's the fuel injectors.

I do still have the original injectors but they would also get stuck, but I've made no attempt to clean them. I guess for now I need a way to test the coil and the fuel pressure, as I don't have any tool that'll hook up to the 928's fuel rail. I'll also test the continuity of the cap and rotor as to me they look good, but then again I don't know.

copperstew

That cap is older than most college students. Time for a tune up.

Test the coil by verifying a spark at 12mm of air gap using a gap tester (a simple $15 tool).

Check resistance on the coil pins. They are numbered #1, #15 and the high tension pin is #4. There should be almost no resistance between pin #1 and #15 the small ones. Pin #1 to the high tension pin (#4) on mine was 9.75k Ohm. Check the Workshop Manual for your expected values (Section 28).

dukenukemx

I tried using this video for a 944 to see if my 928's coil at least checks out fine with a meter. It's about .5 ohms between the positive and negative terminals. The negative and spark output tested at 6,000 ohms. The coil is good, but this problem appears after driving for a while and left to cool a little. Hard to tell unless something fails all together. Gonna have to find a way to hook up my fuel pressure tester with the 928.

dukenukemx

I think copperstew might have something with the cap and rotor. I did some resistance testing on them and found the cap to be just fine, with the worst thing being the center carbon button going to the coil to have 10 ohms. Should be as close to zero but that's not bad. The rotor though has 738 ohms going from the carbon point section to the spark giver. I don't know their technical names, so I'm making them up as I go along. Not sure if the rotor has a built in resistor and how much resistance it should have. Anyone know if the rotors should have any resistance? Also if I decide to replace the coil, what coil could I use, cause there's a lot of choices apparently? Still haven't done the fuel pressure test yet.

**EDIT**
I think it's 1k ohm. Guess the rotor is fine?
https://jenniskens.livedsl.nl/Techni...2/MyTip283.htm
https://www.9xxteile.com/en/rotor-fo...300-1234332386