rich c4s

So the day started out great... finally a warm, bright day here in CT with no snow in sight... then P0300, P0310, P0302, P0303 multiple misfires, cylinder #1, #2, #3.

My '97 C4S has been sitting since mid January when the first of many snow storms rolled through. Started right up this morning and after warm up, went for a 15 mile drive. At the first stop light, it started running rough and may have even backfired. Time to return home. CEL came on and after a few miles started flashing. I was ~ 3 miles from home so tried to make it. The car had no torque, wouldn't go much over 2,000 or 2,300 rpm with no power. I mean I worried it wouldn't make it up a hill. At a stop light (1/2 mile from home) the car sputtered, coughed and turned off. I'm afraid I might have heard some clanging. It would not start. It cranked fine, but no 'spark'.

So... what i know is:
1. car has 1/4 tank of 2 month old gas. 78k miles
2. the fan, A/C, alternator belts look fine
3. after sitting in my garage for several hours (a flat bed got me home) I put in a new DME relay. It started right up, but CEL still flashing and throwing misfire codes P0300-303. Put old DME relay back in, same thing.... car started, CEL flashing and throwing misfire codes.
4. The points, caps, wires were replaced at the 60k service, but have 10 years and 20k miles on them.

So any thoughts on what to check next? Is there a way to check if the belt driving the secondary distributor is working? Is there a way to check the timing chain? Or do I go straight to new caps, points, wires?

Thanks everyone. I've run out of time on a Sunday, so I will have all week to do more research until next weekend.

Jwolf427

I would start out by flushing the old gas and fill up a fresh tank. Two month old gas can cause misfires.

Steve Weiner-Rennsport Systems

Rich,

The place to start here is to replace the ignition components; plugs, caps/rotors, and wires. Make sure the distributor drive belt isn't broken, too.

I would also check the fuel injectors on the left (1-2-3) side to make certain they are working properly.

Unless you stored the car with a full tank of fuel, you may have some water in the gas and that wreaks havoc with the FI system. This requires draining the tank and replacing with fresh stuff.

nine9six

EDIT
In thinking about the posted problem more; Steve's recommendation to check the 1-2-3 bank injectors is completely valid considering the stated codes, and probably a very valid first step to check.
As you may have gathered, I don't believe in throwing parts at a problem, just because they may be related. This is a sure fire method to empty ones wallet, needlessly.

Rich,
Steve provides a more complete list of possibilities, but...
Because replacing plugs and plug wires is far easier said than done, I would start as Jwolf previously indicated...Plus, you're gonna be north of a $500 parts replacement program in just the plugs, caps/rotors, and wires; on an, "if come."

If you weren't throwing misfire codes prior to winter storage, it would seem more logical to start at the possible fuel issue first, and work out from there.

p.s.
If any of these components listed above have been recently replaced, you might want to cross them off the list.

J.B.H.

I would follow the advice you have already received from the guys... For what its worth...
I had the exact same problem a couple years back.. Car came out of storage.. I washed the car while running it as I always do, careful not to spray water in the engine compartment (turbo decklid), no issue. Three days later I go out to the store to pick something up for my wife and get caught in a downpour ... have the same issue that you are experiencing. Turned out to be a hairline crack in one of the caps... I did not notice the crack on my initial inspection. Its only after opening it up and removing them did I see it. Btw, don't run the car hard to try and clear out the problem.. You could foul your cats as the car is running rich with the issue.

Mike J

Unlikely fuel in the tank if it's isolated to the same cylinders. Two months is not that old. Funny the misfires are on one side. If you are getting codes across all cylinders then I would look at changing the fuel out.

Do a visual check first, perhaps something decided to eat some wiring, etc?

Check for the distributor belt is pretty easy - but you will need to remove the lower ignition cap. If you do that, the rotor should not be free running but, with a bit of slop, be locked to the main distributor shaft.

That sort of loss of power is good in a twisted way since it's easier to find issues, those more subtle intermittent problems can be real bears to find.

When the car is cold, did it change the characteristic?

Anything else around the problem, was anything changed recently, or the car was running fine, you parked it, and two months later started it up again?

Cheers

Mike

knorrena

This sounds like a faulty hall sensor, a dirty hall sensor, or a hall sensor that has fallen out of alignment to me.

The hall sensor is like a crank shaft location sensor, but it reads off of the flywheel as I recall. It is used by your ecu to tell it when to fire a coil pack. Some procedures for testing it can be found here:

https://rennlist.com/forums/993-foru...op-manual.html

pp000830

I would do the caps and rotors if they are more than two years old and check the distributor belt even though they are unlikely your issue. Sometimes a crazy multiple cylinder misfire codes are caused by a vacuum leak where one of the little hoses has slipped off its nipple or one of the fittings has developed a crack or leak resulting in a mixture issue. The problem can come on suddenly. Just a quick check of the lines to the various Vario ram parts and other places on the engine is a good place to start. If your wires are bad or your plugs are fouled the problem would not come on suddenly so I would not go there. The Hall sensor idea resonates for me as a problem with it can be a sudden thing as well.

I once thought I had some bad gas so I took a sample to the place where I purchased it and they had it tested. I went to two different shops before a loose vacuum line was found.

Andy

BesideTheBox

You can't go wrong by checking all of the grounding points.
I had a very similar problem, reporting misfire on cylinder 6.
Tried lots of things, none of which fixed the problem.
Cleaning the grounding points fixed the misfires for me.

More information at this link: https://rennlist.com/forums/993-foru...l#post10388201

bruce7

Clean the MAF sensor with spray MAF sensor cleaner.

Use a scan tool to read the fuel trim numbers.

If the engine has a misfire with low fuel trim numbers, the problem
could be the ignition system or engine mechanical.

If the engine has a misfire with high fuel trim values, look at a
possible problem with the injectors.

Costs for the parts could run higher than the $500 suggested.
Ignition wire set - $530
Caps and rotors - $350
Plugs - ~ $50
Labor - free if you do it otherwise $125 per hour and up

nine9six

Whew!
Not sure where you shop, Bruce, but I found OEM Beru wire sets for $340, Bosch OEM caps n rotors $180, Bosch plugs $50. So as stated, the suggestion was at a price NORTH of $500.

In retrospect, I guess your price quote is indeed north of $500 as well, yes?

P.S. I like the suggestions of the hall sensor and grounding points; and while you're at it, you might also consider a failing DMF as the culprit, to go with that hall sensor, just in case the sensor is operating correctly.

rich c4s

Thank you Gentlemen!

So, I’m still scratching my head on why just all left side misfires? Coincidence or is it telling me something? Seems old fuel and distributor issues would be more random, than just the left side. Mike has an interesting thought, that the CEL light first came on and had the power loss after the engine got warm.
So here’s my plan, based on your insights, difficulty, logic and cost….knowing everything was fine in January and the car has been bullet proof for the last 15 years (only exception is a wobbly flywheel throwing codes and new clutch). So checking the DMF is a good suggestion, but I will put it lower on my list since it was replaced 25k miles ago.
1. Drain the fuel and fill the tank
2. Lift the car and look for critters feasting on the left side. Although everything looked fine from my inspection from the top… and no critter ‘evidence’ on the garage floor
3. Check vacuum hoses and ground points
4. Run the engine to get fuel trim measurements. What values indicate high / low?
5. Check cylinder head temperature (CHT) sensor controls the amount of extra fuel used during startup and warmup
6. Check & clean Mass Air Flow sensor. Making sure the clamp holding the MAF Sensor's pipe in is tight. Maybe a lean condition the result of a bad MAF sensor?
7. Check ISV valve, make sure it is clean. What is this?
8. Check fuel injectors. Any way to do this with my OBD reader? Otherwise, I'll start pulling the left side ones.
9. Check hall sensor
10. Pull the caps to check for hairline cracks and corroded contact points. Double check the connections to the two ignition modules - and refresh with dielectric grease
11. Change caps/rotors. Sunset Porsche cost for caps and rotors is ~$350. Pelican has Beru caps for half the sunset price. Is there a perspective on if beru is good to use? I don’t believe in just changing things out, but I was a little surprised that the caps, rotors and wires are all 10 years old. Even with only 20k miles on them. So at this point, age is an enemy. So at this point consider doing what is left of the full 90k service 10k early.
12. Change wires?
13. Change belts? (only use PORSCHE OEM belts to avoid misfires)
14. Check DMF. Check RPM readings on OBD. A failing flywheel can cause apparently non-sensible RPM readings. Also look for a failing DMF tricking the DME to make adjustments to A/F ratio


I'll attach OBD data once the new fuel is in.

Thanks again!!

rich c4s

So here's my update:
1. No evidence of critters.
2. Siphoned the fuel out of the sending unit hole and refilled with 15 gallons. No Change
3. Swapped coil leads. No Change
4. Installed new Bosch rotors and caps. No Change
5. Removed and Cleaned MAF sensor. No Change

Hopefully I can attach OBD II scan measurements. Unfortunately they are all Greek/Deutsche to me. Any insights here?

Next is leak down test. I am feeling no 'compression' from the left exhaust pipe while idling.













Top rotor and cap after 25k miles and 12 years





Top cap after 25k miles and 12 years





Bottom cap and rotor

nine9six

duplicate post

nine9six

Is that a big ol crack of approx 180 deg on the bottom cap at the coil wire center point? Contacts look to be burned or ozone deposits. Try a pencil eraser to remove deposits. If you can feel roughness or lip/step w/fingernail, it's burned and should be replaced.

Photo of the rotor should be of the leading edge of the copper contact, as well as from the top view, to capture condition of both contact points.

FWIW, I recently (last year) purchased Bosch caps n rotors. $85 ea. caps; $25 ea. rotors @ pelican. $350 is no bargain!

Could also be failing DMF depending on where the rubber center is failing first, and maybe why the misfires are relegated to cyl 1-3.