tkloehn

I just bought a 2000 manual coupe with under 40k on it (only been driven 1000 miles in the last 8 years the guy before me had it.) Of course on the way home CEL went on. Anytime I am above 4000 rpm the engine doesn't seem like its running right and at 5000 rpm the CEL starts flashing. Ran the codes and got multiple misfires in 1 and 4. Got new OEM beru spark plugs and switched the coils from 1 and 4 to 3 and 6.

Took it out after and still had the same issue so ran the codes again, 1,2,4 and 5 are misfiring, still only above 5000 rpms. So its not the coils or the plugs. Sometimes it will be 1 and 4 other times 1,4,2 and 5
It runs perfectly fine under 4000 rpms but once you get up past there it doesn't have as much power.

Since it is both banks, both cats aren't likely to go at the same time so ruling that out. Next thought is fuel. I ran seafoam through the gas, but no results. Since it hasn't been driven and is both banks and seems to be limited to the last cylinders, my guess is not enough fuel pressure to supply all cylinders and just not getting enough gas to the last cylinders, although I'm not throwing any other codes(either weak fuel pump, injectors or fuel filter?)


Next step is to test fuel pressure. Anyone else ever have this happen or have any suggestions?

ZX9RCAM

NVM

Re-read OP.

tkloehn

Switched coil packs around yesterday (1 and 4 were misfiring so switched 1 and 4 with 3 and 6 which weren't) 1 and 4 were still misfiring and 3 and 6 weren't so ruled the coil packs out

996AE

Bad injectors? Seafoam and fresh gas.

tkloehn

I was thinking that as well since it has obviously sat for a while. Did run a half of bottle of seafoam through with a half tank of fresh gas. Filled up again with fresh gas and still misfiring. May throw another batch in or pull the injectors and clean them

kromdom

was a PPI or test drive done before you drove the car home? NTL, best of luck sorting your car out.

P.S. Just a WAG: dirty MAF?

Ahsai

Fuel pressure and flow rate. Fuel filter, MAF and Durametric.

tkloehn

kromdom, after looking at rennlist that was my first mistake. It was the first car I've bought, saw the miles, jumped too quickly and now I've learned the hard way but lesson learned for my next porsche. Took a test drive but never took it over 5k.


Ordering a durametric soon but in the meantime planning on cleaning MAF tonight and checking fuel pressure. MAF should affect all cylinders though and I haven't seen 3 and 6 misfire yet

Imo000

Wait until you can scan it and ONLY then start cleaning things. You can introduce another problem and then you'll be chasing your tail forever. Next time take the car up to redline during the test drive.

Macster

1000 miles in the last 8 years... Well, you have eliminated stale gasoline.

However, I'm not sure the fuel filer and fuel lines and injectors escaped some varnish forming in them.

BTW, I'd be tempted to replace the coils just to have the plugs and coils new. But the coils are probably not the problem.

Short of replacing the fuel filter (and possibly the pump), the fuel lines and injectors, about all I can recommend would be to use Techron. Use a bottle according to directions and then if you notice an improvement use another bottle. Be sure to change the oil/filter after you run the last of the fuel with the Techron added out of the tank.

You can check fuel pressure and delivery. Be aware the brass cap that seals the fuel line test point is not reusable. If you remove the cap you must replace it with a new one.

Before you dive into the fuel pressure/delivery thing though be sure you give the car and the engine compartment a good going over for mice sign. A car that has been visited by mice (or rats) can manifest all kinds of engine and electrical problems.

tkloehn

Finally got my durametric last week! In the meantime I cleaned out all of the fuel injectors. That brought it down to only cylinder 1 misfiring. Logging the data on the durametric, it was showing mostly high rpm misfires in cylinder 1 but several low end as well depending on rpm. Cylinder roughness was also higher on this cylinder (10 vs -3). Pulled the spark plugs again and saw oil on the diode of cylinder 1. Decided to do a compression test on all cylinders to rule out bad cylinder. Got good compression within 10 percent on every cylinder. With that, my guess is bad valve seal most likely. Looks like the engine will be coming down soon. I was planning on dropping the transmission anyways to do IMS/RMS so not a ton more work. Still winter for a while here in Wisconsin so I have nothing but time.
Any other suggestions before I drop the engine?

Macster

It is not clear the engine needs to be dropped or even opened up.

I didn't read the thread again but are the coils and plugs new? Before I dropped the engine I'd throw new coils/plugs at the behavior.

Are you sure the electrical connector/connection of the coil to the plug and the coil to the wiring harness is good?

Unlikely a valve seal is the source of the misfiring. If the seal was leaking bad enough to cause misfires I think you'd see the engine smoke at times.

I am not a fan of Seafoam. I am a fan of Techron. My advice would be - after you are sure the coil is good and the plug is good and the coil is connected properly -- would be to use a bottle of Techron as per instructions on the bottle. The SOP is you notice an improviement use another bottle. After you run the tank level down to say a quarter of a tank or so change the oil and filter.

I am thinking engine deposits or fuel injector deposits are causing the misfires. At 40K miles I suspect the engine never got run much above 3 or 4K RPMs and probably is pretty loaded with deposits. That it sat for a while unused didn't help.

You are sure the car is free of any rodent damage? You are running a top tier fuel and the proper octane grade and buying fuel from a busy station? Have you replace the fuel filer?

Triple Black

Are the cats original? If so, I would check them before dropping the engine.

Flat6 Innovations

Change the MAF. Don't just clean it, replace it.

tkloehn

This is what the plugs look like(maybe 30 minutes of run time on them) cylinder 1 vs 2




Macster, plugs are new, coils are not, but I checked for any visible cracks as well as switched coils around this weekend and no change in misfires. I believe the electrical connection is good as it runs with no misfires at midrange rpm and most of the time at idle. I will have to look into this however to make sure there not just a bad electrical connection before the coil. As far as fuel goes, it was filled up with the correct octane gas. Filter has not been replaced yet, but is on its way. I have switched fuel injectors 1 and 2 as well and no switch in misfires there. Durametric only has a single recorded stage 2 overrev so I don't think it was taken up very often. I don't remember the stage ones but it wasn't extremely high either. When removing the fuel injectors I looked over many of the lines and didn't see any rodent damage. I'll have to drain the seafoam filled oil and put some new stuff in with techron and see how it affects it


Triple Black, cats are original. How would you go about testing these? Should the entire bank be misfiring with a bad cat?

Flat 6, an MAF failing should cause most if not all cylinders to misfire if this was what was failing, correct? I'll check the MAF tonight on the durametric.