curtsr

About 500 miles ago my 2003 C4S started misfiring at stop light idling occasionally- maybe every 50-75 miles and only at idle. The CEL would flash, increasing throttle speed would stop the flashing and would not turn the CEL on steady or post "workshop". If allowed to remain at idle during one of these events without increasing throttle the error code would become steady and need cleared via scan tool.

I assumed the #4 coil pack was degrading and put them on the "to do" list. A minor inconvenience; isolated to one cylinder and intermittent. Yesterday morning I was headed to work and noticed a little ticking noise on the passenger's side exhaust with the PSE on quiet and figured it was an exhaust plumbing issue. Switching the PSE on loud seemed to eliminate the issue- or at least drowned it out.

When I returned home in the afternoon and was parking the miss became a real one. The miss was very pronounced, increasing throttle would not smooth the miss and after clearing the code it would immediately throw it again.

Engine particulars: 6 speed car with 49,000 miles, IMS Solution installed Jan 2016 @ 36K miles, AOS replaced at that time. No smoke, no intermix, no liquid leakage, no oil consumption since last change, normal appearing plugs, Beru coils. I switched plugs and coils of cylinders 5 and 4 to see if the misfire would move and the misfire stayed at cylinder 4 per the scan tool.

Cold start this morning car ran smooth for about 40 seconds with no CEL lit but the very small perceptible miss was there. After 40 seconds the miss felt worse, the CEL started flashing and raising the idle would not prevent the flashing from becoming steady again.

Put your extra hour to good use, any ideas?

jllphan

Maybe i missed it, but did you can the CEL to see what code your getting? That would be step 1.

IF it's a misfire on one of the banks (IIRC it will be a CEL code in the P300 family: P0300 Misire detected, P0301 Misfire cylinder 1, PO302 Misfire clyinder 2 and so on...), replace the coils (and plugs if it's been a minute).

curtsr

Yup step one, why I put it in the title... and indicated that I swapped #4 & 5 spark items and noted "misfire stayed at cylinder 4 per the scan tool"

Ahsai

Based on the fact that the code stays at cyl #4 despite swapping both coils and plugs between #4 and #5, that sounds like a mechanical issue in cyl #4. The other less likely case is wiring issue.

Do you have a Durametric that you can monitor the misfire counters in real-time? Next step is probably a compression and leak down tests on cyl #4. Also a good idea to check the oil filter for debris (not that I expect some but it's safer that way if it's truly a mechanical issue).

Ahsai

So just P0304 or P0300 as well? Any other fault codes and what scanner was used?

curtsr

No Durametric, code P0304 only. What mechanical issue would not be present at start up then arise 40 seconds in. Lifter?

Scan tool was a wireless unit called ODBLink.

Thx!

Ahsai

I use OBDlink too. A great generic scanner.

If the intake valve lift is stuck to high at idle, the cyl will misfire. The first 40s the engine is likely still in the fuel enrichment stage (cold start) so maybe it's leas sensitive or more tolerant. Also, the CEL will be tripped only when the misfire counter exceeds a threshold within a number of ignitions window so that will naturally take some time especially if intermittent.

996AE

I had a similar issue with cyl 6.

Compression and leakdown numbers were good. Tested and replaced injector and ran two quarts ATF with fresh 0-40 Mobil One for 100 miles and re did oil filter and fresh oil.

All good 500 miles later.

I went through the same issues first replacing coil packs and plugs. 30k miles and ten years they were due anyway. That didnt change the occasional PO306.

Race shop that did my work said really rare to see a lifter issue on 996 motors. If not coil, plug its the injector 90% of the time.

Schnell Gelb

Curt mentions 'ticking'. It may be useful to poke around #4 with a stethoscope while the tick occurs ? Just to confirm the noise source is the cam cover, not the cylinder head or crankcase.
If you decide to replace #4 injector, I suggest you investigate the price for a complete set of the upgraded Bosch . The prices have dropped a lot. If one has failed, they've all done the sme miles/age so why not do all? I started off replacing one , then another failed. At that point I switched to generic Bosch+upgrade.
OBD link options:
http://scantoolcenter.com/blog/best-...ooth-scanners/

curtsr

Also a useful real time dashboard with speedo, RPM, O2 voltages, battery voltage, boost and more. I use it along with HLT when I HPDE my other car.

curtsr

Halfway through a tank of Seafoam and no issues. Looking like a dirty injector.

Schnell Gelb

If the ticking was caused by deposits on the injector(??) maybe Techron would help in future?

curtsr

I've used Techron probably twice in the 9K I've driven this fine car.

I get my gas exclusively at Costco (where I get that Techron) and I always believed that they sell pretty good gas with detergents added.

I'm not sure about the chemical differences between Seafoam and Techron- if one is more aggressive in breaking down carbon and deposits but I believe is is. I've not noted instructions on Techron for introducing it directly into the intake stream.

Mike Murphy

I was thinking injector about 1/2 way through this post. I’d guess Seafoam is a lot more potent (more detergent) than Techron. I’ve also used BG44K fuel treatment. Both those were during DE or track days, but I’ve yet to try Seafoam.

SeaBass8

Tell me more of this seafoam you speak of...
Okay yes I've heard of it but no experience at all using it. It cleans the internals? How much and how do you use it.

I like the idea of improved performance of cleaning the fuel system.