I recently purchased a tl type s with 158,000 miles. Everything on the car is great except the fact that the check engine light is on. We got the codes and realized that cylinder 4 and 5 are misfiring. One would assume that this could be caused by a simple non functioning plug or coil but no. After further evaluation we determined that it is not plugs, coils, or egr ports. The plugs on 4 and 5 both become fouled within 30 min of being installed. 2 shops have told us that it is most likely a piston or ring. I just need a second opinion because I have talked to someone that has had a similar issue which ended up being a flooded ecu. I don't want to end up pulling apart an engine if there is a much simpler solution. Important details: the upper intake manifold has been opened and had ports cleaned and is missing a gasket, the head has been opened in the past by someone and resealed with red silicone, coil on 4 is aftermarket and has been changed, all plugs have been replaced and coils have been switched, slight tick from misfiring.
If anyone has had this same issue or has useful knowledge and could help me out that would be great. Thanks.

 

Take the car to another reputable indi shop and have a 2nd opinion, sound like you bought a car that heavily molested.

 

OEM coil or an aftermarket one? There appears to be some very inexpensive coils floating around on ebay that could be garbage given the pricing.

 

Hondas/Acuras can be a little misleading when it comes to misfires. Some times one misfiring cylinder can give false misfires in other cylinders and P0300. Since cylinder #4 and #5 are right in front and 2 shops have told you bad rings, I would check compression first.

Some tools that would be useful:

• Do you have access to a bi-directional scan tool?
• Do you have access to a scope?

Some questions for you:

1. Is the check engine light blinking?
2. Is the car overheating?
3. Any noticeable coolant loss?

Some checks to perform:

Compression test: Get a hold of a compression tester and check cylinder #4, #5, and #6. If both #4 and/or #5 are lower than #6, then you have a compression issue. Then you can add a little motor oil to the suspect cylinder and re-check compression. If compression improves, then you probably have bad rings. You can use a leak-down tester to confirm.

Coolant pressure test: Get a hold of a radiator pressure tester so you can see if you have a blown head gasket. Put 15-20 PSI on the coolant system and wait. The pressure should not drop. If it does, then you have a leak and you'll need to see if it's going into your cylinders.

Ignition waveform: Using a scope and a low amp current probe, Scope the B+ to the coils before the splice point on the BLK/WHT wire using the current probe. Easiest would be to use a fuse buddy at No. 2 fuse underdash fuse box. Trigger off any cylinder to identify cylinders. Note if there any missing waveforms or just any one that does not belong. If the cylinder #4 and/or #5 are missing or firing too much, then you'll need to look at the control signal from the PCM. if the signal is missing or over-firing then you'll need to replace PCM.

Fuel injectors: Similar to the Ignition waveform. Scope the B+ to the injectors before the splice point on the YEL/BLK wire the current probe. Again, easiest would be to use a fuse buddy at the No. 8 fuse in the underhood fuse box. Again, note which is missing, odd, etc. If the waveform is missing then you'll need to see if the PCM is sending the firing signal. If the waveform is different than the others, you probably have a bad injector. A bi-directional scan tool will have a functional test to activate each individual injector. You can also use that feature to see fuel pressure drop for each injector.

 

Look at your cyl 5 and see if there's a helicoil or timesert where the plug threads in. If yes, the previous owner probably blew the plug out and had it repaired. There could be internal damage.

Check your ECM, its behind the radio in the center console. Pull back the carpet! It can get wet from the A/C system backing up onto it if the drain line is clogged.

Compression check and leakdown will help identify any issues with valves or rings. That red silicone that was used needs to be removed....

 

Just an update, we ended up pulling the front head and one of the exhaust valves on cylinder 4 was really messed up and not forming a proper seal. I don't really have any idea what caused it but everything else looked good. We took the head to a machine shop, put everything back together, and now everything runs great with no check engine light or misfires. Thanks for the opinions and the help.

 

Looks like a basic compression test or leak down test should have caught that. Did they do those tests?

Did you see any valve marks on cylinder 4 piston?

 

we did a compression test and then pulled the head off. The exhaust valve was deteriorated and had left some marks on the piston in cylinder 4.