Misfire codes, low compression in #4

Its sad to see a lot of threads on blown motors and new short blocks but I'm learning a lot in the process. Trying to figure out the health of my engine in my 09 OBXT with 78,000 mi and looking for advice. Here's the rundown:

 

Started getting misfire codes at 75K (always #4 first than others follow)

Just got a compression test at a tuner and found:

#1: 140 psi

#2: 140 psi

#3: 138 psi

#4: 130 psi

 

I've been running OTS Cobb Stage 2 since 25,000 mi with a CNT catted downpipe and Perrin drop-in oiled foam filter.

 

Shop said I was running lean and could use a tune for safety/smoothness but did not recommend tuning for power with low compression and misfire in #4.

 

So far I have swapped injectors, coil packs, and plugs to rule out those items, cleaned the MAF, checked for air leaks.

I am installing a DW65C kit today to rule out clogged fuel filter or fueling issue.

 

Question is: Should I trust my engine or pull it and see what is causing the low compression in #4? If just a burnt valve, how much to fix? I would like to have a solid Stage 2 DD car at the end of all this.

 

Thanks in advance.

A leakdown test can be done with the engine in the car, it is a little more accurate as to what is causing your low compression in cylinder 4 (I.E. A burned/bent/damaged valve, or bad piston ring land). At that point you would be able to make a decision as to whether you will need to pull the motor out. My guess is you will have piston ringland damage to the piston itself.

130psi is not necessarily considered low compression. If your tuner implied it was, I would find a new tuner...

 

Running lean is VERY bad - depending on how lean. OTS tunes are a joke - get a real tune before something bad happens.

 

As far as the misfire - move the plugs and coils together and see if the misfire moves.

AMile- Thanks, I have thought about the leakdown test for a more accurate diag. Just trying to figure out if a 10 psi difference is enough to worry about.

 

gto7419- that leads to your question. The tuner did not say that 130 was low, as in, a fully blown motor, but did indicate it was the start of a problem and would caution me to push its limits. Agreed- I am worried the OTS tune has done some damage that a new tune wont fix by itself.

After swap the plugs and coils on that side, let us know if the code follows.

After swap the plugs and coils on that side, let us know if the code follows.

 

Max- I was hoping you would chime in I read through your build thread as well. I have already swapped plugs, coilpacks, and injectors from#2 to#4 and code did not follow. First misfire code to pop up remains in #4, pointing to an internal issue (?), though I have no idea whether a 10 psi compression difference should be causing a misfire.

Unfortunately, there's not much else to check. There's the remote possibility of leaking intake oring gasket. Time for leakdown..

 

Also, when does it misfire? At IDLE+COLD or IDLE+WARM or some other conditions?

xt2005- Misfire appears to happen at idle. It smooths out once you give it gas.

Idle is rough. I replaced the fuel pump today with the DW65c and CEL came right back on. I guess a leakdown is in the cards but looking more and more like the engine has to come out anyway.

xt2005- Misfire appears to happen at idle. It smooths out once you give it gas.

Idle is rough. I replaced the fuel pump today with the DW65c and CEL came right back on. I guess a leakdown is in the cards but looking more and more like the engine has to come out anyway.

 

Yeah that sucks. But does it show up at warm or cold or both idle conditions?

10psi difference is not much to worry about on its own. It's leakdown time.

xt2005- It's both warm and cold. Started over the winter and still occurring.

 

Max- Can you recommend a shop north of Hartford for the leakdown?

 

Thanks everyone for the advice.

Yeah. I guess it is leakdown time then.

Hometown, Yes, Call 860 749 7899 ask for Rich. He owns Colonial Tire & Brake in Somersville right on rt190 and the end of rt186. He does everything I don't want to do to my cars and my Dad's cars back in the 1980's.

 

He's also right up the street from the best auto machine shop in CT.

 

You can tell Rich, Byron sent you to him.

Thanks! I'm headed up that way this afternoon and might stop by.

subscribed for the results

subscribed for the results

 

same here.....

sub'd for similar problem (here)

He has an appointment for tomorrow. They will do a leak down test then.

I just heard from the shop that did a leakdown test today. I have a damaged/burnt exhaust valve in cyl #4. #4 was put at TDC (all valves closed) and compressed air was added through the sparkplug hole up to 80-90 psi or so. Air was heard coming out the tail pipe. They are confident it is not a ringland issue. Oil was put in the cylinder and the test repeated with the same results.

They are putting a quote together for me for removal of the heads (short block stays in. Didn't know that was possible), the machine shop charge, and reassembly.

 

Looking for input on anything else to ask them to do or check. Is there anything different I would want to do regarding the valve job for a mild stage 2 car? Are used heads an option and/or a good idea? Other advice?

 

Thanks for the interest. I hope that this thread can help others as this forum has helped me countless times.

Never mind the PM I sent you.

 

What are your long term plans for the car ?

 

Rich may find in his research that's its easier to pull the engine.

 

 

Oh I see the car has 78,000 miles. Get both heads rebuilt, get the car off the OEM MAP, give Mike Kinsman a call and meet up with him for a street tune. http://www.tuningalliance.com

Thanks Byron. Long term, I would like a reliable stage 2 DD. Very unlikely that I'll go beyond the parts I have now. Going the bullet proof TMIC route.

With 78,000 mi the shop is going to give me an estimate for the timing belt/water pump.

Can this wait or should I just do it now while the engine is out? If its a job I can do later on myself with the engine in I may wait to save some labor cost now.

The timing belt will have to come off anyway. So might as well put a new one on. Don't forget to change the pulleys and tensioner as well.

Yep, what he said, I thought about adding that to my last post but I had already turned of the computer.

 

A new oil return hose from the turbo is a good idea too.

 

You can read my click here link to see what's involved in pulling the engine.

Does anyone know of a discount code for rallysportdirect? I have a large parts list and want to get the best deal. They did not have a 10% off for Memorial Day as I was hoping for.

Did you look at fredbeansparts?