Driving on the freeway up a slight hill in sixth gear about 2800rpm and suddenly the engine starts running rough. Pull over and feels like it's running on 3 cylinders and chucking misfires for cylinder four. It barely gets above 3500 rpm and runs like I have a huge V8 under the bonnet!!

Find the MSD coil pack is coroded and not producing spark so I replace it with a new one and the BKR7EIX spark plug on cylinder 4. Still getting misfire on cylinder 4 and running horrible.

It starts and runs exactly the same with the spark lead disconnected of cylinder 4 so I know it's the only one.

Because I am pretty modified with RMW injectors I decide to swap the Injector and the pig tail connection from Cylinder 4 to cylinder 3 to see if it makes a difference. It didn't :(

So what next? I'm doing a compression test tomorrow hopefully when I get my friends tool. But is there anything else im missing and should be checking?

mod list bellow
RMW 450 cc injection
RMW street Cam
17% pulley
RMW Shorty Header
RMW remote tune
HFS 2 Water meth system

all help appreciated!!!!!

 

How do you know the misfire is cylinder 4?

 

Dollar bill test will tell you real quick if you have a burnt valve.

 

I see nowhere did you verify or replace the #4 spark plug wire. You said MSD coil pack was not producing spark, which is a path to pursue. You replaced the coil pack that didn't produce spark with a new one and yet the misfire persist. That is your strongest clue.

Not enough details you provided for me to comment if you have a burnt valve, or possibility of anything else.

 

I would add that just because the fault reported is #4 misfire. There had been countless cases that the problem rested with other cylinder. I recommend you verify ignition and fuel delivery to all cylinders.

 

This is pretty much what I was getting at, I just didn't feel the need to type it all out. Diagnostics are limited at this point based on OP post.

 

I've got similar mods and had almost the same problem earlier this year but with cylinder 1. Stock coil pack was fine and wires were less than a year old.

Zero compression on cylinder 1 and it turned out to be a melted piston when I pulled the head. Hopefully you have better luck.

 

Hmmm! Would you please share with us what leading up to your melted piston? What mileage did you accumulated after the engine mods, and any specific points of interest such as how hard you drive?

 

Hi all!

thanks for the replies Apprciate the input!!

So I confirmed the coil was bad as there was no spark. Replaced it and the spark plug it now produces spark with the plug removed so I know it's producing spark.

Code reads misfire cylinder 4. And when I remove the wire off the plug on that clylinder it runs the same. All the others won't start or die pretty quick after plug wire removed. Where as plug 4 makes no difference. And I know it's getting spark!! Or have I missed something there?

i also changed around the injectors and injector wire plugs. From cylinder 4 to cylinder 3 and the fault still persisted in cylinder 4. There was wetness on the spark plug when removed around the threads so I figure it's getting fuel.

i really hope it's not a melted piston.... Anyhing else I can do to troubleshoot?? Compression test today.

just to recap it happened under low load on the highway, not smashing it.

 

OK. That is now patently clear now with the additional details you just provided which are crucial but were absent. I think compression test should tell you something.

 

I would have preferred a burnt valve or broken valve spring over a melted piston.

While the cylinder wall on mine looks like I could have gotten by with just a hone and new piston/rings, I decided to get a used engine and swap the block myself. Would have been much easier to only swap a head but on the plus side I get to do some other maintenance while the engine's out.

My car's an '06 Dinan MCS I bought used 5 years ago already with all the Dinan engine mods plus RMW street cam & tune and JCW injectors. It's been pretty reliable with only the intermittent stalling on cold start which clears on restart.

Twice in the past year, months apart, I've had the car go into limp mode with code P0301 misfire on the highway, each time was during sustained full throttle pulls going uphill and each time the car would be fine after a restart. Then the third time this spring, the car did not clear after the restart and that's when I started digging in.

I suspect swapping the Dinan pulley for a 17% earlier this year without a re-tune did not help though I didn't think the engine would be that sensitive. Given the couple times the issue came up prior to the pulley swap I suspect the piston had been starting to go for a while.

 

WoW ! Interesting read on your rebuild issues!

i myself if I get low compression am hoping for a head rebuild rather than the block. I don't think I can stomach a rebuild. Too many things going on!

interesting like you with all my mods have had a stumble every now and again at idle. Thinking it was just the cam.

I am tuned for my mods but i also run water injection. I run straight water for temps down under in Australia. Again not tuned for the water, just as a safety net.

But I wasn't thrashing it when it went and as such no water was being injected at the time.

will the wet and dry compression test tell me if its valves or rings. I can borroscope the piston face if needed. I can also provide a leakdown if nescesary.

 

LOL. Not just you two have similar mods, similar symptoms, but exact number of posts - 30.

 

Haha! So sad. Will update with compression test results...

 

Thanks for sharing. Leave one wonder if the melted piston was caused by sustained detonation. Could the tune be too aggressive with ignition timing advance?

 

So compression test was weird
I couldn't do it warm because I didn't want to run it on three cylinders for five minutes so I did it cold.

CYL 1 - 120 psi cold
CYL 2 - 120 psi Cold
CYL 3 - 130 Psi cold
CYL 4 - 0 psi. Nothing not even a register on the gauge!

When I added a teaspoon and a half of oil to cylinder 4 there was still no compression. Again the gauge didn't even bounce.

sooo I think it's pointing to a doozy of a valve failure?? I can do a leakdown test but I guess I have to pull the head anyway...

i thought it would at least register something

 

I don't know that I would call a burnt valve a doozy of a failure but it could be a cracked head up by the plug entry point. Any milkshake in the oil?

 

Thanks for the update. ~120 seems a bit low for other cylinders, though it depends on the gauge and battery condition somewhat. What mileage has the car?

Next to no compression is very consistent with burnt valve with a small pie slice missing.

 

Hmmm...I was gonna go with a Dominator Cam and 450 injectors next spring...now I'm wondering.

Did you do a compression test before you added your mods? Jan told me to check to make sure my engine was healthy before I start to modify anything on the engine.

~Mitch

 

Yeah mine has always been around the 130 psi doing a compression test. Always run very well and strong.

battery could have been a touch low. Haven't checked the dipstick yet so I'll check that today for milkyness

Im going to pull the valve cover off to see if I can find any broken springs. That's my best hope!

If not I will pull the head.

The car could have been misfiring for some time due to the coil, having the RMW header on it after a while causes it to throw the too rich bank 2 code. So the misfire could have been hiding behind there for some time in between resets.

It has always idled rough after the tune and cam went in. Cold idle it would stumble until it was hot.

 

Broken intake spring!!! Thanks god the head doesn't have to come off

For anyone who's engine suddenly has zero compression when your not hammering it. It pays off to check the springs prior to removing the head to save a head gasket and time etc...

Spring can be replaced on the vehicle.

 

That is good news. Please keep us updated on your progress. In retrospect my remark of 120 psi compression test does not take into account a more aggressive cam with added overlap. I have no idea what is normal with this cam.

 

Ok interesting, yes it's RMW street cam which is more aggressive. I always thought I had a burnt valve due to my rough idle when cold but I was assured by Jan this was due ro the cam and tune.

Also all I did was undo the fuel pump fuse for the compression test.

1) is there anything else I need to do to get an accurate reading?

2) what effect does cold vs hot have on Compression readings?

 

Just a bit of negative thought, which I refrained from mentioning in previous post. As these valves are interfering I just hope the one with the broken spring is not bent. It is hard to logic if the broken spring was able to keep the valve from dropping too low for the piston to smash it. I incline to think not but it depends on the millisecond when it break. After it break I think the limp spring is likely to keep it retracted enough. You will soon find out when you inject compressed air to replace the spring. If you cannot get it to hold the valve close you know...

While you are at it I would replace all the valve stem seals unless you have very low mileage.

For me compression test is only a rough indication. A leakdown test is more suited for assessing the health of the piston, rings, and cylinder. On hot vs cold, it is hard to apply logic when you get higher reading.

 

Thanks, yes I think the whole interference engine vs non interference engine is hard to find a definite answer on.

When I pushed on the spring it was still tight enough to keep the valve higher than full downward stroke by far. So fingers crossed no problems there.

i think if I replace the spring with air like you said, I will soon enough know and won't really lose a lot of time if I have bent a valve.