Engine wont fire on one cylinder

Janz99 · Post by **Janz99** » Mon Aug 14, 2006 7:55 pm

Finally got the car up and running last weekend, and took it out for a ride last night. I got about 45 min worth of tuning in before it broke. Well it didnt really break, but here is my newest problem:

http://euter.ftux.com/IMG_4920.JPG

I thought mabey it was a leaking injector, but after the car is shut off, the fuel pressure stays pressurized for quite some time.

The car runs, but it is very noisy, runs very rough, back fires with any touch of the gas pedel.

As of right now i am running MS&S, here is the datalog of when it happened, and also my MSQ just in case you wanted to have a look at it. I am running a top feed rail with mustang #42 injectors set at 65 psi base FP.

Datalog:
http://euter.ftux.com/ryan69.xls

MSQ
http://euter.ftux.com/After%20car%20stopped.msq

Make sure you right click the link and save as.

Took the intake off today and this is what i find on the intake and the heads:

I also did a compression test, and this is what i get:

1=185
3=190
5=190

2=185
4=185
6=180

So i am getting decent compression, doesnt seem to be any bent valves, ive swapped the spark plugs, spark plug wires, injector connectors, and still i cannot get this cylinder to fire. The oil on the intake also scares me!!

If anyone has any idea's i am open to pretty much anything at this point!!

Thanks
Ryan

Janz99 · Post by **Janz99** » Mon Aug 14, 2006 7:57 pm

Forgot to mention what the car actually is.

1994 Mazda Mx-6
2.5L V6, completly built, forged internals

shaodome · Post by **shaodome** » Mon Aug 14, 2006 7:58 pm

This isn't so much a megasquirt issue..its a mechanical thing. This was posted here hoping some people experienced with engine building would have an idea what that noise might mean.

Please download the video. You can hear the popping that is coming out the intake. Is it possible to still have cylinder pressure and a burnt valve?

jsmcortina · Post by **jsmcortina** » Tue Aug 15, 2006 2:52 am

shaodome wrote: Is it possible to still have cylinder pressure and a burnt valve?

When I've bent valves I get no compression. A useful test device is an adapter that threads into the spark plug hole so you can do a poor-mans leakdown test and hear air blowing passed the valves.

James

Janz99 · Post by **Janz99** » Tue Aug 15, 2006 4:50 am

My brother has a leak down tester, but i wont be able to get it for another week or so. Its wierd because i can hear POPING in my intake piping, and air is coming OUT of the inlet of the compressor housing.

To me it seems like a valve issue, but it made good compression so i was leaning towards something else??

I made a video of the popping noise coming from the intake, i tried to upload it last night but it didnt work, ill try again today when im off work.

Ryan

shaodome · Post by **shaodome** » Tue Aug 15, 2006 11:21 am

HEre is the sound:

http://www.powersquirt.com/noise.wmv

PSIG · Post by **PSIG** » Tue Aug 15, 2006 10:29 pm

There are several possibilities here, starting with spark firing order and ending with a broken exhaust valve rocker. I've had both events and the effect can be similar. The broken exhaust rocker caused severe backfiring at slightly higher revs when the intake would open and the partially burned compressed fuel/air mix popped back into the intake.

It also did fine on compression test, and leakdown too, since that was done at TDC when the valves are closed anyway. Exciting stuff when you're leaning into the engine compartment doing a static break-in and it starts crackling flames like a nitro Top Fuel dragster out the top.

Anyway, I hope it's a simple thing!
David

Janz99 · Post by **Janz99** » Wed Aug 16, 2006 7:26 pm

I know the spark firing order was correct, i even played with a few plug wires to make sure it wasnt just a bad wire. I am starting to lean towards a valve that isnt seating properly, which really SUCKS.

Ryan

PSIG · Post by **PSIG** » Wed Aug 16, 2006 9:07 pm

The easiest way to confirm a poorly seating intake valve (besides a leakdown test or just pressurizing the cylinder like James said) is by reading your MAP gauge. A mechanical vacuum gauge is easiest to see trends in the cycle, but it's quick and you can even diagnose using a MS datalog. Websearch for engine vacuum diagnostic. Amazing what you can diagnose while saving $ and time doing it. Worth a shot I think.

David

allenvos · Post by **allenvos** » Thu Aug 17, 2006 6:21 am

Check and make sure the cam lobe is not wore off the exaust valve of that
particular cylinder.

Make sure that exaust valve is opening all the way.