johntorg

I just finished installing a 100K mile S2 engine in my race car after my "Race" engine Hydrolocked and seized up. Number 4 cylinder is not firing most of the time. Sometime it seems to fire for the first 10 seconds or so after starting and the cuts out. I have tested the following:

Injectors all fire when cranking.
Identical clicking noise on injectors when running (stethoscope)
Spark jumps about 3/4 inch from #4 plug wire
Compression on #4 is a little low 165PSI vs 175 to 185 on the other cylinders.
Pulling off plug wire one at a time. #4 no difference Others reduced RPM
Spark Plugs 1-3 tan 4-Gray.

I have swapped the following:

DME
Spark plugs, wires, dist. cap and rotor.
I don't have any spare injectors so I haven't been able to change them.
I installed new FFR and Fuel Dampner
Tomorrow AM, I will swap #4 injector with another and see if the problem follows the injector.

I will try to swap out the igniter, just in case it is general ignition weakness showing up in the lowest compression cylinder.

I will be racing at Sebring on Friday and really need to find a solution. I do have another spare S2 engine in a street car, but really don't feel like doing another engine swap.

Below is a picture of the number 4 plug. I anyone has any Ideas, I'm open to suggestions.

dgmark

If you are shure that it is #4 cyl the first thing I would try is swapping that injector to another cyl and see if the problum moves. You have to start eliminating sources of the problum. It looks like compression is good. so thats one thing off the list. I dont want to speculate on anything else right now because you will be chasing your tail. Try swapping the Injector and post results.

rlm328

I would pull the injector wires one at a time vs pulling the injectors. Have you tried tapping the injectors with the end of a screw driver or something that is not heavy. How old is your injector harness, it could have a corroded wire. You said the wire will spark, does your plug spark sometimes the element inside can break. Have you done a leak down test to check your valves? Good luck chasing it down. You may want to post your question on the S2 or 944 turbo forums. Probably get a better response over there.

flatsics

I've run into that problem with 2 valve 944's before. On those it was a broken/chafed wire in the injector wire harness under the plastic cover on the fuel rail.

Chaos

+1 on checking the fuel rail,my S2 has had a couple fuel rail problems.
Stock chip?
Plug wire?
I once had my injectors balanced and one came back "off"

johntorg

I'm interested in what you found wrong with your fuel rail? The injector does spray with approximately the same volume of all the others, when cranking and when I put voltage on it manually. It could be a bad wire that opens up while running, but with a stethoscope, I can hear the same clicking pattern as all the others. It is difficult swapping the injector wires because they are not physically long enough to do so. I would have to make and extension to the wires, but I am pretty sure I don't have any male connectors to make them. I might try cutting and splicing wire extensions into the existing harness, but I hate to cut up what may be a perfectly good harness.

I have swapped all of the relevant ignition components and have pretty much ruled them out at this point.

Matt Romanowski

It needs air, spark, and fuel to run. You're saying it has all of those and compression, so there is something your missing.

Ernie J

First of all do not use the platinum spark plugs. do a leakdown test, bent intake valve might be the issue.leaking intake pushes the intake charge back into manifold , leans out fuel mixture, weak cylinder.

flatsics

Is the ignition order correct?
Cam timing?

Other than that it could be a bent valve.

Fast82930

I had a similar problem last year starting my 2v 944 racer to load in the trailer before my first event, #1 wasn’t firing. I suspected injector at first and ended up thrashing around for a few hours checking everything you have.

My final hail marry was putting in 4 new plugs… it fired right up and has been perfect since.

johntorg

I run on normal plugs, just swapped in the platinums for a test. I did double check the plug wiring sequence and cam timing. I checked the valve springs and they look OK (can't see them very well). Re: bent valve, it is a possibility, but I do have 165lbs while cranking.

Re: Missing something you're absolutely correct. Under cranking conditions everything is OK, problem is checking conditions with the engine running

ltusler

Under cranking might the cold start valve be adding enough fuel to get to fire?

Chaos

Rail had a slight leak only under high pressure. Brand new plugs arw a must!

johntorg

Problem Found It was a broken outer exhaust valve spring on the #4 cylinder (forward spring).

Thanks for all the help and suggestions.

johntorg

Problem was found by checking each valve spring with my finger, when the valve was closed. You really can't see much on a 16V. Now to see if I can change the valve spring without pulling the head. I can use compressed air to hold the valve closed, but I don't have the proper valve spring compressor. Does anyone have experience doing this?

If that fails, I have a spare head that I can install, that is actually fresher than the one on the engine.