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. If anyone has any Ideas, I'm open to suggestions.

87 944 C

What do you mean spark jumps about 3/4 from plug 4? Like jumps from one wire to another?

Do u see any coolant loss?

Sounds like the injector is fine, was it a fully assembled engine or did you have to install the head? 165 might be low, but its still within 20 percent of your highest 185, on paper thats ok, but check cyl 4 piston.

Other than that, I can't see why the engine would be giving you issues

johntorg

No, If you put a screwdriver in the end of the plug wire with the engine running, it will jump about 3/4 inch to ground

johntorg

No fluid loss at all. Cylinder 4 seems to have compression, spark and fuel. The engine came as a spare when I bought my race car. It was supposed to be running well when it was removed for the Race engine. I just resealed a leaking upper balance shaft and installed new belts and rollers, and clutch. Engine had recent rod bearings.

johntorg

I will also pull the cam cover just in case its a broken valve spring. Perhaps the valve is sealing while cranking and hanging up while running? I grasping at straws here, Does anyone have some better ideas?

blown 944

I would try changing the DME temp sensor.

johntorg

How could that affect only one cylinder?

87 944 C

i'd say more of bad spring or something stuck in the valve spring rather than the valve getting stuck...maybe even a slightly bent valve.

if needed by friday, i'd swap the engine out again for the known good one. then rip the head off this one and rebuild it or let it sit in an engine degreaser of some sort to get any crap out of it.

even better queston, what's the fuel pressure at that injector? might not be the injector, could be a dirty line between 3/4 and not enough fuel is getting to cyl4.

if you break the engin down to sectons, air/spark/fuel/mechanical. you know you have air/spark. fuel injector sounds ok, but you don't know if enough fuel(or any) is injecting into the cylinder. mechanical would be the only other option, and that option would most likely be in the head itself.

and dme temp sensor would effect only 1 cyl

Eric_Oz_S2

All I can think off is

Ignition lead to cyl 4
Distributor cap
Injector
Valve spring?
Lifter?

f1rocks

Does the #4 exhaust get hot when you let it run for a bit?

If you're getting spark, getting fuel, you should be seeing heat there.

Have you checked the cam timing?

johntorg

Just changed the timing and balance shaft belts and they are in time. All wires and cap were changed after I discovered the problem. I'm still confused about the DME temp sensor affecting only one cylinder? Can anyone explain this? #4 exhaust is not as hot as the rest (I'm pretty sure, but will check again tomorrow).

johntorg

I also think it may be mechanical and will pull the cam cover, first thing tomorrow.

Triple_T

Bad spark plug?
Had a similar thing happen years ago... the insulator was faulty on the plug and spark wasn't getting thru to electrode.

johntorg

Already swapped twice

peanut

well the first suggestion I'd make is for you to resize your images forcrisakes
I have to scroll the whole thread back and forth horizontally to read it .

This is what I would suggest.

#1,2, &3 cylinders are functioning normally ok yes!?

Swop the fuel injector and spark lead from any of the first 3x cylinders with #4
This will at least prove the spark lead and the injector are ok .

If your injectors fire simultaneously (Motronic ) then swop #4 injector electrical connector for one of the other 3x and see if the problem shifts from #4 to the other cylinder

All you need is fuel ,air spark and compression to #4 cylinder for combustion so one of these are missing its that simple .

If you have fuel air and a spark it has to be lack of compression....one of your valves in #4 sticking or not seating properly or a hole in your piston /head gasket etc . Have you double checked your valve clearances ?