I've got a 16v 4age engine running on Omex with GSXR T/B's and std injection. Problem I have is that No. 4 cylinder is not firing on tick-over, when the rev's build I think all is OK. I've had the head skimmed and valves re cut as compression was low on 3 cylinders but still problem persists. I've swapped over plug leads and it has made no difference.

So what should I look into next? Plugs? Injector? Any other ideas as to route cause would be most welcome????

Thanks in advance!!

Rich

I take it you have tried swapping the plugs around to check its not a plug on its way out? Are you still running with the distributor fitted? If so then check the dizzy cap.

I'm running without a dizzy and I've got a ford coil pack with trigger wheel.

Swapping of the plugs and the injector is my next job but think I've tried this before...hence posting to see if I've missed something obvious....or not so obvious....

try an injector. unplug it to see if you can hear a change.

Rob

Good idea about un plugging the injector!

I've now put in a new plug, re tested with different leads, tried swapping over the coil pack feed (No. 1 and No.4 fire in pairs the guy from Omex told me), swapped over the injectors and still it's only firing on the same 3 cylinders with No. 4 not firing.

So what can the problem be??

I'm getting F****G annoyed now....

Rich

Tight tappet? No 4 T/B out of balance? air leak on no4 inlet? Might be a good idea to do a compression test or better still a cylinder leakage test which would show up any valves/rings etc. If you have access to a compressor I have a cylinder leakage tester you can borrow but you would have to collect it . Could take it to work in Wimbish if you want.

Hi Rusty

I hope the head is all ok as I've just had the head skimmed and all the valve seats re-cut but aim to double check via a compression test. The T/B's were balanced when I have the engine RR set up a little while ago (also had the problem then too), so it is looking like it might be the bottom of the engine - just after I've had the bloody thing out too. And I don't think Ive got any leaks. So might take you up on the cylinder leakage tester in a week or so's time as I'm away this coming weekend (and I've got a compressor). How does it work?

Rich

If you set the engine to TDC on the cylinder to be tested , remove the spark plug and screw in an adaptor which is connected to the tester , connect to an air line and check for air leaking from the inlet, exhaust etc. . What plugs does the engine have so I can check to make sure I have the correct adaptor.

If you've checked the electrics sufficiently then other things to consider are the valve clearances as already mentioned, broken or possibly a weak valve spring (rare) and again as mentioned poor ring sealing on No 4.

My engine has a similar problem as it eventually lose spark on No 3. I can clean the plug and improve the spark but eventualy the spark plug will need replacing. I know my No 3 was close to its wear tolerance when I put it together so I'm assuming its burning oil and fouling the plug.

What compression reading should I expect to see? Would a low rreading lead to my problem?

Rich

Uneven figures are a better idication of a problem. So one cylinder being very different would be a sign of some sort of sealing issue. Very rough guide but I would say 165 - 185 for NA (20V engines at 10.5:1 would be at the upper end) and 145 for the SC engines.