The V8 Owners Forum -

Hi guys, I’ve just bought an Infrared Thermometer which I’ve used for measuring the temperature of the exhaust headers. I’m rather concerned on the results, I’ve got stainless steel tubular manifolds and I’ve measured each exhaust 3” from the cylinder heads the results are as follows.
No.1 436 degrees
No.2 422 degrees
No.3 350 degrees
No.4 436 degrees
No.5 415 degrees
No.6 396 degrees
No.7 108 degrees
No.8 360 degrees
As you can see No.7 is vastly different from the rest. First I thought No.7 had a faulty lead changed it no difference, changed the spark plug which seemed a lot cleaner than the other one I swapped out of No.2 still no difference. Anyone have any ideas on what is going on?

I would take rocker cover off and have a look at the valve gear, something could be wrong to stop the valves opening and closing when they should

Ian

Does it make any difference if you run the engine with that plug lead disconnected?

Engine ? Nature of fuel/induction ?

Such a low reading assuming test is done same and pipe/material/surface etc is all comparable to the others would definitely be a concern..

Plus you indicate that plug is also a different colour.

Cooling water in the chamber ?

DaveEFI wrote: ↑

Tue Mar 20, 2018 8:48 am

Does it make any difference if you run the engine with that plug lead disconnected?

Hi dave, just tried it and it made no difference at all.

paulsv8manta wrote: ↑

Tue Mar 20, 2018 8:40 pm

DaveEFI wrote: ↑

Tue Mar 20, 2018 8:48 am

Does it make any difference if you run the engine with that plug lead disconnected?

Hi dave, just tried it and it made no difference at all.

Dave had a good idea when he suggested pulling the plug lead, as it made no difference to the running of the engine it is safe to assume that the cylinder is not doing anything. It could be a valve train issue or an injector issue. You could pull the rocker cover off and turn the engine over by hand in order to see if the valves are operating correctly. I know nothing about injectors but there must be some sort of test that you can do on them. (assuming that we are talking about an EFI engine!)

A compression test and/or a leak down test on that cylinder would also be a good idea.

Pulling the spark plug out and earthing it out while cranking the engine will soon tell you if there is a spark, the engine may well fire up on the other cylinders when doing the test but that's not a problem.

Hi Sidecar,
Yeah it's an efi, I have a horrible feeling it's a valve train issue as the vacuum gauge on the dash is reading a steady 10 InHg indicating late valve timing. Looks like I'll be striping the front down this weekend!

I've done a compression test and they are all within 1 - 2% across all cylinders. earthed the spark plug and there is a spark. The engine is running rich (plugs are black except for No.7) as I have had problems setting the timing as its way off the tdc marks.

I would not pay too much attention' to the 'useful' information that you get on some vac gauges such as 'late timing' has the vacuum that the engine pulls on tickover depends on several things, if you have a long duration cam fitted then that will reduce the vac at tickover. (Not saying that you have such a cam fitted though). If the ignition timing is retarded at tickover then the throttle will have to be open more in order to obtain the tickover RPM, this will reduce the vac at idle. If you have a valve train issue with all the cylinders then I think that you would have an issue with all the cylinders and I doubt that the engine would run, if you have a valve train issue with number 7 cylinder then your compression test would have been miles off for that cylinder.

I think that its an EFI issue with number 7 cylinder. Does the number 7 spark plug look wet or smell of fuel?

Hopefully someone that knows about EFI will come along and give you some suggestions on how to diagnose EFI. (I only know about 4 barrel carbs).

paulsv8manta wrote: ↑

Tue Mar 20, 2018 8:40 pm

DaveEFI wrote: ↑

Tue Mar 20, 2018 8:48 am

Does it make any difference if you run the engine with that plug lead disconnected?

Hi dave, just tried it and it made no difference at all.

Right. Before going mad, make sure there is a spark at that cylinder.

If Lucas injection, each bank of injectors have the same injector driver in the ECU. If flapper injection, first thing I'd do is clean the plug to the resistor pack. No resistor pack on hotwire. Unplug the injector and measure its resistance.

Hi guys, the plug is smelling of petrol, and I’ve gone over all my Instalation notes/photos and the arrows on the timing gears are in line. Wouldn’t think the chain has jumped as everything is new.

Tested my 2.0ltr 4 pot (cast iron exhaust) temp and that’s only 250 degrees across each port.
So I’m thinking the v8 which is running stainless is way too hot for a new engine!
I think I’ve made a huge mistake, noticed in my notes / check list I’ve forgotten to set the lash/ preload (plonker) and maybe No.7 is right and it’s all the others that are the problem?
I’ll be interested to see what you guys think.

Swap injector wires from the cylinder beside it to see if the problem moves.

If not, swap injector to cylinder beside it.

If the plug is soaked with fuel, bin it and replace.

You already say you've confirmed a good spark available to that cylinder ?

Thanks stevieturbo I’ll add that to my list of things to try.