1987 3.2 Carrera Backdate project - Sladeys hotrod

[sladey]

So fuel then. I know there is fuel in the fuel rail (would t start otherwise)

I removed the left hand fuel rail


Unlikely/impossible to be a block in these holes as they are so big, but I blew them through with an airline anyway (all clear, obvs) and then put it all back together.

The injector could be failing but this seems unlikely given that

- it’s a new injector (as they all are)
- It’s a new injector loom
- the symptoms are the same as before I replaced the injectors and loom (apart from slight increase in smoothness) - would seem remarkable that one of the old injectors wasn’t working and now one of the new ones is doing the same

[sladey]

Yes, put some fuel in it for sure (glad to have been of help)

Thanks mate. Good to know I’m in the hands of experts here.

[Bootsy]

Here all day if you need anything else

[Nine One One]

Swop the injectors over from one side to the other see if the temperatures rises now on the other bank?

A lean mixture can lead to lower Cylinder head temperature, but would not thought that much, it s almost as if that bank is not getting enough fuel to fire those cylinders properly.

Take it the air flow sensor plate is moving correctly, I think they can be adjusted?

[sladey]

Thanks - might leave that until tomorrow (though I’m getting better at removing the fuel rails now)

I”m not sure it’s that whole bank - that wouldn’t explain why number 2 was 20 degrees cooler than 1 and 3 - to me that would be more of an indication that 2 isn’t firing but 1 and 3 are and the cooler No 2 is bringing the temps down for 1 and 3. Not sure why number 2 plug is so sooty though if it isn’t firing - that doesn’t add up.

With the air flow sensor I’ve replaced the barn door with a MAF sensor so there’s no plate to move


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[Nine One One]

Its all a bit weird

The black sooty plug should mean it is running too rich, so you would expect it to run cooler as it ignites at a lower temperature. I think you are correct that it is not firing, and the 88°either side is heat transfer to the middle cylinder. The middle cylinder having no heat in it will also help cool the other two either side and lower their temperatures.

Take it the HT leads are actually fine, they produce something but are they breaking up inside?

What if you take an injector from the other bank, swop it with number 2 and see if that transfers the problem to whatever side you took the different injector from and cures number two?

I think you adjusted the valves when the engine was out, the intake valve is not too tight on number two so it is not getting enough air in.

[sladey]

Thanks - they are both interesting thoughts and things that I can check on

I think the HT leads are OK. They are perhaps 10 years old and seem to be good quality and in good condition. They are also producing spark to the spark tester

I agree that if we’ve got fuel before the injector and spark in the combustion chamber, that would seem to point at something wrong with the injector.

However it is odd that the symptoms are more or less the same both before and after all the injectors were changed.

Also it doesn’t account for the sooty plug - if it’s not letting the fuel through there wouldn’t be ignition so I’d expect a clean plug wet with fuel. If it’s not letting enough fuel through then that would be too lean and wouldn’t produce the sooty plug (I don’t think)

I could well have got the tappet adjustment wrong (I seem to have fcuked up most of the things I’ve touched this time!) - so potentially it isn’t letting enough air in to burn OR it is burning but it isn’t letting the mixture out - that might explain the sooty plugs and be the reason it’s not working properly - when the next air and fuel comes in it’s already full of burnt exhaust gases.

Think I’ll check the tappets again tomorrow.

Edit:- found this from uncle Google:-

Tighter valves will not make any new noise. When the intake valves get too tight they will cause hard starting and poor idling. When the exhaust valves get too tight they will also cause hard starting and eventually get hot enough to start melting - not pretty.

[sladey]

Now the deadline for the Pyrenees holiday has passed I’m enjoying this analysis process much more

[rhd racer]

It’s a fair point - going back to first principles, what has changed? You have discounted the fuel pump, injectors and stale fuel from the car standing for a while. You then potentially damaged the loom and have repaired that, and found issues with the ECU and repaired that also. Therefore, looking at the tappets again seems pretty sensible.

Good luck tomorrow


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[RobFrost]

I'd compare that spark plug with others from the same engine, taken at the same time. I agree this is probably limited to the left bank, and probably just to once cylinder, but it'd be good to be sure before you invest too much work in that hypothesis.

I think the tappet hypothesis is a good one. My first thought was a leaky injector, but it sounds like you've swapped those and the problem remained.


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[impmad2000]

Hi Mark, I have had problems in the past with what sounds very similar horrible missfire that I couldn’t nail down. Typically this happened after not being run over winter. In each occasion a new set of spark plugs fixed it. More recently I have switched to a hotter plug, runs hotter and so self clears so much better. Straight away the engine got its “pep” back.
My hypothesis is that the fuels are different and degrade quicker. Our older engines need a hotter plug to compensate. Degradation over winter is high, the plugs are contaminated in the 1st run. Hotter plug seems to have fixed it.
Might not be the same for yours, but might fix it. Worth a try. Your car, like mine has modern ignition on an old engine, so could be another similarity.

[sladey]

Thanks Tim. However they actually are new spark plugs. That soot is after two trips of about 5 miles.

Out of interest what hotter plugs did you switch to?

[sladey]

Ok so when I did the tappets when the engine was out I was in a quandary about finding TDC.

I’ve got the Z1 mark on my pulley so that’s fine it’s just that I can’t easily tell if it’s on the compression or exhaust stroke

I don’t have a distributor any more so using the position of the rotor arm is a non starter.

As I’ve read back over my earlier notes I can see I seemed to have problems establishing it was on the compression and had a go until it seemed to be going wrong and then started again.

I know if it’s the compression one then both tappets should be loose and adjustable - however that is assuming I did it right last time and I don’t want to start from assumptions.

So this time I want to be certain. I’ve ordered a compression testing kit which should arrive this afternoon.

In the meantime I thought I’d try and make something simple myself. I took an old spark plug and using the lathe tried to drill down the middle (the aim being to attach a tube and a balloon to the other end - the compression stroke would inflate the balloon).

After I’d ruined two drill bits I realised the spark plug option was a non-starter.

Then I got a piece of tubing with an OD of 16mm and with a Stanley knife tried to shave it down to 14mm so I could stuff it in the hole.

I cut the finger off a rubber glove and attached it to the other end and jammed it into the hole.

I then did 2 rotations of the crank but no movement from the finger.

When I checked it hadn’t jammed into the hole at all.

I’m just going to wait until the compression stuff comes now as that will make it much easier to know for certain that I’m on the compression stroke.

[Gary71]

Good plan.

You'll also be able to tell if you've got no compression i.e one valve tightened up so much it doesn't close properly.

[impmad2000]

Thanks Tim. However they actually are new spark plugs. That soot is after two trips of about 5 miles.

Out of interest what hotter plugs did you switch to?

That’s my point. They soot up and can’t self clear. Hotter will burn off the soot. I think the ones in at the minute are WR5DC+ but start with what you have and choose one stage hotter. The Bosch seemed better than the NGK. After all a simple think to try.