1987 3.2 Carrera Backdate project - Sladeys hotrod

[markm]

That just bad luck mark, these things happen and probably giving it to a fresh pairs of eyes when you get back isn’t a bad thing

I’m fairly sure you will still have a good time on your holidays in the GT4

[sladey]

Thanks guys.

In the middle of the night I started thinking that the problem could still be with the injection loom. I know it got stretched when I first removed the engine and I know some of the wiring has splits in it.

I checked for shorts but didn’t check each plug for continuity. If there was a semi-break then it would affect the pulsing of one or more of the injectors and give the symptoms I’ve been experiencing.

When I get back I can try some tests on each individual injector - or just put a new one in

[DustyM]

I’m still thinking air leak or
Mixture problem, the fact that it runs better as you increase the revs is what has me thinking this. The more revs the less impact a small air leak has on the mixture.

Also are you running a MAF or do you
Still have the barn door?

An injector problem wouldn’t go away
as the revs rise, it would get worse surely?

But all guess work. I’d take a look for you Mark but don’t have the facilities I used to.


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[sladey]

I think I’m maybe not explaining it very well. It was rough in different ways throughout the rev range. At about 4k it sounded more normal but when I lifted off it sounded wrong as well.

I don’t have enough experience listening to bad running engines

I’ll also admit I tend to jump at one diagnosis.

I have gone through looking for leaks quite thoroughly though and really couldn’t find any - spraying carb cleaner at the base on the inlet stacks also produced no change at all

[Bruce M]

Once you get back, some diagnosis using the ECU software & laptop should get to the root cause.

Can the software record a log file?

[sladey]

Yes it does - I’ll try that when I get back

[Jonny Hart]

Thanks guys.

In the middle of the night I started thinking that the problem could still be with the injection loom. I know it got stretched when I first removed the engine and I know some of the wiring has splits in it.

Given that the injector driver circuit in the ECU was damaged, that could certainly have been caused by wiring in the loom being shorted to ground.

[sladey]

Also looking at the things I fcuked up during the work suspending the engine by the injector loom probably wasn’t good for it

[markm]

Awesome work mark. That could be the problem

[RobFrost]

I think checking manifold temps was good advice. The more you can narrow down the possibilities, the less guesswork is required.

Then I'd probably clip a timing light on each spark plug wire.

Soon you'll know which cylinders are affected and whether it's fuel or spark.

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[sladey]

OK so the saga continues…

The new injector loom arrived. However it wasn’t marked as to which set of injectors was on which side

I referred to the wiring diagram


And peeled back the boot on one of the connectors. Sussed out the colour scheme which meant it was number 4. I then did the same for No. 4 on the existing loom and the colours matched.

At this stage, rather than spending ages fiddling around with the P clip on the far side of the engine that holds the loom in place, I just unplugged the old loom and plugged the new one in - I can fit it properly later.

I started it up and it seemed to be a lot better - certainly smoother than it was before - but it was still trying to idle too low. I couldn’t really tell at idle though so I took it for a test drive.

It is not sorted.

So it is substantially better than before but still feels like it is not running on all cylinders - the engine is not smooth at any revs - it always sounds a bit lumpy. When pressing on the power isn’t there - I mean some power is there but nothing like what I’m used to.

I drove it for a while and got it up to temperature. It didn’t change, and whenever I stopped it wouldn’t idle - it either seemed to be trying to idle at about 300 rpm and it stalled - or just just died when I stopped.

So I got it back into the garage and dug out the temperature sensor that I’d previously bought for the house radiators.

This told a story:-



So the right hand side (4,5,6) were all consistently about 105 degrees.

On the left hand side, 1 and 3 were around 88 degrees but No. 2 was 64 degrees.

Now allowing for heat soak (or lack of it) I’m surmising that No 2 isn’t firing for some reason and the fact that there is no heat coming from no 2 has meant that 1 and 3 are lower than the other side.

So the problem appears to be No 2

[sladey]

I’d worried that the ECU problems hadn’t been fully fixed but thinking about it, the ECU sends a signal to one bank or the other - if it was ECU related then I’d be getting nothing on one bank.

So it’s fuel or spark on No 2

It’s got a new loom, new injectors and new spark plugs.

I say new, but the spark plugs have been sat in a box for about 15 years as I’d previously bought them and never fitted them.

I could take that one out and swap it for one of the previous ones (cleaned up) - I’ll probably do that first

For it to be fuel, the brand new injector could be failing (which I think is unlikely) or there could be a blockage in the fuel rail.

I’ll start with the spark plug

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[sladey]

Ok so I took no 2 plug out


Bearing in mind this was brand new and I’ve driven it round the block a couple of times it seems unusually sooty.

So I grabbed one of the previous plugs, cleaned it up and put it in.

Started it up and no change. Rough running and won’t idle

[sladey]

OK so then I connected an inline spark tester to make sure spark was getting through

https://youtu.be/f6xSVKkzPuM?si=59JXx3rPc2hOa9Aw

So it is producing spark to the plug

I suppose fuel is next


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[Bootsy]

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