P38A V8 Not starting after head gasket change

Just replaced both the gaskets. Still running very rough, cuts out if I let it idle. The heads were torqued correctly, 20nm - 90 - 90.
The injectors for cyls 4 6 and 3 5 have enough length of cable for them to be connected the wrong way, although they are currently connected where the cables do not have any stress/pull on them.

there should be no stress on the cables.

what about plenum gasket.. new or refused? and inlet manifold gasket.. new or re-used ?

In normal circumstances, if she's drawing air, the engine will initially rev up, then stumble & die or run very erratically, revving up & down.

I think there may be more than one factor here. All of the above or at least some of the above, sucking air and weak sparks.

Are the plugs in good order?

Are the leads in good order?

Are the coils in good order?

Are the plugs making good contact with the leads and/or coil tips?

And possibly, do you perhaps have a leak at the head gasket? I have seen someone drop something onto the gasket and drop the head on, then bolt it down and ruin the machined surface. It wasn't pretty.

I also did the head on a 2.0 Vectra. Guy bought it, head gasket had been done, lasted 3 months & went again. Got it done again, 3 months and it went again, so he brought it to me. I cleaned up the block, rubbed my finger tips over it and felt the tiniest bump, like a smooth grain of sand near cylinder 4. Rubbed it with sand paper till it was perfect, stuck it back together and 9 months later it was still running when the gearbox went He gave me the car, I took out the engine & put it in another Vectra, which I ran for 6 months, sold it and 4 years later it was STILL running perfectly. Guy who bought it said it was the best Vectra he'd ever had

The lesson here being, do it right, do it once.... I'm not suggesting you made an arse of it, but things can and do go wrong & you may not even be aware of it

But do the checks and take your time about it. If everything checks out and you suspect the gasket or mating faces, do a compression test.

Plenum gasket and inlet manifold gasket both new.
I just got it to idle without cutting out, although it was rough.
But when I revved and let it drop back down, it stalled again.
It seems letting the revs drop will cause it to cut out.
Plugs are in good order, leads in good order, coils are in good order, all plugs making good contact with the leads, except for one which I can't push on properly with my own strength.

Going for MOT tomorrow so may ask the mechanic to run some basic tests

d1s said:

Plenum gasket and inlet manifold gasket both new.
I just got it to idle without cutting out, although it was rough.
But when I revved and let it drop back down, it stalled again.
It seems letting the revs drop will cause it to cut out.
Plugs are in good order, leads in good order, coils are in good order, all plugs making good contact with the leads, except for one which I can't push on properly with my own strength.

Going for MOT tomorrow so may ask the mechanic to run some basic tests

Click to expand...

Where about are you based? Perhaps someone on here is nearby & could pop over...

d1s said:

Plenum gasket and inlet manifold gasket both new.
I just got it to idle without cutting out, although it was rough.
But when I revved and let it drop back down, it stalled again.
It seems letting the revs drop will cause it to cut out.
Plugs are in good order, leads in good order, coils are in good order, all plugs making good contact with the leads, except for one which I can't push on properly with my own strength.

Click to expand...

my guess from that is that its sucking in un-metered air giving a too weak mixture.

What other places could air be seeping in from? All connections, from the air box to the intake, are sealed tight

after the intake.

when i did my 3.9 it ran lumpy and petered out at idle.. i took the plenum chamber apart and down to the inlet manifold, i missed a bit of seal on the plenum chamber, sealed it all, torqued up the inlet manifold again to get a good gasket seal after it went back together no problem.

So I should be using gasket sealant along with the gaskets?

Just RTV in the notches between block & heads before putting the valley end seals on (i do run a little under the end seals for good measure). Make sure the metal clamps are properly in place & not catching on the lower intake. Some do put a little RTV around the coolant galleries between the head & valley gasket. If yours is a thor then no sealant between the upper manifold / lower manifold, just the metal gasket (if it's britpart then you might need to open up the holes for the locating dowels on the gasket - mine didn't fit last time). Not sure about the gems?

Just had a look in my spare bits box - found the new valley gasket seals inside
Looks like I forgot to fit them. I'm sure that isn't helping

i dont think there's sealant on the upper to lower plenum chamber either just the gasket. i'll know more when i get around to replace the valley gasket on mine, have everything ready to go.. except the the desire to do it

While you're doing the valley gasket check the wires to the injectors. These cars are getting old and those injector wires get fragile, especially when pulling them about doing gaskets.

d1s

Martyn is your guru here, he's done more head pulls then probably anyone on here.

ukadamwest said:

d1s

Martyn is your guru here, he's done more head pulls then probably anyone on here.

Click to expand...

Maybe there is a reason for that.

Just fitting the new heads with ARP's.First one on & felt much better with studs, on with second now. Maybe I am doing something wrong but follow rave to the letter & pretty meticulous about everything. Still putting it down to weak threads in block.

martynv8 said:

Just fitting the new heads with ARP's.First one on & felt much better with studs, on with second now. Maybe I am doing something wrong but follow rave to the letter & pretty meticulous about everything. Still putting it down to weak threads in block.

Click to expand...

probably.. on that 'other' site it seems going to ARP studs is the preferred and common choice.

of course they are 'murricans so get confused with things like hood, fender..... and which side the steering wheel is supposed to be on.

wammers said:

Maybe there is a reason for that.

Click to expand...

Wammers your such a git!! ;O)

ukadamwest said:

probably.. on that 'other' site it seems going to ARP studs is the preferred and common choice.

of course they are 'murricans so get confused with things like hood, fender..... and which side the steering wheel is supposed to be on.

Click to expand...

In days of yore nuts and studs were commonly used on alloy heads, until they found out that the different expansion factors made them loosen up in use. That is why they started using stretch bolts that expand and contract so that bloody great dished cavities are not formed by constant expansion and contraction of the alloy head under the head nut washers.

Mark Piercy said:

Wammers your such a git!! ;O)

Click to expand...

I say as i see.