ZL - rough idle, pinging, ignition problems

[Unlucky8Ball 6]

Hi everyone,

 

My EFI ZL has a weird thing going on with the ignition timing, it's had a rough idle since I bought it which I thought was a vacuum leak.

 

Tested for it and replaced all the vacuum accessory lines but no luck.

 

Then I took it onto a freeway with a full car and noticed it was pinging pretty hard, and soon enough the temperature gauge hit the top end and had to pull over.

 

Checked at home with a timing light, and the timing mark is so far advanced it's off the scale. But when I adjusted it to be 10 degrees at idle with SPOUT connector off, it barely even idles when in D with the brakes held down.

 

Haven't owned an EFI car before, and have no clue what controls the ignition timing or what could cause it to do this. Bad distributor? ECU?

 

Cheers

[Clevo120Y 815]

Does the ZL have the ignition controlled by the ecu or is it still the XE style electronic ignition?

[Jiminy Kriket 133]

My experience with the EFI 250 is that the slightest little vac leak means the engine won't want to idle properly. My old man's zl needed the vac lines replacing, the rear engine seal, intake gaskets and the rocker cover gasket doing, and it still has a minor fluctuation while in gear. The idle control valve at the back of the rocker cover can sometimes get a build up of crud in it and need cleaning, and while you're in there replace the o ring for some insurance.

On the pinging issue, what year model zl? is it the leaded EFI or unleaded EFI version. The unleaded version has a knock sensor and is a little more tolerant of lower octane fuels. The leaded EFI motor, which my dad has, didn't get the knock sensor. Makes it real touchy to timing and fuel octane rating. He's gotta run 95 minimum just to keep the thing from rattling it's head off. 

I think i've covered everything we've done so far. If not, i'm sure someone else will chime in.

[SPArKy_Dave 8,881]

You might need to get a hold of a an Air/fuel ratio gauge, and see what the mixture is like.

http://www.innovatemotorsports.com/products/MTXL.php

 

There is some 'mixture' adjustment, at the air flow meter near the air box.

 

Two things first though -

 

1. verify that TDC on the balancer, is the engine's true TDC. - so you know your timing marks are accurate.

2. try disconnecting and plugging off, the brake vacuum booster hose, and see if that makes any difference.

[Crazy2287 1,886]

What sparky said. Verify your TDC!

 

+1 rotate the crank over by hand and make sure you dont have a TDC and a BDC mark. If you do, do something so you can tell them apart under the timing light. I was chasing a timing issue for hours on a mates car before i found the dizzy was a tooth out and i was actually setting the timing off the BDC mark

 

ANY AIR that gets past the AFM will lean the AFR and cause hot combustion temps which can contribute to detonation. So you gotta make sure all your vac lines are 110%

 

Pull your spark plugs and inspect them for detonation and colour.

[VDO 124]

Pinging is also often a sign of a blown head gasket, due to coolant leaking into the combustion chambers... hence the rise in engine temp.

[Unlucky8Ball 6]

I'll get around the checking where TDC sits soon, but I was inspecting the distributor just then and noticed that there's a hissing sound (like a vacuum leak) coming from it - it stops at certain points in the distributor's adjustment.

 

It's a TFI distributor, so no vacuum advance.

 

Could this have something to do with it?

[Valvebouncer 2,389]

Pinging is also often a sign of a blown head gasket, due to coolant leaking into the combustion chambers... hence the rise in engine temp.

 

This. Check the basics first, oil water then timing AND especially the balancer for slip. Go buy a TeeKay tester to test the head gasket. As other eluded to, a vacuum leak, don't forget to check the seal under the oil filler cap too.

[Lord_fahrquhar 2,580]

slipped balanacer?

[bear351c 10,271]

XF/ZL also had issues with the inlet manifold warping along the length of the head. Again, causing vacuum leak.

Overheating and rough idle, indicates timing is out, so as others have suggested check TDC is TDC.

Rocker cover must seal well, too.

 

Let us know if ya find out what it is.

[Unlucky8Ball 6]

What's the best way to test for TDC without specialised equipment?

 

I've read about putting a long screwdriver down the spark plug hole in cylinder #1 and seeing when it hits the top, is that reliable enough for this purpose?

[Clevo120Y 815]

A physical stopper is the best way, a hollowed out spark plug with a bolt through the centre will work, I remove the rockers so valves don't touch the stopper, turn the motor over until it stops (by hand) and mark the balancer in line with the tdc mark on the timing cover, turn the motor until it stops in the other direction and mark the balancer again, measure between these 2 marks is true tdc and hopefully that will be marked on the balancer already if it hasn't moved.

[bear351c 10,271]

Yep, like Stumper said. ^ ^ ^.  You can use a screwdriver, but, BE CAREFUL !!!  Alloy pistons, alloy head, Sparkplug threads, etc.....

2 man job would be best. Disconnect the battery FIRST, so no-one can crank the engine, accidentally.

Wind the crank with a socket on the balancer bolt, hold the screwdriver free of the sprkplug threads and fully inserted in the plug hole. Slowly turn the engine over by hand, when the screwdriver stops rising, and both valves are closed, on No 1 cylinder, you are approximately at TDC. The physical stop is better and more accurate, but, if you're just checking to see if the balancer has slipped, this will do the trick.