v8 misfire

shawser · Post by **shawser** » Tue Apr 19, 2011 6:35 pm

Hi folks, just joined tonight, so hello to all of you.My question is this, iv got a mk2 hilux with a rover 3.5 v8 fitted, the loom was shot so fitted anew one, i also replaced valley gasket, new dizzy cap, plugs and leads, the timing was never touched and it was running fine before i did the loom and valley gasket. now it wont start, but it misfires and spits back through the holley carb, the plugs spark fine and its getting fuel, i did tke the carb off to clean it, could i have possibly done something to carb? hope someone can help as its starting to get to me and stopping me finishing my project. cheers to all.

ChrisJC · Post by **ChrisJC** » Wed Apr 20, 2011 6:52 am

Did you remove the distributor?

Chris.

shawser · Post by **shawser** » Wed Apr 20, 2011 8:24 am

no the dizzy was never removed, iv checked timing at no1 plug on tdc and all seems fine, im thinking its a fuel problem,as the intake manifold and holley carb was all that was removed.

Stu E · Post by **Stu E** » Wed Apr 20, 2011 12:39 pm

May seem obvious, but are the new leads on in the right order?

jefferybond · Post by **jefferybond** » Wed Apr 20, 2011 3:56 pm

If it's misfiring and spitting back, then fuel is definitely getting in there and being lit by the plugs, so it's most likely going to be ignition timing.

If you haven't touched the dissy then the leads are probably in the wrong order.
Jeff

DEVONMAN · Post by **DEVONMAN** » Wed Apr 20, 2011 5:57 pm

I tend to agree with the idea that the leads are not correct.
(18436572 with the dizzy turning clockwise).
However, another thing to check is the rotor arm.
Is it a points or electronic dizzy? They both have different height rotor arms and the wrong type may shoot random sparks to different posts in the cap.

Regards Denis

shawser · Post by **shawser** » Wed Apr 20, 2011 7:43 pm

leads are on correct, been checked so many times and a friend of mine also double checked. Dizzy is electronic. it was running fine with old cap, and the same rotor arm thats still in, nothing has changed in the ignition side, if i try with new leads, cap and plugs it misfires, if i put the old stuff back in its the the same, so im still leaning to the carb as i said its the only thing that was removed along with intake manifold.

Ian Anderson · Post by **Ian Anderson** » Wed Apr 20, 2011 8:26 pm

Have you got all the vacuum ports on the carb blocked?

If not your mixture will be all to buggery

Ian

Ian Anderson · Post by **Ian Anderson** » Wed Apr 20, 2011 8:27 pm

Have you had a big backfire?

If so the Holley will need a rebuild

Ian

shawser · Post by **shawser** » Wed Apr 20, 2011 8:47 pm

i did notice that there were no vac pipes coming from dizzy, so will need to check carb, also yes had a big backfire, but im going to order parts for holley anyway. So do you think its more to do with carb, intake rather than ignition timing?

Ian Anderson · Post by **Ian Anderson** » Thu Apr 21, 2011 7:47 am

Just asking the easy diagnostic questions

Big backfire normally means Holley Power valve needs replaced

Ian

DEVONMAN · Post by **DEVONMAN** » Thu Apr 21, 2011 8:28 am

Ian Anderson wrote:Just asking the easy diagnostic questions

Big backfire normally means Holley Power valve needs replaced

Ian

If the power valve is blown then the float chamber will empty into the manifold, so it should be obvious if that is the case.
(ie massive flooding and possible hydraulic lock.)
Regards Denis

jefferybond · Post by **jefferybond** » Thu Apr 21, 2011 8:33 am

You said you checked the timing while number 1 cylinder was at TDC, but:

a) Was no. 1 on the compression stroke? (ie, timing 180 degrees out)
b) Are you sure you had the correct no.1 cylinder (front right looking at front of engine?)

I've made both of these mistakes in the past!

Jeff

shawser · Post by **shawser** » Thu Apr 21, 2011 10:42 am

I know what youre saying, but as previously stated, the dizzy was never taken out or moved and car was running fine before i took off inlet manifold and carb, so the timing cant just all of a sudden jump 180 degrees out. thats why im convinced its a carb issue.

DEVONMAN · Post by **DEVONMAN** » Thu Apr 21, 2011 11:33 am

shawser wrote:I know what youre saying, but as previously stated, the dizzy was never taken out or moved and car was running fine before i took off inlet manifold and carb, so the timing cant just all of a sudden jump 180 degrees out. thats why im convinced its a carb issue.

When you say you cleaned the carb I assume you mean the outside.
If you inverted it, then a load of crud in the float chambers may have become dislodged and is now blocking the idle/transfer gallery.
Some engines do cough back through the carb when the mixture is very lean or there is an inlet manifold leak, but this is different to a misfire.

If you are convinced that the ignition leads are ok then it seems that removing the carb and checking it is your best option at this stage.
Regards
Denis

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