VT 5.0 stumble when throttle openend quickly

[shane1]

Hi Guys,
We have a curly one here, its a 1997 VT 5.0 running CJDP, it is totaly stock (we think).
Basically it came to us after every man and their dog has played with it. It runs fine but had a very poor idle, and when the throttle is opened quickly it hesitates and sometimes stalls. if opened slowly its fine.if opened from 1200rpm its fine , only if snapped from a low idle.
run on the dyno it makes about the right power(140rwkw).
we diagnosed an inlet manifold gasket leak pulled the manifold fixed the gasket . Now it idles perfect.
But the hesitation is still there..... my first thought was the distributor (new replaced by previous shop)
was installed incorrectly and upon inspection was , so reset the dizzy with the cas correctly aligned, as i thought the cam sensor being out could affect the sequential injection, and as the fault is only as you grab the throttle off idle i thought it may fix it .Have tried another air flow meter (known goodone ) but still no better. there is no fault codes other than a strange intermittant cas/cam one ,which we put down to the previous shop having the wiring jammed hard against the manifold. so now im thinking the new dizzy could be an issue. Anyone else ever had this........

[vlad01]

likely ignition related, a break down of spark when suddenly loaded up.

mine was doing the exact same thing, only when opening the throttle too quick and it stumbled for a sec then fine. was a faulty coil. V6 but the principals are the same.

[shane1]

New coil , dizzy and wiring harness thanks to the last guys ....

[vs ss]

Just throwing ideas out there but I had one doing similar things on hard take of and it ended being a hole opening up in the rubber pipe between t/b an maf when the engine tilted.

[HQ355]

Chinese coil ? Chinese dizzy ? The fact it's throwing occasional codes is telling you something isn't happy in there, just cause parts are new dosnt mean there ok

[Holden202T]

got a fuel pressure reading ? or exhaust AFR's when this happens ?

[immortality]

Does it still have a standard throttle body or has it been fitted with a bored out unit?

[shane1]

fuel pressure ok, alternative injectors tried, tps replaced , standard throttle body . Intake pipes ok,hasnt thrown a code since we put the dizzy in the correct spot.Im going to pull a rocker cover and ball part lift at tdc on overlap, somethings not right ....

[j_ds_au]

I once had misbehaviour in a car long ago, also when the throttle was opened quickly from idle. I can't remember the symptom now, but the cause was an engine mount, in which the rubber block had de-bonded from the metal.

Joe.

[shane1]

It was the non genuine distributor. Replaced with the original unit good as gold.