engine problem?

[martinlaw]

Hi,

Can anyone help?

I am not very mechanically minded but I know some of you out there are experts.

My engine is a 5.7 with fuel injection and a 'optical' distributer with Edlebrock Performa heads and cam (approx. 450bhp) Sometimes she runs fine, but other times (particularily under 2000 rpm)the car starts 'kangarooing' and the only way to stop this is to dip the clutch. Nothing is touched from one day to the next. The engine is never particularily smooth when off or on part throttle, but when you put your foot down it pulls like a train right through the rev range.

Any ideas???

Thanks,
Martin.

[US-GTR]

A few things that could cause this situation (easiest listed first)

1) "Lugging" the engine. Trying to be in a gear that is too high for the given RPM.

2) Ignition too advanced. Poor/no low RPM response, runs like mad at upper RPMs.

3) Possible vacuum leak. Same operation as #2, but with an added bennefit of higher temps.

[martinlaw]

Hi Joseph,

When the engine is running ok it will pull off from 1000rpm no trouble at all.

Ignition timing is a thought but why would it change from one day to the next when it is controlled by the ECU?

Will check for any leaks.

Thanks for the input.

[thevet]

Sounds very similar to a fault I had on my LT1 poered cobra, which was due to corrosion of the optispark distributor which you may have on your engine perhaps, moisture got in and worked havoc with 30kv flying through. It was visually obvious that the distributor was the problem due to corrosion, so have a look and see. Bes of luck Tim

[bobrush]

hi martin
the car has always done that it is because you are in to higher gear for the speed you are driving i asked the same questions when i got the car hope this helps

bob

[gtrclive]

Are you sure it's not just the Race engine Over Caming effect.... You will find when you have a cam with overlap then low end rpm will produce what you have, if you try to maintain a constant speed in a high gear with low rpm. The higher the cam overlap the greater the effect will be and at higher rpm...

My 420ish bhp chevy with a 244 degree duration (@.05" lift), caused this below 1500rpm. If say I tried to keep 1400 rpm in 4th gear on a level road then it felt like Kangaroing. Now say the same speed, gear and rpm up a hill then it would not do it because the engine is under load. The same engine could pull away from a standing start in 4th, and pull from 500rpm to 7500 with no problem. This is a atribute of what happens when you have a Overlapping cam.. So want the horse power from a normaly asperated chevy then unfortunatly this is what happens....

Andy GTT's car that had nearly 500bhp did this upto about 1800rpm..
But lets face it most american cars with these engines are auto's so this problem would not happen with them.....

[Boosted LS1]

Sounds like snatch/surge to me ie when there's to much ignition advance at some rpm's which shows up when in the wrong gear.

Boosted.

[jschwartz]

It's normal for a light car with a performance camshaft in it.