Need Help - Strange Acceleration Question
Thread Starter
Instructor
Joined: Aug 2002
Posts: 246
Likes: 18
From: Menlo Park CA
Need Help - Strange Acceleration Question
I have a 92 LT-1 stroked to 383. It's been having a strange problem when accelerating recently. If I take the rpm's fast, as soon as I get to 4000 rpm, the engine cuts out and starts to stumble badly. If I take the rpms up to 4000 slowly and then continue to accelerate slowly up past that, it has no problem. If I take the rpms up above 4000 slowly and then floor it, the cutting out happens at that point. The problem is more pronouced in 1st and 2nd gear since it seems that the engine revs more quickly past 4000 rpm in the lower gears. The engine isn't getting something it needs fast enough.
I have a brand new MSD opti-spark in the car and the car was doing this problem on occasion before I put the new opti-spark in(I had other issues with the old broken opti-spark).
I'm wondering if this could be fuel pump/fuel system or possibly vacum related
Any ideas out there on where to start looking? I hate these problems that can either be fuel or electical!!
Thanks for any ideas that can be provided.
Last edited by Vestor; Oct 3, 2007 at 02:09 AM.
Burning Brakes
Joined: Dec 2006
Posts: 936
Likes: 2
From: Tyrone PA
Sounds like you are running out of fuel. If you haven't changed the fuel pump yet I would buy a walbro (edelbrock) 255lph (67gph) pump and see if that clears up the problem. If you already have a high volume pump then I would check fuel pressure, which you will need a gauge and long hose to do while you are driving.
Racer
Joined: Jun 2006
Posts: 408
Likes: 0
From: Elkton MD
High RPM miss
Either lack of fuel, failing spark or restricted exhaust.
Check the fuel pressure and try to interpret whether the pump is failing. Is the filter reasonably new?
Check the spark by raising the hood at night in a dark area (disconnect the under hood lamps) and have someone rev the engine. Any visible sparks is not good.
My bet is that the exhaust is restricted by a fractured cat. I had a Buick that performed similarly to your symptoms and it was a fractured cat honeycomb. The rapid exhaust evidently caused the broken pieces to accumulate and plug up the exit of the cat housing. Another symptom was that under the missing condition, the air came out the 'wrong' vents (floor and defrost rather than the dash vents). This resulted from the engine vacuum being screwed up by the exhaust back pressure.
I put on new cats and examination of the old one revealed the broken honeycomb pieces. And the car wound out really tight with the new cats.
Yes, we used to put a potato up the school bus tail pipe so it couldn't reach good speed. A really fat potato kept the bus from even starting.
Good luck.
Check the fuel pressure and try to interpret whether the pump is failing. Is the filter reasonably new?
Check the spark by raising the hood at night in a dark area (disconnect the under hood lamps) and have someone rev the engine. Any visible sparks is not good.
My bet is that the exhaust is restricted by a fractured cat. I had a Buick that performed similarly to your symptoms and it was a fractured cat honeycomb. The rapid exhaust evidently caused the broken pieces to accumulate and plug up the exit of the cat housing. Another symptom was that under the missing condition, the air came out the 'wrong' vents (floor and defrost rather than the dash vents). This resulted from the engine vacuum being screwed up by the exhaust back pressure.
I put on new cats and examination of the old one revealed the broken honeycomb pieces. And the car wound out really tight with the new cats.
Yes, we used to put a potato up the school bus tail pipe so it couldn't reach good speed. A really fat potato kept the bus from even starting.
Good luck.
