Popping through intake
Thread Starter
Heel & Toe
Joined: Mar 2023
Posts: 24
Likes: 4
Popping through intake
I have an 86 vette with a 90 motor, I just replaced the head gaskets, plugs, wires, distributor, injectors, timing set at 8 degrees advance. It’s hard to start when it’s sat for a little while maybe loosing fuel prime, when cold it’s running rough but once warmed up idles smooth but when you give it gas it tries to die and pops through the intake. I’ve rechecked the timing, plug wires and exhaust to see if it’s plugged checked for vacuum leaks with smoke machine and tried spraying starting fluid all around the intake while running and everything seems fine. This car was barely running when I got it which is why all the work has been done to it, but I’m currently lost on what’s wrong with it now, could it be a fuel system problem causing this issue?
Zen Vet Master Level VII
Joined: Mar 2016
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From: Southlake, TX
Can you give more info?
Thread Starter
Heel & Toe
Joined: Mar 2023
Posts: 24
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Can you expand on this a bit more? If you are spraying fluid and the car runs better, then you have a fuel starvation issue. If you spray around the intake manifold area and the car smooths out you have a vacuum leak do to poor gasket seal.
Can you give more info?
Can you give more info?
Pro
Joined: Aug 2020
Posts: 647
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From: Liliha Bakery stuffing my face with coco puffs!
I'm gonna pose the question of...is the '90 engine from a Corvette and didja swap the entire engine 1 for 1??? The '86 intake would have came with a cold start injector and the '90 would not. Unless you swapped the '86 TPI on to the '90 engine then that would be moot. The '86 engine comes with a 100k ohm knock sensor whereas the '90 engine comes with a 3.9k ohm sensor. I would not think that this would cause a start up issue but it would trigger a SES light which in turn would attribute to reduce timing off idle. Could be a '86 cast iron head vs '90 aluminum head that calls for a different spark timing map. Come to think of any of these timing issues may attribute to a pop in the intake. Confirming fuel pressure is a good idea as well.
Last edited by stew86MCSS396; Apr 8, 2023 at 02:17 AM.
Thread Starter
Heel & Toe
Joined: Mar 2023
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Pro
Joined: Feb 2009
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From: Vancouver Washington
Fuel pressure should be above 40 psi at idle and above 42 when revved.
Something in that region. I don't have my FSM in front of me at the moment.
When was the last time the fuel filter was changed?
Something in that region. I don't have my FSM in front of me at the moment.
When was the last time the fuel filter was changed?
Thread Starter
Heel & Toe
Joined: Mar 2023
Posts: 24
Likes: 4
I just changed the fuel filter today, fuel pressure went up to 25psi now with it, I just got a new fuel pump going to put that on this evening or in the morning
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Pro
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From: Liliha Bakery stuffing my face with coco puffs!
Wow I just read your other thread, it's interesting that it seems someone went through great lengths to put the '90 top end on the '86 engine along with the ECM so disregard the cold start injector. Knock sensor comment still applies if you're getting a code 43. I wonder if pinching off the return line would improve fuel pressure hinting that it might not be the fuel pump but if you acquired a new pump might as well change it...