Hello,

I have a very specific issue with my 1984 Pontiac Trans AM. It is a stock, automatic, 93K mile 305 LG4 car with the E4ME. I am not a carburetor expert but know some basics and want to learn more. .

Just for baseline, The car runs and drives perfectly except for this one issue which I am attributing to fuel boiling/hot issue (The car does have that blower motor that hooks to the fuel line and runs after the car is turned off for a bit I believe this was GM’s way of trying to solve fuel boiling/vapor lock). . The choke is fully opened when the car is hot as well and I have run a few cans of Berryman B12 through it.

So here is the specific issue. When the car is driven and gets hot, when the car is turned off and it sits for 3-4 hours upon restart the car will run very erratic at idle (i.e. almost like it is going to stall, the RPM’s wonder between 400-500 rpm in neutral and lower in drive…) If I put in Drive, I have to feather the pedal to keep it going BUT once I start driving, it is fine. If you come to a stop minutes after the has been restarted hot, the car has now returned to normal and not threatening to stall.

I have been writing this off to hot fuel in the lines, bowl, etc. but just curious is anyone else has thoughts to maybe resolve. I have been reading this may be because of a “week” ICM, Coil but again this car runs 100% at all other times.

Again this is the only issue so just curious is it a “live with it” or anything else I can try / look for to see if I can resolve it.

 

Sounds like heat in the fuel pump. The block of course gets hot, and transfers the heat to the pump. When the fuel sits in the pump for awhile and gets hot, then emerges from the line where the pressure keeps it from boiling into the fuel bowl at atmospheric pressure, it explodes into foam like shaking up a Diet Coke bottle and then taking the top off.

Replace the block-off plate with one of these. https://www.summitracing.com/parts/ctr-85-000

 

This is a tough one. I like the idea of the phenolic spacer, but I don't think it will make much difference since the mounting bolts are still transferring heat from the block to the pump, and also the pump arm itself. Maybe a combo of the phenolic plate and insulating washers under the bolt heads?

 

I've had this problem before, and just adding an extra blockoff plate gasket and fuel pump gasket cured it. That's what put me onto the Canton part. The phenolic spacer makes a YYYYYYUUUUUUUUUUUUUUUUJJJJJJJJJJE difference to the fuel pump temperature.

Butt yeah, no doubt adding fiber or nylon washers under the bolt heads, and maybe drilling out the pump a bit and adding nylon or some such spacers around the bolts, would further add to the isolation. I've never gone quite that far though.

 

Thanks for the replies. All good suggestions. I will perform the recommendations and update. Thanks again!

 

I think I will modify the (2) 3/8" bolts for nylon washers like this:

I will drill the pump holes to 7/16" (they are probably really close to that already) and turn down under the head of the bolt to 5/16".
I might have to put a slit in the nylon washer to get it on the bolt. I hope they will not melt.
https://www.digikey.com/en/products/...WS3001/9676391