1986 GMC K3500 4X4 454 GAS stalls and won't start for 30 mins

ngodline12 · September 13, 2020

my 1986 454 has an interesting and annoying issue. it starts and runs fine. I tow a trailer over to my buddies house 15 minutes away. I leave the engine running while we unload, takes about 10 mins. then when I leave his house, the engine quits and won't start for 20-30 mins. once it starts it runs fine again. it does it exactly the same way every time. it did exactly the same thing when I went to another destination. it quit as soon as I left the premises and wouldn't start for 20 mins. I have changed the carb to a QF 750 thinking the original was done at 115K miles. it has an electric fuel pump that the last owner installed. I put a fuel pressure gauge in it to see if its a fuel delivery issue. I have changed the entire ignition system so new pugs, wires, cap, rotor, coil and ignition module. It idles and runs fine and at higher rpms the engine is rock solid with no missing or anything. I tried to recreate the conditions at my house to get it to fail where I can deal with it but I couldn't get it to do it. my next course of action is the EGR system. I checked the EGR valve and it moves fine with no sticking. when I move it with the engine running it has an effect so I think that part is working. I will need to get a vacuum gauge to check further. anybody got any ideas? I'm ready to push it in the river...

Edited September 15, 2020 by ngodline12

riverbanks · September 13, 2020

Sounds like a bad power feed wire or fusable link,check those links,the ones leaving the starter, running up the back of motor,do a wire wiggle test,see if it stalls,or with a test light, check for 12v at large red wire at distributor when it's a no start

ngodline12 · September 14, 2020

I just tried an experiment. I left the hood up when I was at my buddies house and shut the engine off. it made it home no problem. so something is overheating in the engine compartment. im thinking near the top as that's where to engine heat would pool. I will set up a spark plug simulator so next time it does it I can see if there's spark.

ngodline12 · September 15, 2020

I tried wiggling all the fusible links I could find and it still runs fine. is there a ballast resistor or some other electronic thing that is hidden somewhere? of course now it seems to be behaving itself so I can't check for 12V at the distributor.

riverbanks · September 15, 2020

Nothing hidden that I remember,did you install Icm properly?with the goo?

ngodline12 · September 15, 2020

yes. the dielectric. the original looked dry.

on the fusible link. the number stamped on the plastic. is that the gauge?

I found the wiring diagram and I don't see anything on there that it could be. my next course of action is to be ready when it quits and see if its getting spark.

Edited September 15, 2020 by ngodline12

CamGTP · September 15, 2020

Could be vapor lock in the fuel line/carb.

ngodline12 · September 15, 2020

I thought that too. however there is fuel in the site glass on the carb bowls and all the lines are rubber leading up to the carb. and the line is pressurized to 6.5 psi