'97 4.3L Vortec will not start when cold

[Robert_H]

Hello,

I own a ’97 Chevy S10 extra cab with the 4.3L Vortec engine that’s close too the 149,000 mile marker; for the past 2+ years, the truck will not start (or have a lot of difficulty doing so) when the temperature outside falls below (approximately) 70 degrees. I’ve found “priming” the intake system by removing the air intake duct from the throttle body, adding a splash of gasoline (about 2 tablespoon) in the throttle body (butterfly in the closed position), and putting the intake duct back on; the engine will fire and run without difficulty. After running 1 to 2 minutes, I can turn the engine off and start it again as I normally would. Once the truck has started and warmed up, it will run pretty much as normal, “except” for an occasional hi-rev “sticking”…when the throttle is (completely) backed off, the RPM’s will hesitate falling to idle speed (about 800-900 RPM’s). I can drive to work at 8:00 am (about 25 to 45 minutes one way) and usually be able to start the truck without priming it “IF” I leave work before the temperature falls below 70. If I start/run the truck at noon, then try to start it at 7:00 pm that same day, the truck will not start without being manually primed first. If anyone has any input or ideas, I would greatly appreciate them!

Here are some of the facts:

1) Fuel pressure is 56 psi when starting cold.
2) Fuel pump replaced about 9 months ago…had same issue prior to pump replacement.
3) Fuel filter replaced one month ago
4) No error codes are displayed
5) IAT sensor replaced
6) Fuel pressure regulator replaced
7) Fuel meter body cleaned
8) Idle Air-Control valve replaced
9) Intake plenum cleaned and gaskets replaced
10) I know that the RPM issue is not a mechanical issue with the throttle body
11) I live in the Phoenix, Az. Area and have “NO” issues in the summer


Thanks,
Robert

[hsmda]

This has to be a fault in either the system that reads coolant temp. or the system that enriches the mixture when the coolant is cold. Look at the coolant temp. sensor first. It that's OK, check the wiring from it to the computer. If that's OK, it's probably the computer.

[handymandp]

I had the same problem and had to replace the spider assembly..

[camohog1]

my '91 will do something similiar. On the times when it will not start does it lag like it is trying to start or just not turn over at all? If it will not turn over at all then I dont have a clue, sorry. What kind of air intake do you have? Because it sounds like it may be getting gas, but no air. Just my 2 cents worth. You might also try changing the fuel pump. Even though it was changed 9 mnths ago, sometimes you will get one that will act up and need to be replaced sooner than another one will.-Aaron

[Robert_H]

Thank you all for the ideas...

I thought that it would be the coolant temperature sensor, so I pulled it off (making the circuit open) which makes it the coldest reading, but it had no effect.

When you make reference to the spider assembly, are you referring to the module which houses the fuel injectors?

Yes, the engine alway turns over; at least until the battery runs dead from trying to start so many times. As soon as you add a dab of fuel, it fires right up and runs; that is...until you shut it off and don't try starting it again until the engine has cooled down to 70 degrees or less...then it's the same all over again.

Robert

[GDBSKE]

Pulling the plug off will make it go to the coldest setting true. But the computer will detect an open circuit and defalt to a "warm engine" setting. In other words, this test is useless. Doesn't mean anything.

[dmbrisket 51]

engin defalts to -32 and primes it as so, it will not correct, and can set a code for cat efficency on a post 02 cat, it will load up on a cold start with the sencer unplugged

[GDBSKE]

I just unplugged one of these today, it defaults to "warm engine". Notice that Robert H pulled the plug and it "had no effect". If it mixed the fuel for -32 degrees the engine would barely run or maybe not at all once it got warm. It would load up very badly when warm.

Something is definitely wrong with your cold start. Sensor, wiring, PCM, or injector, although if it was the injector I would think you would have some full throttle driveability problems also.

[dmbrisket 51]

if anything the whole system goes into limp mode wich isn't a warm engin condition, and yes, the moter does run rich as hell with the sencer unplugged... 97 was the start of the sequential fireing and he probibly has a crack in his spider lines going to the injector, could be a million other things, but having to guess online i would guess that.

[williams george]

robert h my 97 s10 4.3 did the same as yours i put every thing on engine checked fuel pressure 56psi it should be 58psi to 60psi i replaced the fuel pump. $3oo.00 my truck starts good now. williams george