whtltng89

I asked this same question last winter with no results. Ive got a 91 5.7 L TBI thats giving me fits.When it gets down to about freezing outside it runs like crap. It lopes to the point of stalling at idel and misses.Will barely pull its self, to get going.Fuel filter, temp sensor,knock sensor chkd for vac leaks and chkd all conections, everything is getting correct voltage. Timing is right on the money. At road speed it will only run good at WOT.Any one got any ideas how air temp can effect running?If I put it in my heated shop and let it warm up it will run just fine. OK, This morn I started it and it ran like **** ( 17deg) and no surprise. Let it run for 20 min and shut off.Came back 1 hr later and it still ran bad,drove to work a and at noon ran perfect for about 2 miles then hesitated and started missing.Had lunch ran bad again,8 hr later started and ran perfect. I also noticed a pinging sound like it was out of time and soft backfiring thru the muffler.Oh before I forget the cat was removed long ago. Sometimes I can shut it off and restart and it will solve the problem,but it might be temp. or it might last a day or two.

Formula 305

Who tuned it after the 5.7 swap? Maybe they didn't add enough fuel for cold weather conditions? It'd be real real difficult for anybody to point you in the right direction without a lot more information. Who knows what could have been messed up when it was swapped.

whtltng89

I never said it was a swap this is a factory motor w/320k miles on it

Bob88GTA

iTrader: (2)

TBI or did you mean TPI? What's it in?

Formula 305

No car came from the factory with a 350 TBI, so either its a swap or its a 5.0, or your talking about a vehicle other than a 3rd gen and giving us no information on the vehicle. So how about you help us help you and fill in some of the blanks.

RBob

iTrader: (1)

Sounds like it's your work truck... If you have a spare ignition coil to try, swap it on.

RBob.

whtltng89

Ok,my bad,I forgot to put in its a 91 siverado 4x4,Thats having the same problem as it has whenever it gets cold,(and ONLY when its cold.)) I started here because its a TBI and Im not to familar with them. The coil has been chkd numerous times and replaced.I asked this same question last year and didnt get a response,so here I am again. Ive been working as a mechanic for 50 yr or so and this thing has me stumped. It also has a friend of mine stumped .lol

RBob

iTrader: (1)

Have you checked the sensor values via a scan tool? When acting up, have you wiggled sensor and actuator connectors? Reminds me of a line printer issue I troubleshoot years ago. It would tend to print garbage, and when it did, it would do it for some time.

On a hunch I removed the cable between it and the mini-computer and laid it out in the sun. Printer worked perfect with the hot cable, once it cooled off (data centers are cold) the printer produced garbage.

The terminal to wire crimps in the connectors were bad.

RBob.

whtltng89

All the sensors were replaced if they didnt give me a good spec.and all the connections and wiring have been chkd several times.Ive got it in my heated shop right now and am going to if itruns good or not. As Ive said before, air temp is what causes it to run bad and at times it runs good. The problem of it being so random is whats making it so hard to find. Im going to chk the coil again but air temp would not affect it as far as I know.lol

Schurkey

X2 on the scan tool, but not just for sensor inputs. I'd want to know what the O2 sensor is doing while it's acting-up, and also the short- and long-term fuel trim numbers. How cold is the engine according to the coolant temp sensor? Does that number seem reasonable? Is the knock sensor active, and retarding timing? What is your fuel pressure when the engine is running poorly?

One time I fixed a "runs-shitty-when-cold" TBI, the distributor cap, coil wire, and rotor were completely fried. The carbon button on the cap was gone, the spring blade of the rotor was eroded, and the coil wire was open on my ohmmeter. How it ran when warm is a total mystery to me.

ImBrandon

Maybe the cold weather creates a vacuum leak due to shrinkage. Have you been spray gum cutter/ starting fluid to check for vacuum leaks.