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Hesitant take offs

thatK30guy

thatK30guy

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The truck is a '91 K5 with a 5.7, 4L60, 241, 10's with 3.73's, yada, yada, yada.

When I bought it from another member on this site, it idle very roughly. There was almost no "get up and go" when it was put in gear.

Then I let it sit for about a year.

Today I was planning to tune it up with all new plugs, wires, cap, rotor, fuel filter after a friend put it on a scanner and pulled no code.
He did say the oxygen sensor was not working like it should. But once the truck got warmed up, it ran better.

Today I started out by tracing the plug wires very first thing before even attempting to remove them. I found out #6 and #8 were crossed over. I immediately pulled them and put them back in their right plugs, got in and started the truck and VOILA! It runs! Real smooth idle, plenty of power, no hesitation. Until you put it in gear and start moving.

A little sluggish. Almost like its choking. Give it a lot of gas and it gets moving no problem. I took it on the highways to "break it in" from sitting so long. Got home and checked the fluids of which I had to put a quart of motor and tranny fluids in. Upon restarting the truck, its slow to start, like chugging. Its not the battery because its fully charged.

What other things should I look at? I'm gonna replace the oxygen sensor no matter what. Anything I should do or look at to get it to start right up as soon as the key is turned? Anything to check to keep it from hesitating?
 
Possible low fuel pressure at the throttle body? IIRC it should be 9-13 psi, ideally at 12 or 13. Lower pressure would mean a less good pattern from the injectors which could affect starting. Have you checked the pattern on the injectors? Could be they're a bit gunked up from sitting/old fuel...

Have you checked base timing? The initial stumble could be the timing a little retarded...

Rene
 
Will relay these ideas to my friend with the scanner and go over it with him. Keep the suggestions coming if anyone has more.
 
Mine is having the same stumble right off of idle in gear. 91 350, tbi.

Was tuned up about 15k ago, with plugs, wires, cap, rotor, fuel filter, PCV.

Any ideas? I'm going to squirt something flamable around the tbi gasket, besides that, and checking plug wires, im stumped. Any ideas?

Timing is set at 1 or 1.5˚. On the factory tab, is that 1 or 1.5˚ retarded? Or advanced? The timing mark dealy only goes one way from zero on mine.....
 
Check your coil. Mine was pretty bad and the 4l80e shifted funny till I replaced the coil, been 20k since then and all is well. I went with the MSD coil for the same money and a little more work.

Also I'm pretty sure that the timing should be set to 0 degrees, the computer does the rest..
 
jonathon said:
Check your coil. Mine was pretty bad and the 4l80e shifted funny till I replaced the coil, been 20k since then and all is well. I went with the MSD coil for the same money and a little more work.

Also I'm pretty sure that the timing should be set to 0 degrees, the computer does the rest..
Click to expand...

How do you test a coil?
 
I didn't have to test mine since it was obviously bad so I'm not real sure. On mine the connection was really corroded and when the truck was idling you could hear and see tiny sparks coming out from under the boot and grounding on the intake :eek1:
 
Put a new O2 sensor in and the new filter. No change.

After the truck gets warmed up/hot, it runs good and goes from a dead stop. After I drive it around for a while and it gets hot, then it dies when I come up to a stop sign or slow down to almost a stop.

I went out to a friends house tonight and was looking at his house for work to do. I shut off the K5 and went in house with him for about 30-45 minutes. When we got done, I went to leave and almost couldn't start the K5. Once started, it just didn't want to idle worth crap. After a few minutes of faster idling, it finally got warm enough and made it back to town. Still sluggish when leaving the place. Once on the highway it levelled out and ran smooth.

What do I check for now? Another friend thought the fuel pump might be weak.
 
Injector(s) could be bad as well, but just guessing, still many possibilities.

Getting good fuel spray when it's running, keeps up when throttle is increased?
 
Yeah, it keeps up but only when the engine is hot blooded.

If I shut it off and let it sit even for 15 minutes, it runs rough again until it gets hot. Then it goes fine. Until I come to a stop or slow down to a stop, then it dies/almost dies.
 
Checked the cat? Sounds a little like a plugged up cat...

Rene
 
What do I do there? Remove it and ram something inside it to clean it all out and make it a straight-thru type?
 
thatK30guy said:
Yeah, it keeps up but only when the engine is hot blooded.

If I shut it off and let it sit even for 15 minutes, it runs rough again until it gets hot. Then it goes fine. Until I come to a stop or slow down to a stop, then it dies/almost dies.
Click to expand...

What I meant was what happens when you have the air cleaner off and watch the fuel spray as its running, increasing the throttle?

Not much load, so not much additional fuel demand, but it could show a problem with leakage, pressure, injector pulse, etc.
 
Clean the battery terminals, pull the idle air motor and clean. Check fuel pressure. Check grounds on the thermostat housing and inspect distributor drive gear (iffen you got lotsa miles on yours).
 
thatK30guy said:
What do I do there? Remove it and ram something inside it to clean it all out and make it a straight-thru type?
Click to expand...

Somewhat cheap way is to remove it and replace with a piece of straight pipe. You should be able to manage to do that without ruining the cat, so if it isn't a problem and you need to run one where you live you can weld or bolt it back in.

Rene
 
Check and clean the Egr valve. Also ck the vacumn lines. The Egr is active below 1500 rpm after the engine is at temp. Try replacing the IAC as well. Good luck. Brian
 
what size tires are you running??? soounds like a lot of different things but if your running 35" tires or bigger you might need to go to a proper gear.
 
dyeager535 said:
What I meant was what happens when you have the air cleaner off and watch the fuel spray as its running, increasing the throttle?

Not much load, so not much additional fuel demand, but it could show a problem with leakage, pressure, injector pulse, etc.
Click to expand...
Will check today. ;)
 
pilate74 said:
Clean the battery terminals, pull the idle air motor and clean. Check fuel pressure. Check grounds on the thermostat housing and inspect distributor drive gear (iffen you got lotsa miles on yours).
Click to expand...
Battery is new and just installed. Everything is clean on that.

IAC will be checked today also.

Motor has over 200K on it. What all exactly is involved in checking the dizzy on these engines? I'm not exactly a rocket scientist with the FI motors. Guess I'm too old school.
 
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