y5mgisi
1 ton status
I have no advise to offer other than good luck!
CK5
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Cooling System Overhaul - Stumped and Frustrated
- Thread starter dhcomp
- Start date
I'd crank up fuel pressure, you didn't tune this thing did you after the header/engine swap? Running lean is a given if the cam and exhaust want more fuel.
If you are suspecting a vacuum leak, I'd put a vacuum gauge on the motor before I started it, and watch what happens. If it's a vacuum leak, you will see it, especially since the idle improves.
But my suspicion is that you have a fueling problem. It happens when cold because the pre-programmed fuel mix is wrong for the difference in engine/exhaust. It's a suspicion, could still be something else, but I'd not be leaning towards swapping another hard part when it may be that the already-done swaps are what cause the issues.
If you are suspecting a vacuum leak, I'd put a vacuum gauge on the motor before I started it, and watch what happens. If it's a vacuum leak, you will see it, especially since the idle improves.
But my suspicion is that you have a fueling problem. It happens when cold because the pre-programmed fuel mix is wrong for the difference in engine/exhaust. It's a suspicion, could still be something else, but I'd not be leaning towards swapping another hard part when it may be that the already-done swaps are what cause the issues.
I haven't tuned it, but the only thing that isn't stock is the external TBI mods, and the headers. The crate motor was an exact GM replacement.
Now that you say fueling problem, i DID swap the previous injectors into this setup. I ordered performance ones from CFM tech, but when they didn't work, i installed the stock ones. Wonder if these are doing something weird under throttle....although, they have a nice clean spray when i watch them.
hm.....
have you done a plug reading?
it's a tool that is so often ignored it's sad... so much can be derived from the subtle differences in a plug..... it's one of the first things I'll do is throw a new set in, than check them after a few hr's run time... than again after x hr's, rinse/repeat...
I would be inclined to think fuel too, as I'm guessing/remembering what the overheat issue was... running hot under tow load at speed correct? with that kinda airflow, it shouldn't be a rad/fan issue..
pressure test has nothing to do with what pressure the system is working at, etc, it's strictly to let you know what leaks you have.. most importantly cracked head, gasket and such.. not so much a drippy hose... tho that stuff should be fixed just for accurate testing.. I'm also guessing your running a 14 or so psi cap and not like a 7psi?
it's a tool that is so often ignored it's sad... so much can be derived from the subtle differences in a plug..... it's one of the first things I'll do is throw a new set in, than check them after a few hr's run time... than again after x hr's, rinse/repeat...
I would be inclined to think fuel too, as I'm guessing/remembering what the overheat issue was... running hot under tow load at speed correct? with that kinda airflow, it shouldn't be a rad/fan issue..
pressure test has nothing to do with what pressure the system is working at, etc, it's strictly to let you know what leaks you have.. most importantly cracked head, gasket and such.. not so much a drippy hose... tho that stuff should be fixed just for accurate testing.. I'm also guessing your running a 14 or so psi cap and not like a 7psi?
And if doing a plug reading, needs to be done during the time it gets hot, no? TBI is going to fix a fueling issue (rich or lean) when it's in closed loop up to a point, plugs will look good unless you are way out of tune, and normally start running into the CEL if it's that bad, which this doesn't sound like.
If motor was exact replacement, to include cam, then not likely as much of an issue, but headers are worth ~25HP on a small block, and that's a significant amount of increased airflow. I'd still throw a vacuum gauge on there if you have lingering doubt about a leak.
If motor was exact replacement, to include cam, then not likely as much of an issue, but headers are worth ~25HP on a small block, and that's a significant amount of increased airflow. I'd still throw a vacuum gauge on there if you have lingering doubt about a leak.
yup, TBI plugs always look great.... one wire O2's save the world.. 
Ethanol in our fuel today also makes plug readings less accurate. They can look better than what you actually have.
Haven't checked plugs since the motor went in, but mostly cause they are so tricky to fish out with the headers.
Running a 3 wire o2 after the header install. I'll pump up the fuel pressure for now, check for intake leaks with propane, then see what happens. Thanks!
Running a 3 wire o2 after the header install. I'll pump up the fuel pressure for now, check for intake leaks with propane, then see what happens. Thanks!
y5mgisi
1 ton status
Just out of curiosity, did this start around the time of the headers? I ask because Pinsco63 on here had a 3 wire o2 on his burb that we tried forever to figure out the problem on. It would idle up and down hard until it died. Finally I un plugged the o2 sensor and it idled silky smooth again. New o2 sensor fixed a problem that a previous new 02 caused.
Problem has sorta been around for a while. I got a check engine light with the original o2 when i put the headers on, heated o2 sensor cleared that problem. No other issues associated, as far as i know.
This truck has always run like crap when cold, but i always figured a new motor would fix that. Wrong.
I have a similar problem but I'm chalking mine up to a 230,000mi + motor. Anyway, I was looking at the Redline stuff you mentioned and the reviews on Summit are all 5 star and most claim a 10°coolant temp drop. For what that might be worth.
Installed the intake.
Definitely had a leak on the exhaust crossover, and a number of the bolt threads were leaking.
Sealed around the coolant and exhaust passages on the felpro gaskets, reassembled, and sealed all the bolt threads with thread sealant.
I hope i get better at this every time!
Edelbrock manifold fit fine, only issue was one of the tensioner braces bolts to a hole that wasn't drilled/threaded. Figure i'll run with one brace. Wasn't about to drill/tap a new manifold.
Other than that, fit like stock, and even at a bit higher, fit fine under the hood with TBI spacer.
Truck runs a bit stronger, but still idles pretty weird cold.
Just drove it to work today, and operating temps / behavior seem about the same.
Current fuel pressure is at 13psi, going to crank up to 15 and see what happens.
Besides adding some coolant additive, i'm out of ideas.
I'm sure towing with a bike rack on the new front receiver will really help cooling issues too.....
Frustrated.
Definitely had a leak on the exhaust crossover, and a number of the bolt threads were leaking.
Sealed around the coolant and exhaust passages on the felpro gaskets, reassembled, and sealed all the bolt threads with thread sealant.
I hope i get better at this every time!
Edelbrock manifold fit fine, only issue was one of the tensioner braces bolts to a hole that wasn't drilled/threaded. Figure i'll run with one brace. Wasn't about to drill/tap a new manifold.
Other than that, fit like stock, and even at a bit higher, fit fine under the hood with TBI spacer.
Truck runs a bit stronger, but still idles pretty weird cold.
Just drove it to work today, and operating temps / behavior seem about the same.
Current fuel pressure is at 13psi, going to crank up to 15 and see what happens.
Besides adding some coolant additive, i'm out of ideas.
I'm sure towing with a bike rack on the new front receiver will really help cooling issues too.....
Frustrated.
y5mgisi
1 ton status
After that, my only idea would go back to the o2 sensor. I dont remember what we talked about there. But its possible that it could be reporting a constant rich condition to the computer. The computer then leans out the mix as hard as it can.
That would make it run hot, but is pretty far fetched.
That would make it run hot, but is pretty far fetched.
Don't remember that suggestion.
Totally possible. Especially after going to the heated 3 wire and headers.
Any way to check it? Or just throw a $20 one at it?
y5mgisi
1 ton status
Personally, i would disconnect the battery for a while to clear the memory out of the computer, then just un plug the 02 and take it on a short drive that you know would normally get it to overheat. It will never enter closed loop and will run at the factory default perimeters the whole time. It will run fine. obviously only for diagnostics.
Not a horrible idea.
I've also got a few years and some miles on this o2 sensor. Didn't change with the motor.
Thanks for the idea.
I've also got a few years and some miles on this o2 sensor. Didn't change with the motor.
Thanks for the idea.
y5mgisi
1 ton status
Ill tell you a quick story. A buddy(pinsco63) has the same truck you do. 91 3/4 ton burb, tbi350 4l80e. It didnt run good. So he put a three wire o2 in. Still didnt run good but ran about the same. THen started getting so bad that it would actually die at idle. We tried forever to figure out what the hell was going on with that truck! Everything you can think of! Then, i thought, hell with it, why dont i at least see how it runs with the o2 simply unplugged. Truck ran like an effing dream! New oe style 1 wire o2 sensor later it was up and running better than ever.
THe point is, it might not be your o2, but its easy enough to just unplug it to see if makes a difference.
THe point is, it might not be your o2, but its easy enough to just unplug it to see if makes a difference.
Interesting. I only went 3 wire cause i couldn't' get the check engine light off with the headers. Wonder if i kept the old one.
Definitely worth a shot to unplug. You know how i hate diagnostics, but this one is easy enough
y5mgisi
1 ton status
I would be very curious to see how it runs with it unplugged. If it runs like crap, something is wrong. Cause the factory perimeters are fairly close. In other words, o2 sensors can often mask a problem, and they can also give pseudo problems.
Again, im not betting this is your problem, but again again, its so easy to find out. And free!!! Which is a good thing after all you have been through with this thing!
Again, im not betting this is your problem, but again again, its so easy to find out. And free!!! Which is a good thing after all you have been through with this thing!
Yep. I'll give it a shot.
Went to adjust the rear brakes, and one adjuster is corroded solid
Its only been a couple years since the axle swap and brake rebuild!
