Holy shit that is ALOT of info. Reminded me of college listening to my chemistry professor. I didn't understand most of it.
Gonna digest this today.
Gonna digest this today.
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.
**FIXED!!**DEFINITELY***Super HIGH idle after multiple parts replacement - TBI 1990 K1500 350engine
- Thread starter ZombieK5
- Start date
Engine was not hunting during that vacuum reading but it was very steady. I'll do it today while it's hunting.
I'm fairly certain there isn't a leak around the TBI. Low fuel is possible but even at 10psi steady fuel pressure I am in the acceptable range. Exhaust leak is unlikely. I have new manifolds, new gaskets along with an entire new exhaust system all the way to exhaust tips. I'll check manifold bolts torque today. Probably need to do it anyways since it's gone thru a few full cycles.
I did find a YouTube video of a guy with a similar problem. He replaced intake gaskets and fixed the issue. While I have no problem doing this myself, the vacuum leak (if that's the real problem) should be present 100% of the time. There are times when the engine doesn't surge and seems to run fine. That makes me think the issue is electrical.
Last edited:
Swaped out TPS. Put NEW sensor in and voltage is up to .74 with key on.
NEW EVIDENCE BELOW!
MAP code has not come back.
Swaped out old O2 sensor and I haven't had Lean Code come back.
Still runs like crap. I took it for a spin around the block and it didn't like it. It didn't stall but it ran like crap.
Parked it and it doesn't want to start.
Timing seems fine when MAP sensor is unplugged. I took some readings with MAP unplugged.
I plugged in the original NEW MAP sensor I bought and condition didn't change.
NEW EVIDENCE
MAP Plugged in.
I pulled the vacuum hose off the EGR solenoid and the engine ran fine with idle at 775-825
I plug the hose with my finger and it starts to surge.
I put hose back on EGR solenoid and I get ZERO vacuum on the other two nipples (one goes to EGR and the other is the "breather" nipple).
View attachment 20250510_134909.mp4
View attachment 20250510_135054.mp4
NEW EVIDENCE BELOW!
MAP code has not come back.
Swaped out old O2 sensor and I haven't had Lean Code come back.
Still runs like crap. I took it for a spin around the block and it didn't like it. It didn't stall but it ran like crap.
Parked it and it doesn't want to start.
Timing seems fine when MAP sensor is unplugged. I took some readings with MAP unplugged.
I plugged in the original NEW MAP sensor I bought and condition didn't change.
NEW EVIDENCE
MAP Plugged in.
I pulled the vacuum hose off the EGR solenoid and the engine ran fine with idle at 775-825
I plug the hose with my finger and it starts to surge.
I put hose back on EGR solenoid and I get ZERO vacuum on the other two nipples (one goes to EGR and the other is the "breather" nipple).
View attachment 20250510_134909.mp4
View attachment 20250510_135054.mp4
gmbellew
Registered Member
egr hose being open and running good means it is needing more air to be happy. that just creates a vacuum leak. try adjusting the min air idle screw to open the blades a little. IAC should come down a bit and the air will be going across the throttle blades to better atomize the fuel vs going through the IAC.
has someone previously messed with the min air idle screw?
i can't remember, was it running well before you did all this work.
has someone previously messed with the min air idle screw?
i can't remember, was it running well before you did all this work.
It ran fine before this. EGR nipple at the TBI was 100% blocked with carbon.
The EGR solonoid hold vacuum. I am guessing that is bad. Shouldn't it breath from the nipple that usually has the foam filter on it??
Last edited:
gmbellew
Registered Member
the EGR solenoid should hold vacuum on the valve port, yes.
if the EGR port was plugged, the ECM may have learned around that. disconnect the neg terminal to clear the memory so it will relearn. that could help. although EGR solenoid is closed at idle (or is supposed to be) so I wouldn't think that idle would be affected.
were any other ports plugged?
if the EGR port was plugged, the ECM may have learned around that. disconnect the neg terminal to clear the memory so it will relearn. that could help. although EGR solenoid is closed at idle (or is supposed to be) so I wouldn't think that idle would be affected.
were any other ports plugged?
Last edited:
Getting Closer...
OK, the engine was warm when I disconnected the EGR vacuum hose connected to the TBI. Engine ran great when I let the vacuum suck air freely. If i blocked the vacuum hose (like what happened when it was connected to the EGR solenoid) The engine would bog down and run bad.
Disconnect MAP sensor - engine runs great
Allow EGR vac hose to freely suck air - engine runs great
I allowed engine to cool. Just started it and it surged like always HOWEVER the EGR vac hose was sucking air....Engine ran bad. IF I blocked the EGR vac hose NO CHANGE.
So, I have a Massive vacuum leak (EGR vac hose) and engine runs but surges. I block vacuum leak (EGR vac hose) and NOTHING changes.
I am now thinking this is 100% electrical. The coil is new but the dizzy is still OEM and original. When warming up the dizzy should advance and then back off after engine starts to reach operating temp. I replaced the rotor on the dizzy. The old one was in horrible condition. I did not replace the pickup coil but i also did not inspect it.
Photos below show the old fuel regulator vs new regulator and new spring.
Old Distributor rotor and inside of old distributor cap
Old Coil - I replaced it
OK, the engine was warm when I disconnected the EGR vacuum hose connected to the TBI. Engine ran great when I let the vacuum suck air freely. If i blocked the vacuum hose (like what happened when it was connected to the EGR solenoid) The engine would bog down and run bad.
Disconnect MAP sensor - engine runs great
Allow EGR vac hose to freely suck air - engine runs great
I allowed engine to cool. Just started it and it surged like always HOWEVER the EGR vac hose was sucking air....Engine ran bad. IF I blocked the EGR vac hose NO CHANGE.
So, I have a Massive vacuum leak (EGR vac hose) and engine runs but surges. I block vacuum leak (EGR vac hose) and NOTHING changes.
I am now thinking this is 100% electrical. The coil is new but the dizzy is still OEM and original. When warming up the dizzy should advance and then back off after engine starts to reach operating temp. I replaced the rotor on the dizzy. The old one was in horrible condition. I did not replace the pickup coil but i also did not inspect it.
Photos below show the old fuel regulator vs new regulator and new spring.
Old Distributor rotor and inside of old distributor cap
Old Coil - I replaced it
gmbellew
Registered Member
i'd definitely throw on a new cap and rotor....those look well worn.
might also think about plugs/wires, not sure their condition or age, given how the cap/rotor have been neglected.
might also think about plugs/wires, not sure their condition or age, given how the cap/rotor have been neglected.
Already replaced cap and rotor and new wires and new plugs
After all the new parts, with all the vacuum lines connected, after clearing codes, how long has the been allowed to run? Has it been driven at all, under above conditions?
Those tbi dist are a weak link. I have replaced 100s of them, back when GM still made them. Finding a good replacement these days is the rub.
Need scan results with everyting connected in closed loop.
Minium air procdure should be done after any changes to fuel system.
Those tbi dist are a weak link. I have replaced 100s of them, back when GM still made them. Finding a good replacement these days is the rub.
Need scan results with everyting connected in closed loop.
Minium air procdure should be done after any changes to fuel system.
Drove around the block a few times. Ran mediocre at beat but didn't die. I've also let it idle for over a hour several times. Burned avout 8 gallons with all the idling.
Summit has an HEI direct replacement available for $110 plus $44 for an HEI Coil
I have scan results in closed loop. They should be above in the 2nd video after truck was warm.
I reset IAC after any changes and clear codes too. What is your minimum air procedure?
With the distributor in bad shape and then I add a new coil, rotor, cap, wires and plugs maybe it is too much for the other electronics inside the distributor and it isn't advancing correctly?
gmbellew
Registered Member
the ignition control module advances the timing. it can be replaced easily. make sure you use a AC Delco and also use the thermal paste on the bottom. but I am not sure that is the issue. but it is always good to carry a spare in the glove box anyway....
I really don't see how the issue is not electrical. I created a massive vacuum and I plug it and unplug it and the surging doesn't change. I have removed and replaced the TBI gaskets and nothing has changed. The TPS and map sensors both appear to be functioning normal. I replaced the new oxygen sensor with the old oxygen sensor and the readings on the scanner were the same.
I have not tried to start the truck cold with the map sensor unplugged. I've always had the engine warm when that happens so timing Advance is not an issue. When it is surging it almost feels like it's trying to advance the timing and then fails and Falls backward to a retarded position.
gmbellew
Registered Member
not sure. the fueling is all over the place when it is surging also, but the O2 voltage is continually in the lean range.
if the IAC counts are at 60 for warm idle. that is too high. you need to turn the min air idle screw a little to open the throttle blades. this will let the IAC close and more air will be passing over the blades and the fuel atomizes better. get the IAC counts to 30 or less and then see how it does. as long as the TPS is still less than 0.9v or so, you don't need to bend the tab. although some folks do like the voltage to be closer to 0.5-0.6v at idle. but the ECM reads the voltage at each start to reset the baseline.
if the IAC counts are at 60 for warm idle. that is too high. you need to turn the min air idle screw a little to open the throttle blades. this will let the IAC close and more air will be passing over the blades and the fuel atomizes better. get the IAC counts to 30 or less and then see how it does. as long as the TPS is still less than 0.9v or so, you don't need to bend the tab. although some folks do like the voltage to be closer to 0.5-0.6v at idle. but the ECM reads the voltage at each start to reset the baseline.
Understood.
I am just leary adjusting that screw.
I've had too many sources coming to me saying the screw should NOT be touched and that is specifically why GM put the cover over it. Their logic is that the idle was set at the factory for the specific TBI unit and the other parameters need to adapt to the adjuster screw position.
My question would then be if the screw needs adjusting why did the surge not alter when I created the massive vacuum by unplugging the vacuum hose from the EGR solenoid? The thing that is perplexing me the most is the engine running fine with the EGR solenoid vacuum hose disconnected which creates a massive vacuum leak.
The vacuum leak created with the EGR vacuum hose should have changed everything. The only thing that I can conclusively deduce is that the distributor was trying to compensate by advancing the timing but failing because there is an Distributor issue. From my reading, a failing map sensor, or a disconnected map sensor, causes the distributor to be forced into a full-time advanced position that does not change. That would suggest the surging issue is from the distributor trying to advance and adjust timing but failing.
There's too many parameters with this and it should be a whole lot easier than this is. This is much simpler than the fuel injection system on my Toyota Corolla but the Toyota Corolla fuel injection system is so much easier to diagnose and repair.
gmbellew
Registered Member
I agree that the adjusting the screw is not a routine need. however, your IAC counts are somehow out of spec. that can affect idle, or GM wouldnt have a spec. whether they were out of spec before is unknown. how they got out of spec is also unknown. was the IAC passage clean on the TBI when you cleaned it?
id not argue about trying a new AC Delco ICM. because if swapping it doesn't resolve the issue, put the old one in the glove box as a spare. the rest of the distributor, besides the pickup coil, is all mechanical.
you might look at the data stream over a longer idle period. does the O2 voltage ever got above 0.5v? there should also be a rich/lean parameter. does it change or is it always the same?
id not argue about trying a new AC Delco ICM. because if swapping it doesn't resolve the issue, put the old one in the glove box as a spare. the rest of the distributor, besides the pickup coil, is all mechanical.
you might look at the data stream over a longer idle period. does the O2 voltage ever got above 0.5v? there should also be a rich/lean parameter. does it change or is it always the same?
IAC passage is very clean. Double checked it.
Guessing the cheaper method is just putting in a new ICM. I found a cheap one to throw in to see if it changes anything. If that does the trick then I'll just swap out a whole brand new distributor. I'm sure it's worn out anyways with 250,000 Miles on it.
The data screen pretty much shows lean the entire time. I need to see if I can change the settings on the data stream. The 02 readings are all over the place. It's been down in the 90's then there have been other times when it has been in the 800s but even other times when it even other times when it has been steady in the mid to high 400s.
I'm guessing that I need to divide those numbers by 100 to get the actual voltage.
436.7 = 0.4367
gmbellew
Registered Member
I think the O2 voltage is displayed in mv.
if a new ICM fixes it, I'd just keep rocking the old distributor.
if a new ICM fixes it, I'd just keep rocking the old distributor.
Agreed. However, I've seen the internals of these old Distributors and the internal pickup coil are usually corroded badly which creates really bad resistance. It's a 35 year old truck with the original distributor. It just may be good insurance to replace it while it's in the garage then on the side of a highway.
