A bad MAP can give all kinds of drivability problems. They aren't that much so i would say change it. especially if you have never changed it before.
CK5
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1995 Yukon - Strange Stall
- Thread starter BigBen
- Start date
Just went out and looked it over. The vacuum line is good and the connector is fine. I guess this means I'm ordering a new sensor. Hopefully this will get rid of the problem.
(and it's still the original, so I guess I might as well change it)
-Ben
Just a thought here, is the lockup converter unlocking?
could it kill the engine if not?
Shifting it to park and restarting it might be resetting it. Each time it dies you are coasting or stopped, right?
could it kill the engine if not?
Shifting it to park and restarting it might be resetting it. Each time it dies you are coasting or stopped, right?
If the TCC did not unlock when he stopped he wouldn't be sitting at a red light idling.
Just a thought I had. I have a 2003 GMC company truck that surges sometimes when stopped at a signal light that I thought might be the TCC acting up.
Back to the drawing board.
Back to the drawing board.
Thank goodness you thought of that, I've been trying to figure out if it was related!
On another note, I spent most of last night reading up on ALDL and trying to figure out what I need to do. (The "injection section" rocks!)
From what I can tell, I've got the 8192 Baud connection. (I don't even have a pin in the 160 baud spot). I think this means that I can't use Win-ALDL and that I need to make the different 'two-transistor' cable shown on some of the pages.
I think I can use Tuner Pro to hook up and see what my sensors are reading, but it looks like I'll have to pay for the RT version if I want to data-log.
Too bad I can't just use Win-ALDL, it looks so much easier!
-Ben
You're on the right track with getting the cable and software up and running. They make troublehsooting problems like these much simpler and you end up not spending a ton throwing parts at it.
Check out the TTS Datamaster software. You get 20 datalogging runs and unlimited live monitoring for free. It's really good software IMO.
As far as your specific problem, my truck was exhibiting roughly the same symptoms a couple years ago - it was a faulty idle air control (IAC) valve.
Check out the TTS Datamaster software. You get 20 datalogging runs and unlimited live monitoring for free. It's really good software IMO.
As far as your specific problem, my truck was exhibiting roughly the same symptoms a couple years ago - it was a faulty idle air control (IAC) valve.
Realized last night that I need a diode now.
Back to Radio Shack.
I'll try TTS Datamaster too. Time to dust off the old laptop.
Back to Radio Shack.
I'll try TTS Datamaster too. Time to dust off the old laptop.
OK, through some miracles, I got the circuit built and I got the laptop running again (sort-of)
I started the truck up and got Tuner Pro to actually read the data while it was running.
MAP showed about 4.8v at startup and was running about 1.15v at idle in the garage. I switched over to the new MAP sensor and the readings were almost identical. Now I'm not sure if the MAP was the problem or not. I suppose it always could have been an intermittent problem..... time will tell. I cleared the ECM and put the truck back together.
From what I can tell, most things look like they are functioning. The true RPMs are trending to follow the desired RPMS. I can watch the IAC change slightly and the RPMs fall right in line. This leads me to think the IAC is working.
TPS is at .55v at idle. Pushing down gives a nice ramp up to about 4.8v and 100%.
The O2 sensor is bouncing back and forth from about 800mv to 50 mv as it tries to regulate itself in closed loop. It appears to be working. The BLM values are still low, but the INT are looking close to 128. The readout said the truck started in OPEN mode and went to CLOSED as it warmed up.
I checked everywhere for vacuum leaks and didn't find any.
I'm not sure what else to look for here. I'll run the data logger as I drive it around now and see if it stalls. Hopefully I'll be logging when/if it does.
I started the truck up and got Tuner Pro to actually read the data while it was running.
MAP showed about 4.8v at startup and was running about 1.15v at idle in the garage. I switched over to the new MAP sensor and the readings were almost identical. Now I'm not sure if the MAP was the problem or not. I suppose it always could have been an intermittent problem..... time will tell. I cleared the ECM and put the truck back together.
From what I can tell, most things look like they are functioning. The true RPMs are trending to follow the desired RPMS. I can watch the IAC change slightly and the RPMs fall right in line. This leads me to think the IAC is working.
TPS is at .55v at idle. Pushing down gives a nice ramp up to about 4.8v and 100%.
The O2 sensor is bouncing back and forth from about 800mv to 50 mv as it tries to regulate itself in closed loop. It appears to be working. The BLM values are still low, but the INT are looking close to 128. The readout said the truck started in OPEN mode and went to CLOSED as it warmed up.
I checked everywhere for vacuum leaks and didn't find any.
I'm not sure what else to look for here. I'll run the data logger as I drive it around now and see if it stalls. Hopefully I'll be logging when/if it does.
Well, the MAP sensor didn't fix the problem. It was worth a shot I suppose.
Now it's also 'bogging down' or hesitating in traffic. I've got a little bit more to do to get the computer reliably logging. I'll try to get it up and running tomorrow and get the truck to do it's tricks while the computer is watching.
I've also got a fuel pressure gauge on order to get here Tuesday. I wanted to do the cool TBI adapter fitting with a permanent gauge, but it was just getting way too pricey for me.
Sooner or later I'll get this one nailed down.
Now it's also 'bogging down' or hesitating in traffic. I've got a little bit more to do to get the computer reliably logging. I'll try to get it up and running tomorrow and get the truck to do it's tricks while the computer is watching.
I've also got a fuel pressure gauge on order to get here Tuesday. I wanted to do the cool TBI adapter fitting with a permanent gauge, but it was just getting way too pricey for me.
Sooner or later I'll get this one nailed down.
Another update in the troubleshooting process. I got some time to spend with the truck yesterday and this is what I found:
Fuel Pressure:
Tested the fuel pressure on both sides of the Fuel Filter. Both read 12.5 PSI. I clamped the return line and the pressure went up to about 15.5. I shut the engine off and the line held pressure at 15.5 until I released the clamp and then it fell back down.
From what I can gather, this means that the Fuel pump is OK.
I replaed the EGR valve with a Delco part about 1.5 years ago, so I am assuming it is OK. I checked the EGR solenoid with the engine off and it held a vacuum (Not leaking)
Checked the ingnition coil: All resistances check out OK.
Checked the Pick-up coil: All resistances checked out OK.
Checked the ground on the distributor - OK.
Changed the ignition module out with a known good one from my pile. Applied dielectric grease to the bottom before installation.
Cleaned up the grounds on the ignition coil and reinstalled it.
Checked all plug/coil wires. All appear good. (Replaced recently)
I've got it back together now and will be driving it for a few days to see if it keeps up with the tricks.
I've been trying to log with TunerPro, but I can only get data at idle. As soon as I hit the gas, the error count skyrockets and it quits logging. I'm not sure what the problem is yet. Maybe in my connections, maybe in the communication with the ECM? I'll be downloading Datamaster this weekend and trying that one to see what it does.
So after all this screwing around, all I've done is change the MAP (which didn't fix it), cleaned the grounds on the ignition coil, and swapped out the ignition module. I'm crossing my fingers that it goes away, but my hopes are not high.......
I'll post back when I know more.
As usual, any thoughts/suggestions are more than welcome.
-Ben
Fuel Pressure:
Tested the fuel pressure on both sides of the Fuel Filter. Both read 12.5 PSI. I clamped the return line and the pressure went up to about 15.5. I shut the engine off and the line held pressure at 15.5 until I released the clamp and then it fell back down.
From what I can gather, this means that the Fuel pump is OK.
I replaed the EGR valve with a Delco part about 1.5 years ago, so I am assuming it is OK. I checked the EGR solenoid with the engine off and it held a vacuum (Not leaking)
Checked the ingnition coil: All resistances check out OK.
Checked the Pick-up coil: All resistances checked out OK.
Checked the ground on the distributor - OK.
Changed the ignition module out with a known good one from my pile. Applied dielectric grease to the bottom before installation.
Cleaned up the grounds on the ignition coil and reinstalled it.
Checked all plug/coil wires. All appear good. (Replaced recently)
I've got it back together now and will be driving it for a few days to see if it keeps up with the tricks.
I've been trying to log with TunerPro, but I can only get data at idle. As soon as I hit the gas, the error count skyrockets and it quits logging. I'm not sure what the problem is yet. Maybe in my connections, maybe in the communication with the ECM? I'll be downloading Datamaster this weekend and trying that one to see what it does.
So after all this screwing around, all I've done is change the MAP (which didn't fix it), cleaned the grounds on the ignition coil, and swapped out the ignition module. I'm crossing my fingers that it goes away, but my hopes are not high.......
I'll post back when I know more.
As usual, any thoughts/suggestions are more than welcome.
-Ben
I don't want to jinx it, but it's been 4 or 5 days now and the problem has not re-surfaced.
If this is truly fixed, it was either the Ignition Control Module or the Ignition coil ground that made the difference.
I'll give it another few days and if I'm still good I'll swap the old ignition module back in to see if the problem returns.
-Ben
If this is truly fixed, it was either the Ignition Control Module or the Ignition coil ground that made the difference.
I'll give it another few days and if I'm still good I'll swap the old ignition module back in to see if the problem returns.
-Ben
Looks like I jinxed it.
The truck ran great for a month or so. Just this last weekend it started sputtering on the way home. No problem at lights, etc when it was idling, but under load it would sputter and hesitate. Some shuddering while cruising down the freeway. (Felt like it was 'missing' or 'retarded')
Got her home (barely) and finally looked at it today. Checked all the wires, cap, rotor, etc. Ignition coil checks out OK. On a whim I changed the ignition module back again to see if that would make a difference.
Took it out for a test drive and still sputtering/shuddering under any kind of load. Sounds fine at Idle.
About 1 mile into the test drive it sputtered and died. Had to have my wife come out and pull me home.
I only had a few minutes, but I did learn these few things:
Fuel pump is making a 'running' sound when the switch is turned on. (Voltage is getting to it)
ECM flashes 12, but no codes. I take this to mean it is still alive. Is that a correct assumption?
Tried to start her with starting fluid and NOTHING. Just cranked and cranked, didn't catch. I take this to mean no spark is my problem.
I'm starting to wonder if the pick-up coil might have been bad and by 'testing' it a month ago I inadvertently jarred it into working again and it took a month for it to finally fail. (Is this too far fetched?)
I've got to believe the ignition module is good since switching them made no difference.
The ignition coil checks out find with the multi-meter.
Cap/rotor/wires are fine.
What the heck else is left for me to check? Could the ESC be bad?... should I disconnect it and see if it runs? Other than my far-fetched pick-up coil idea, I'm running out of options........
Thoughts?
-Ben
The truck ran great for a month or so. Just this last weekend it started sputtering on the way home. No problem at lights, etc when it was idling, but under load it would sputter and hesitate. Some shuddering while cruising down the freeway. (Felt like it was 'missing' or 'retarded')
Got her home (barely) and finally looked at it today. Checked all the wires, cap, rotor, etc. Ignition coil checks out OK. On a whim I changed the ignition module back again to see if that would make a difference.
Took it out for a test drive and still sputtering/shuddering under any kind of load. Sounds fine at Idle.
About 1 mile into the test drive it sputtered and died. Had to have my wife come out and pull me home.
I only had a few minutes, but I did learn these few things:
Fuel pump is making a 'running' sound when the switch is turned on. (Voltage is getting to it)
ECM flashes 12, but no codes. I take this to mean it is still alive. Is that a correct assumption?
Tried to start her with starting fluid and NOTHING. Just cranked and cranked, didn't catch. I take this to mean no spark is my problem.
I'm starting to wonder if the pick-up coil might have been bad and by 'testing' it a month ago I inadvertently jarred it into working again and it took a month for it to finally fail. (Is this too far fetched?)
I've got to believe the ignition module is good since switching them made no difference.
The ignition coil checks out find with the multi-meter.
Cap/rotor/wires are fine.
What the heck else is left for me to check? Could the ESC be bad?... should I disconnect it and see if it runs? Other than my far-fetched pick-up coil idea, I'm running out of options........
Thoughts?
-Ben
Oh, one more thing
I'll check it again tomorrow, but I SWEAR there was no fuel coming out of the injectors when I tried to crank it. That's why I tried the starting fluid and was shocked when it didn't catch.
Is there anything else I might be missing here that would cause the truck not to at least sputter on starting fluid?
Thanks,
-Ben
I'll check it again tomorrow, but I SWEAR there was no fuel coming out of the injectors when I tried to crank it. That's why I tried the starting fluid and was shocked when it didn't catch.
Is there anything else I might be missing here that would cause the truck not to at least sputter on starting fluid?
Thanks,
-Ben
To continue my conversation with myself.....
Reading up online it said that if a pickup coil is bad it might not give the ECM the signal it needs to fire the injectors. That would explain not seeing any gas in the TB.
Then I read that sometimes if you let the truck sit for a while it will re-start once it cools off.
Just went out and tried it. The truck fired up like everything was normal.
EDIT: I didn't change anything from when it was not starting several hours ago. I just walked out and turned the key.
In my mind, this means I've got a bad pick-up coil. Does that make sense to you guys?
Let me know. I'm going to crash for the night and re-check this in the AM before I go buy parts.
-Ben
Reading up online it said that if a pickup coil is bad it might not give the ECM the signal it needs to fire the injectors. That would explain not seeing any gas in the TB.
Then I read that sometimes if you let the truck sit for a while it will re-start once it cools off.
Just went out and tried it. The truck fired up like everything was normal.
EDIT: I didn't change anything from when it was not starting several hours ago. I just walked out and turned the key.
In my mind, this means I've got a bad pick-up coil. Does that make sense to you guys?
Let me know. I'm going to crash for the night and re-check this in the AM before I go buy parts.
-Ben
If you've already put a NEW ignition module in and it is still doing it then YES the pick-up coil is probably the culprit. I always like to change the pick-up coil AND ignition module at the same time.
I'll admit that it wasn't NEW but it was known to be good.
(I replaced it preventatively 80,000 miles ago for a trip up into Quebec for Caribou hunting and kept it around as my backup).
I think I'm going to pull the dizzy today and go through it while replacing the pickup coil.
(I replaced it preventatively 80,000 miles ago for a trip up into Quebec for Caribou hunting and kept it around as my backup).
I think I'm going to pull the dizzy today and go through it while replacing the pickup coil.
Did you put a liberal amount of the die electric grease on the back of the module before you installed it? If there isn't enough the heat will kill a module quickly. Also the oils from your hands will make them go bad so be careful to avoid touching the backside as much as possible.
I did grease it liberally.
Good call on the skin oil, I didn't know that one.
I may replace that too when I do the pickup coil. They aren't that expensive for all the irritation this is causing.
-Ben
Good call on the skin oil, I didn't know that one.
I may replace that too when I do the pickup coil. They aren't that expensive for all the irritation this is causing.
-Ben
Thunder
3/4 ton status
After reading theis thread I think it is your pick up coil. Did you check Resistance thru it? Pull the pick up coil plug off the module and check ohms between the wires. Should be between 500 and 1500 ohms. be sure to check when the engine is fully warmed up. If out of specs the PU coil is bad.
