Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Work performed:
Cam and lifters changed was primary work done
Trunion upgrade , water pump, timing chain and gaskets associated.
Attempted initial fire up. Failed. Noticed main ground to cylinder from battery and injector harness not bolted connected. Also the MAF/iat was disconnected.
Next attempts had a little noise like trying to start but didn’t run.
May have been around this time we scanned for codes and had/have P0113 and u0100.
I only have the torque app or hp tuners for scanning.
P0113
Attempts to clear codes don’t work. Unplugging the maf/iat brought no change for iat code.
No other grounds found disconnected.
Looking at connection looked like had a liquid in between connectors.
This may have damaged the maf/iat but circuits appeared to be complete.
Tan to ecu has continuity
Tan/blk to ecu has continuity is 5v ref read 4.99v
IAT reads from torque app. Shows -40 to 302 when grounded or power connected.
Possibly just sensor issue?
U0100
At obd2 port 6 and 14 see 60 ohms everything connected.
Appear to be able to read data from ecu. Gauges on dash all show correctly.
I have been unable to find a fault as power and ground look to be present. Power train relay functions and power to subsequent fuses.
I’m at a loss as to what the problem is. I don’t see how it is and I don’t see how it isn’t the ecu?
Help is greatly appreciated and unfortunately need my truck up asap.
Planning to order an ecu tonight.
Thank you
Back probe iat and measure voltage then back probe pcm and measure voltage. Does voltage increase at pcm?
Now with sensor unplugged repeat tests. What do you have for readings on both legs of circuit.
Then repeat this test while wiggling wire harness or while looking at live data and see if it glitches. This could be a shorted to ref voltage issue or a break in wire and it's seeing a bias voltage reading and not getting a signal.
What module(s) we're reporting the u0100 or what module did it say it could not communicate with?
I have back probed both locations but I will again to confirm results.
As I recall when plugged in saw around 3.2v from 5v ref and I think around 2v at the tan wire return.
I don’t recall values at the ecu. After work I will run all those tests you suggested.
The only thing I have to go from is 0x7e8 for p0113 and 0x7eB for u0100. I don’t see otherwise where it tells me.
Thank you
Right. I didn't know if you were meaning it was the bcm or fscm stating the u0100 which I don't know that information.
PCM/ECM being the same thing i don't know what is not communicating as I appear to be reading the inputs through obd scanner.
Edit: also for time sake I have an ecm arriving tomorrow. I'd love to do any/all testing prior to prove out ecm or other issue.
I am just under a tight time constraints of needing the vehicle this weekend.
With your scanner setup where you scanning all modules or just ecm? If all modules then individually scan each module to tell which is reporting a no com with ecm then look at the data communication lines diagram and check wiring along the path and connectors for corrosion, wire chaffing broken wires.
Little update. Forgot keys so I couldn’t do suggested testing.
Previously performed testing for iat includes
Harness disconnected at maf/iat . Checked resistance from connector tan wire to ground. Result 0.5 ohms
Still disconnected. Ignition on sensor reads -40*f
Then jumper wire between iat 5v ref and ground. Result 302*f.
I then loaded each wire separately with ecu and maf/iat disconnected.
Using small jumper wires and a window motor. Without the motor in place I believe I had weak connections and was reading around 9.99v. Then with the motor in place it functioned and dropped the voltage I believe to 9.8v. This occurred on both wires from what I recall.
Lastly, when I disconnect the maf/iat from the sensor with KOEO I have a stabilatrak and traction control issues appear on the display in dash.
U0100
I had pulled abs module connection to check ohms on those tan and tan/blk wires for CAN. I believe it was 60 when connected and 120 when disconnected as would be expected.
Trying to recall what I can but will proceed with initial requested testing.
Just listing more that I had done prior to making my post.
Last edit: 3 years 1 week ago by theonlyQualk. Reason: Clarity
With positive lead at pcm tan/blk wire 5v ref and blk lead at tan wire sig return at iat I measure 5vdc. This stays whether connected or disconnected from iat.
Sensor seems to be dead now?
I did run checks as you mentioned and saw no difference between each wires voltage at iat or at ecm. No change in voltage upon shaking the harness.
When plugged into iat 5v ref dropped to 2.7v but corresponding was not seen at sig return.
I will say we had relays turned around it seems( compared to friends suburban 2012) and battery must of had a draw as it is pretty dead now. Have battery disconnected and charging.
We had one crank cycle where it sounded like it tried to start but through the intake.
Cleaned one ground on the frame. Didn't see any other grounds at the engine.
I added a ground from the negative cable at the cylinder head to the alternator bracket ground just to see if that helps.
Code scanner I borrowed only shows the p0113 code and is unable to separate between modules as far as I can tell. Either that or that is the only code present.
Latest update:
Borrowing a different code reader (obdwhiz) I can connect to ecm and seemingly fscm and tcm. Looks like ecm lost com with tcm.
Please take. A quick look at the secondary pcm ground on back of driver side cylinder head. There is a ground on each head.
I only see the the ground strap on back of the driver's head. None on passenger back.
Battery negative and a small ground front of passenger head.
I just found last night two ground wires on driver side of the block near the engine mount. Unbolted and cleaned up a little. Didn't break apart did show a little corrosion but otherwise intact.
I have not found other grounds on the engine.
Understood. I'll check that ground at the maf/iat connection with it connected and not connected. Not sure if that is the smaller ground wire I already have at the front of the passenger cylinder head.
Also RPd1125 that diagram looks much better than my all data ones lol.
I would as pre check before you continue with anything. Check both of these power feeds to the PCM. And the g103 ground to pcm at the pcm. At least make sure both of these fuses have power at both sides with voltmeter or power probe. Easy to check ground with power probe at pcm too
So a bit of an unfortunate thing has occurred.
Believe I mentioned i have fuel and spark. Sadly I didn't check compression at that time.
No compression.
Shop Air in cylinder and leaks out the intake. Even with the rocker off and tapping on the alve does not seal.
So either I messed up timing and bent valves or machine shop didn't do a good valve job....
I believe the u0100 likely isn't an issue. The p0113 is legit.
I appreciate the help on this but this likely won't run until after I return to town. Will update until it's fixed.
Just to close this out. I have a couple hundred miles on this now.
Issue was pushrods were too long. I mistakenly didn’t think I would need to change pushrods when switching to another gm cam.
I thought wrong. Bent all intake valves. Some more machine work, new pushrods, and new bolts it appears to run fine.
Lesson learned.
Thanks all
Topic Author
