16197427 PCM woes......

[billygoat]

First post, here, I lurk a lot, and hang out on another forum with a member here.

Here is my situation, I just got an AMC 401 running in a J20 with a 4L80E tranny all controlled by a 16197427 PCM.
Finnaly got it all working and on a short test drive the engine sputtered, shifted into 2nd, and I lost my laptop reading the PCM, and the check engine light was flickering.
I had a 2nd PCM with me so I hooked it up, same issue, so I limped home, once there i discovered the MAP wire had melted to the EGR valve, I fixed that, and everything acts the same...

The CEL is not really a flashing, it is more like a flicker, like a bulb that is loose.
jumper for diagnostic mode, and CEL stays on solid then.
Neither my laptop, or code reader will see the PCM.
I checked everything I could think of, check for grounding out on all the connecters and between the pins and nothing showed a problem, I have a pin out that shows what each wire should have key on, and they are all good.

So any ideas? things to check? I am worried I fried both PCM (2 more on the way), the chips still read in my programmer, so they are ok, I did open up 1 PCM, no visual burns, but with a printed board I know you don't always see them.

[dave w]

I'm wanting to make sure I understand the PCM configuration your using:
The 16197427 PCM is being used to control the 4L80E only?
The 16197427 PCM is being used to control both the 4L80E and a TBI conversion to the ACM 401?

In either case, I would work on one problem at a time. I would want to have the diagnostics, scan tool or data logging software, working first and foremost. I've built a few 16197427 PCM wiring harness. Before I but the harness into a vehicle, I test the harness by that having all power connections powered up and the distributor turning with an electric motor to supply the PCM with the ENGINE is running signal. I connect the ALDL cable from my Laptop to the ALDL connector in the wiring harness and use TunerPro RT data logging software to verify the sensors are working. I use a hand vacuum pump on the MAP sensor and and watch for changes in the MAP sensor readings. I open and close the throttle to watch what the TPS voltage is doing. I change the RPM on the electric motor spinning the distributor to see changes in the RPM. I'm thinking a similar testing technique could be done with a harness already in the vehicle, except use a spare distributor to supply the PCM with the ENGINE is running signal.

dave w

[EagleMark]

Flickering CEL is usually the chip programmed wrong or became loose. Did you program the chip with correct offsets? Have to get that right so CEL at key on, comes on, blinks once and stays on, then when started goes off. Stock Memcal should work correctly till started then may find DTC...

[Six_Shooter]

Like Mark said, check the EPROM, the PCM is not reading the EPROM or emulator correctly. Cheack and re-seat EPROM and or MEMCAL, then re-check CEL finction at key on.

[billygoat]

the PCM controls all, and to back up, it was engine only with the 360, then I went 401 (basic program change) and the 4L80E. Took me a few tries to get the 4L80E to shift, but the engine was fine.
Then the map wire fried, and presumably that is when I lost the serial data, and have the funky flickering CEL
I have a log recording of when it lost it, but all you see is lost of connection, then it gets connection then loses it, never to come back again. Nothing looks odd on the couple samples between losses, not a single error code.

My problem is without being able to see any info from the computer I have dead in the water to analyze anything.

I guess I am looking for any tests I can run with an multimeter to test wiring/sensors?

I left the MAP unplugged, thinking it could be fried - should I unplug everything and check for continuity to ground and make sure nothing is???
I want to minimize the risk of damaging a replacement PCM if that is what happened to my current units???
The truck did run in limp home mode, so the PCM has to work somewhat, the fuel pump ran and the injectors fired at least, can not say if it added any spark advance.

[billygoat]

Like Mark said, check the EPROM, the PCM is not reading the EPROM or emulator correctly. Cheack and re-seat EPROM and or MEMCAL, then re-check CEL finction at key on.

done that, even switch the MEMCALs between the 2 PCM's, even put the chips in my programer and verified they are good.
No change, even left the chip out, then the CEL stays on solid

[EagleMark]

I think you found the answer and are looking for a confirmation... was working and MAP wired fried and you lost PCM, put in new PCM without knowing of fried wire and it went bad from fried MAP sensor wire? I'd fix the wire and check the MAP sensor and plug in another PCM. and check fuses, seems a fuse should blow if this happens? But fuse is before PCM so not sure what would happen to PCM?

[billygoat]

Just a thought, what is bare minimum the PCM needs so I can hook it to my laptop, I have another set of PCM plugs, and pretty sure another ALDL connector, so can I hot wire to the grounds and power ins, then I should be able to at least connect to it?
Then I at least know if the issue is in the PCM or with the rest of the system....

[EagleMark]

so can I hot wire to the grounds and power ins, then I should be able to at least connect to it?

I think we found the issue!

OK we will take that as a typo... couple system powers and a couple system grounds, CEL and serial data should do it. Check the wiring diagrams.
http://www.gearhead-efi.com/Fuel-Inj...Information-OD

[billygoat]

"Hot wire" as in I run the neg to neg and pos to pos on a jump it pack, not all get a power....

Looking for a way to get a bench test on the PCM with out a complete system, if with power to it the laptop should connect, that I know the PCM is ok and it is an issue with the rest of the system, or if the PCM does not connect, then I trust I cover the bases in the truck and plug a replacement unit in.

I checked EVERY fuse in the truck, none blew, I would expect that with a short, 1 would have.
The base harness is a Howell kit for an 1227747 ecm repinned to the PCM

Like I said, I drove the truck a good 6 months or more with the PCM before the engine/tranny swap.
I should explain myself better I guess, on the other forum the usual people are use to my truncated explanations.
sorry for any confusion

[EagleMark]

No confusion, I understood but it sure looked funny!

Yes it will work to see if CEL works properly and if serial data is coming through. Bench build the extra PCM plugs, have to look at wiring diagrams but should be a couple Batt power, one Ign power, couple system grounds, serial data wire and I think a ground in ALDL port with serial wire. Not to hard... don't need all the other sensors and stuff hooked up for this. I have a couple bench flash setups for LT1 and LS1 PCMs like this and CEL works and serial data works.

[dave w]

"Hot wire" as in I run the neg to neg and pos to pos on a jump it pack, not all get a power....

Looking for a way to get a bench test on the PCM with out a complete system, if with power to it the laptop should connect, that I know the PCM is ok and it is an issue with the rest of the system, or if the PCM does not connect, then I trust I cover the bases in the truck and plug a replacement unit in.

I checked EVERY fuse in the truck, none blew, I would expect that with a short, 1 would have.
The base harness is a Howell kit for an 1227747 ecm repinned to the PCM

Like I said, I drove the truck a good 6 months or more with the PCM before the engine/tranny swap.
I should explain myself better I guess, on the other forum the usual people are use to my truncated explanations.
sorry for any confusion

One idea I have is to unplug all the sensors and transmission plug from the PCM. Leave the power, ground, CEL, and ALDL connections to the PCM and see if CEL lights steady when the ignition switch is turned on. Then add one sensor connector at a time a see if the ALDL data is working? Maybe when you plug in one of the sensors or other connectors, the CEL will start flashing again?

dave w

[billygoat]

Excellent - thanks both of you.
I will bench test the PCM, and if it "works" I put it in the truck and connect 1 sensor at a time and see what freaks it out.
Even if the PCM fails, I will probably put the replacement in and connect 1 sensor at a time, after I test all the wires for a short again - no need to cook another PCM if I did already....

[1project2many]

The pcm can handle the MAP wires being connected to ground. There are three wires: Signal, 5V and ground. If 5V is grounded then the 5V line shared between MAP and CTS or TPS goes to zero and multiple sensors give wrong readings. If signal is grounded MAP signal voltage goes to zero and pcm flags a code. And if ground is grounded? You have redundant grounds.

I've run into chips which will read correctly in a programmer time and time again but are not right when connected to a memcal. Maybe it's an internal short and the ECM/PCM 5V signal is on the high side of 5V which bridges the short? Maybe there's an open? Maybe the logic of the programmer and software is better able to interpret a voltage "in the middle" of high and low than the pcm? Lotsa maybes but the best answer is to find another chip / memcal and try again. Watch out for static shocks which can cause exactly this issue. Hold onto the metal PCM case before pulling the chip to help ground yourself if necessary. If you have any stock memcals that are unmolested try a basic check: Key on, watch check engine light. Light should turn on briefly, turn off briefly, then light and stay lit.

[JeepsAndGuns]

I'm a little curious to know why the wires melted together. Did they melt because they got next to a hot exhaust pipe and melted. Or did they heat up and melt like a short circuit (let the magic smoke out)