brutalis

iTrader: (3)

For reference, '98 T/A, converted to 99+ PCM, H/C/I/E/etc, !EGR, !AIR, !EVAP, !R02S, Frost tune to account for all of this except !EVAP.

I thought I was getting close to a running car this past week. I installed my custom built engine harness to use the 99+ PCM and relocate into the cabin, everything seemed to be going well. The car would start right up, idle fine, rev smoothly, all that jazz, but was throwing a couple codes. If I recall correctly:
P0107 - MAP sensor low voltage
P0445,P0449 - not sure if it was those two but both were due to removing EVAP system, nbd
P0452 - fuel tank pressure sensor low voltage
P1635 - 5V ref circuit 1
P1639 - 5V ref circuit 2

I ignored the 2 for the evap, since it was just deleted, 1635 and 107 are related (5V ref 1 contains MAP sensor), same with 1639 and 452. After running through the troubleshooting tree to confirm it was those 2 sensors, I reconnected the fuel tank pressure sensor (I had left it out intentionally since it is only used for EVAP), then discovered 2 wires at the MAP sensor connector were switched and corrected them.

"Good, that should solve my problems, right?" ...wrong, now the car won't start at all. First attempt it kinda started and ran rough for about a second, then died, then would halfway attempt to start (1 or 2 cylinders firing) for a couple tries after that, then nothing. So I undid the two things I changed, still nothing. Tried disconnecting the battery (for 24 hours) to let the PCM reset, still nothing. AFAIK, the only things that would keep it from starting like this would be VATS (which I think I had removed, and have never had problems with before), dead PCM (unlikely), or poor/no communication with the CKP sensor (the wiring for which I just debugged previously), so I'm running out of ideas.

TL;DR Car was running, made a couple minor wiring fixes to MAP sensor and fuel tank pressure sensor, now it won't start. HELP?

Jrclayton

Unhook the maf (dont take it off just unplug it) and see if it will fire then. If so then you found your issue. also your wiring "fixes" might have fried your old map sensor. have you looked at it to rule that out?

Jrclayton

Just posting this to update the number of responses so you know i updated my other reply.

chrysler kid

iTrader: (14)

My car did that when I installed the coil packs backwards. Make sure they are all correct 98's are tricky because there are no brackets and the drivers side the first coil is installed backwards.

Why did you want to swap out the ecm? the 98 would have held a tune for a head cam setup just fine, but be limited on your advanced settings and maps because of lack of memory. Plus I have yet to see a good write up on getting everything 100% functional

brutalis

iTrader: (3)

Jrclayton: I completely unplugged the MAP to rule it out. I know it can run that way because I had to idle it with the MAP unplugged when running through the diagnostic tree for the P1635.

chrysler kid: What do you mean by installed backwards? As long as it's wired correctly, it shouldn't matter how it's installed, right? As for switching the PCM, I did it because I managed to fry 3 of the '98 units (one of which had a tune on it) and couldn't figure out why, so I just decided to completely redo the engine harness. It's not 100% (no low oil light), but all the important components work just fine.

brutalis

iTrader: (3)

Updates from today's diagnostic testing:
The crank position sensor is good, the MAF isn't causing any problems, and the VATS circuit is performing as it should. When cranking, the fuel pressure stays up around 55-60psi. I don't seem to be getting any injector pulse from the PCM, but hard to be 100% sure with just a DMM. IGN and BATT sources at PCM are all good.

Based on this, the PCM should not be bad since the fuel pump seems to be running during cranking. The only weird anomaly that I could find was that the battery drained to about 8.5V with the ignition on for only about 15 minutes (no radio or accessories except maybe a dome light on) while I was testing.

The "crank but no start" diagnostic tree in my service manual is out of ideas, and so am I. Here's hoping somebody has a suggestion for me...

chrysler kid

iTrader: (14)

Have you performed a crank relearn on the new ECM?

brutalis

iTrader: (3)

...what? The ECM isn't new, the car has been running with it (off and on) for the past year or so.

brutalis

iTrader: (3)

Bump, any more suggestions? If it's warm enough this afternoon, I'm gonna try to take my test light out and confirm whether or not I have injector and coil pulses. If so, I'll honestly be excited to finally deal with a mechanical issue as opposed to electrical.

chrysler kid

iTrader: (14)

From your original post you had just done the conversion, just trying to trouble shoot

brutalis

iTrader: (3)

No, like I said, the car was running fine apart from the few codes listed.

I did go ahead and check for pulses, and I DO in fact have injector and coil pulses. I also confirmed (by disconnecting the line at the rail and putting it in a jug) that the fuel pump is running and pumping fuel. Then I bought a spark tester and confirmed that the coils are producing adequate voltage to create a spark. Spraying starter fluid down the TB didn't seem to have any effect, which makes me think bad fuel is not the culprit. That pretty much just leaves the spark plugs, which is all but confirmed by the fact that I couldn't get a spark outside the cylinder using the plug (at .045 gap) despite being able to do so at close to an inch using the tester. I cleaned up some TR6's I had laying around and I'm going to try installing them tonight to see if that does the trick before I go out and drop $50 on a new set.

brutalis

iTrader: (3)

Okay, so I replaced the sparkplugs, and it fired right up. That was easy. However, the P1635 and P1639 codes are still lingering, and it's running like crud once it warms up. I checked the TPS at the sensor, and it's fine (need to check at the PCM), and pulled the O2s and tested them with the blue wrench, they're perfectly fine. I'll go ahead and run through the diag tree again for the codes and see if that solves anything, but I'm starting to wonder if I don't have a mechanical problem.