90 Grand Wagoneer - chasing cold start hesitation/rough idle

[Theodore]

Am looking for help w/an issue i've been chasing since we owned the Wagoneer: rough idle/hesitationat cold start, and hesitation/backfire - when running at highway speed & letting off the throttle, coasting a bit, then getting back in it.


Jeep is a bit of a Frankenstein, with parts making quite a long-strange trip before being mated together in East Tennessee. From what ive been able to piece together, the AMC 360 engine was in a Grand Wagoneer (not sure the year), when AFI's EFI (1227747 ECM) were installed in 2006 in NJ. The engine & EFI was eventually sold to a Jeep junkyard in NC 3-4 years back (not sure what happened to the original Wagoneer), and subsequently sold to the previous owner of my Jeep, to mate with a body he'd found in Atlanta. To add to the mystery, from the high elevation sticker under the hood & the lack of rust, am thinking the body was originally out West somewhere.


With that out the way, over the last couple weeks, have dug in & fixed a myriad of issues relating to voltage drop & the ECM reading low battery voltage (~12.5V). By performing voltage drop tests on the 3 power-related ECM connections (pins A6, B1, & C16), tracing wires, removing short splices of wire & re-splicing, cleaning grounds, cleaning electrical connections with DeoxIT D100 contact cleaner, finding/fixing a cracked/corroded fuse, etc., i've seen battery voltage reported by the ECM rise from 12.5V to 14.2V, resulting in a better running, quieter engine. Overall, it's never run better.


But, i'm still chasing the:
- hesitation at cold start
- intermittent dying when going from park to drive
- backfire at speed problem,
that it's had since day one.


Over the last few days, i've noticed that when comparing voltage measured by back-probing the ECM connections w/multimeter vs. what the ECM reports, that there's a .2-.4V variance - the ECM reporting lower. Am wondering if i have a bad connection with one of the pin connectors in the ECM harness?


Here's the car we're working on:



Cracked fuse worth ~1V! Battery voltage reported by ECM jumped from 13.2 to 14.2.



ALDLdroid dashboard after the wiring cleanup effort - Battery Voltage - lower right.



Attached are the latest set of data logs, would appreciate your taking a look & see if anything jumps out. One thing i notice in the logs is voltage drops the longer the engine runs... So far, i'm only driving it in a 6-10 mile loop that includes in-town & highway driving, so am wondering how far it would continue to drop if i drove longer/further? Am planning on taking it out later on this weekend, for a longer test drive & see what happens.


Right now, the ECM is in mounted in a box under the hood, on the driver's fender where the rear window washer bottle should be. Given the hacked up nature of the EFI harness, am planning on getting a new one & moving the ECM to inside the Jeep - just wanted to get it running properly first. Am wondering, given all the trials/tribulations dealing w/the existing harness, whether i might be better off, to get a new harness & start over?


Wondering: could engine heat be affecting measured voltage? Such that, we could expect an improvement once i move the ECM into the cabin?

Thanks.

[dave w]

Does the Wagoneer have a Vehicle Speed Sensor (VSS)?

dave w

[Theodore]

Does the Wagoneer have a Vehicle Speed Sensor (VSS)?

dave w

Hey, Dave, honestly, I don’t know. Reading thru the AFI owners manual, VSS shows as optional. May have to do some wire tracing to figure it out. Fortunately I found the ECM pin-out diagrams elsewhere on the site to give me an idea of where to start.

[ony]

jeeps an guns use to have jeeps,might contact him

[Theodore]

jeeps an guns use to have jeeps,might contact him

Thanks, ony - will do. Am thinking he's who took a set of Wagoneer leaf springs i had to give-away a few months back.


BTW, a couple aspects worth knowing, is: IAC, TPS, & MAF are new. The EGR valve is there, but no vacuum line is connected. EGR Vacuum port was uncapped, when i got the Jeep; i capped it a few months back when i replaced all vacuum lines to prevent dirt from getting in it. The vacuum switch that the EGR vacuum line would connect to is missing.

For additional context:
- initial timing is set to 10 degrees BTDC
- used bluetooth OBD1 scanner, with ALDLdroid to set up:
---- base idle (650-700 warm), IAC & TPS
---- initial setup for IAC
---- initial setup for TPS
- fuel pressure shows 12 lbs - steady
- fuel filter is relatively new
- not done anything w/o2 sensor

[dave w]

The factory specification for most TBI engines is ZERO degrees BTDC.

The VSS has caused some debate on the board over the years. Most members agree it not NECESSARY. Most members agree it NICE to have. Some members have reported unexpected stalling was NICELY eliminated with adding a VSS.

dave w

[tayto]

whatever you set your initial to must be reflected in the bin. while most stock TBIs are 0* initial, i found 10* worked well with faster cold and hot starting.