90 Grand Wagoneer - chasing cold start hesitation/rough idle

[dave w]

Every project ultimately has to reach a decision; is good enough, really good enough or is there something better?

The ICM cannot be programmed to optimize the timing (Spark Advance).

See sample 1227747 timing table below. The 1227747 controls the Spark Advance via the ignition control module. 1227747 timing tables use a metric vacuum scale call Kilo-pascals (Kpa). WOT Kpa is 100 (kind of like- nearly Zero Hg), and coasting down a 3 mile long 10% grade is 10 Kpa (kind of like nearly 20 Hg). Cruising on a level grade at 70 MPH is usually between 50 Kpa to 70 Kpa.

Better just might be the ability to optimize the timing (Spark Advance) at WOT, Cruise, and Idle?

GM Ignition Module / ECM schematics are also attached below.

dave w

[Theodore]

Thanks for the background - this stuff's new to me. Reading/learning more everyday. Have read quite a bit that EFI systems are susceptible to flakiness due to bad electrical connections - i suspect a lot of the issues i've seen to date have been due to a large number of bad splices & the voltage drop associated with them, not to mention, a myriad of vacuum leaks i've found/fixed to date. When i started this journey last summer, ECM reported battery voltage was ~12.1-12.5V. Today, it ranges 13.8-14.2V. Am planning on replacing battery cables & adding an engine to frame ground strap this weekend pulling another log, and going from there. Am thinking a good next step is having a formal vacuum test run to ensure i have no leaks in intake or exhaust, then proceed to looking at the .bin for mismatches, like the EGR's enabled, but doesn't exist, wrong injectors defined, etc.

[In-Tech]

Thanks for the background - this stuff's new to me. Reading/learning more everyday. Have read quite a bit that EFI systems are susceptible to flakiness due to bad electrical connections - i suspect a lot of the issues i've seen to date have been due to a large number of bad splices & the voltage drop associated with them, not to mention, a myriad of vacuum leaks i've found/fixed to date. When i started this journey last summer, ECM reported battery voltage was ~12.1-12.5V. Today, it ranges 13.8-14.2V. Am planning on replacing battery cables & adding an engine to frame ground strap this weekend pulling another log, and going from there. Am thinking a good next step is having a formal vacuum test run to ensure i have no leaks in intake or exhaust, then proceed to looking at the .bin for mismatches, like the EGR's enabled, but doesn't exist, wrong injectors defined, etc.

Hello,
At any point in time this has all been new to all of us. Wiring issues have been around since there was wire, lol. In an automotive environment never be afraid to add more grounds, actually in most cases. Injector information is almost a waste of time these day, having an injector flow test machine has proven that to me so it goes back to "give it what it wants".

It really sounds like you are on your way to having a nice vehicle when you are finished.

[Theodore]

Making progress: Today, I swapped out battery cables & the ground strap. Turns out the ground strap was cracked/corroded & terminated on a painted metal surface on the frame. After sanding paint off to bare metal around the mounting bolt, and finishing the installation, we now have the highest voltage reported to date by the ECM, 14.5 (+.4V). At this point, we're up 2.3V from where we started, and finally to charging battery voltage.

Took the Jeep out for a test run, butt dyno says it's running better; am still seeing similar symptoms, though they aren't nearly as bad as before. Am planning on making another test run tomorrow without having had the battery disconnected & see what we have.

First of the week, am planning on having a smoke/vacuum test run to ensure no leaks, & contacting AFI to get a copy of the original .bin. Hopefully, someone here locally has a chip reader that can pull the .bin from the chip in the Jeep to compare.

? - re: injector flow bench - what kind of shop has that kind of thing? I called around to a few shops around here, and so far i've not been able to find one.

Attached today's data log, along with a few charts of key metrics.

RPM - noticed a roaming idle for 30 seconds at cold start, but it may be due to the battery cables having been disconnected. Am hoping this improves the more it's driven.


Battery Voltage (up .3-.4V from before)


IAC


O2 Sensor still shows quite a few measures below 100.


BLM (down a couple points from last run:135.83


INT


TPS


MAP

[Theodore]

Update: back from the shop & the smoke test: Was kinda hoping I had a vacuum/exhaust leak that would explain this, but as it turns out, I had found/fixed them all - passed the smoke test with flying colors. So, we appear solid on electrical, grounds, vacuum, and exhaust. Am wondering now, whether there’s a mismatch with the .bin & reality? Babywag at fsjnetwork recommenced having injectors pulled & cleaned/flowbenched, and EagleMark on the forum here, recommended MrInjector. I’ve not been able to find anyone locally that does this.

Am thinking next steps are: pull injectors & send off for cleaning, and pull the .bin for comparison, and see where we are.

Would converting to an adjustable fuel pressure regulator help here? Am running 12 lbs, where acceptable range is 9-13...

Any other ideas before we head down this path?

[dave w]

I also recommend Mr. Injector.

12 PSI is fine for TBI for a stock performance engine. Adjustable fuel pressure regulators are sometimes required for performance engines.

dave w