Issue with hesitation on cold start

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babywag
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Joined: Fri Jun 08, 2012 7:29 pm
Location: Land of Fruit Loops & Coconuts

Re: Issue with hesitation on cold start

Post by babywag »

It's not difficult to mod a regulator.
https://www.thirdgen.org/tbi-afpr/
-Tony
'88 GW (aka Babywag)

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Theodore
Posts: 377
Joined: Tue Sep 04, 2018 5:26 pm
Location: East Tennessee

Re: Issue with hesitation on cold start

Post by Theodore »

It's been a few days since i've been able to provide an update; life got in the way - had to jump over & work on the house to get some things ready for winter. Have been testing the Jeep in between. Here's what i've done & where we are. All of the logs are pulled starting with the
engine cold.

I've not been able to get a copy of the .bin from AFI (will likely have to get a Moates device to read it myself), but did get some advice to swap the O2, reset IAC to ~10, & TPS to .74V. Base idle is 750rpm.

First, i swapped out the O2 sensor, and ran over the mountain & pulled the log. i really couldn't tell any difference, either hesitation when cold in the driveway, or the miss on the highway. Log from this is named "After O2 Sensor Swap".

Next, I reset the base idle/IAC/TPS according to AFI's recommendations to 750/IAC=14/TPS=.74V, and pulled a log: "AfterIACsetTo14-TPSsetTo74". While the engine seemed to start better, the miss on the highway was really bad; am usually able to climb the mountain at 70, with throttle to spare; this time, the engine was missing so bad above 60, i let off at 65, deeming this change a failure.

Next, I reset the base idle/IAC/TPS to 750/IAC=10/TPS=.59V, and pulled a log: "AfterIACsetTo10-TPSsetTo.59V". The engine started OK, with minimal hesitation, but the miss on the highway was back to normal. Power returned to being able to climb at 70mph, with throttle to spare, with the miss returning to normal "accelerating at 70/let off/coast to 60 & got back in it...

Next, it seemed it was time to take a look at fuel pressure. I have a fuel pressure gauge plumbed into the input runner, which consistently shows 12lbs. Babywag, i saw your mention of adjusting fuel pressure via regulator on thirdgen.org; i also came across this article on
binderplanet, showing that the pressure can be adjusted by turning the 'knob' on the bottom of the regulator "can". I used this method:
http://www.binderplanet.com/forums/inde ... ure.50514/

I ran several tests at various fuel pressures grabbing logs every time, and while raising the pressure seemed to make starting better, reducing cold start hesitation at first acceleration, it seemed to make the miss worse on the highway at speed. Have attached logs for FP=14lbs & 13lbs; am currently sitting at FP=12.x lbs, about 1 turn above where we started - Jeep starts better than ever, still has a slight miss, with first acceleration out of the driveway the best i've seen to date. I've not had a chance to go out for a test run over the mountain as yet.

One thing i notice across all of the logs, is the O2 sensor is often dropping well below 100, and sometimes to 0. From earlier pics, the O2 sensor is mounted in the drivers side exhaust pipe 10 inches below the manifold. Thinking out loud, am wondering if there's a bad electrical connection at the ECM harness, at the O2 sensor wire? Will take at that look today.

Other thoughts:
1) Run a test, data log FP=12.x lbs & post
2) Check the O2 sensor wire for a bad connection at ECM connector
3) Pull the injectors & send them off for flow bench & cleaning
4) Pending results from #3, order a chip reader from Moates & pull a copy of the .bin to see what the actual settings are

? - do you see anything in the logs that lead you otherwise?
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1990 Grand Wagoneer - "Theodore" - AMC 360, fuel-injected, TF727, NP229 - Sand Metallic - restoring to stock - Build Thread
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