Help fuel injection issues
Drifting
Joined: Aug 2010
Posts: 1,704
Likes: 8
we assume you have set all basic stuff to golden point ,so now, after adjusting your Maf wire,i would suggest to datalog the car,only way to see what actually is going on in terms of fuel trim.You need an aldl obd1 cable and tuner pro rt connected.when you have an idle going up and down about 500 rpm usually is an ECM compensating idle routine and opening and closing the IAC.This is basically related to your engine mods.Does the car do this up and down in open loop or closed loop,usually they start to do up and down in closed loop when they start an active fueling computation based on O2 sensor ,Maf and CTS sensor feedback.Tuner pro shows you BLM and Integrator numbers that actually go lean in the 128>160 range and rich in the 128<108 range.Integrator is equivalent to modern obd2 short fuel trim,BLm learning block module are the Long fuel trim.
Last edited by tunedport85inject; Feb 20, 2017 at 03:20 PM.
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
On mine, the 2 relays behind the battery for the MAF have tye same exact plug but the relays and the plugs are wired differently. They were swapped. Im pretty sure the lot i bought it from knew there was an issue but couldnt figure it out. It seems that it criss wired something that affected the output from the sensor. Funny thing was it didnt mess with everything. I went round and round with the scan tool because i couldnt get it to connect so i figured my ECM was bad. A buddy had an early 86 and the scan tool worked fine. I could put my ECM in his car and it worked fine. I put his ecm in mine and same story but i could connect to it with the scan tool. His ECM was actually different inside but the plugs matched up. Finally i tryed setting the scan tool for an 87 and it connected. Go figure, i must have a really late 86.
Along the way i did find issues with several places where the insulation at various plugs had receeded back from the plug and were potentially shorting out.
I am assuming this problem showed up on yours all by itself but it does bear asking if any work was done recently.
Either way, i would inspect the wiring carefully.
I went as far a ohming out stuff from the computer to the sensors. When i hit the burn off circuit things got wierd and led me to the relays, which i tested good but never imagined the plugs could be swapped.
Along the way i did find issues with several places where the insulation at various plugs had receeded back from the plug and were potentially shorting out.
I am assuming this problem showed up on yours all by itself but it does bear asking if any work was done recently.
Either way, i would inspect the wiring carefully.
I went as far a ohming out stuff from the computer to the sensors. When i hit the burn off circuit things got wierd and led me to the relays, which i tested good but never imagined the plugs could be swapped.
MAF Relays- drivers side, behind battery, visible without removing battery. I removed the fender skirt and the battery and then the relays. Both relays are identical- 5 pins.
The right relay is the MAF Sensor Power Relay and uses all 5 of the pins. On FSM page 6E3-A-2, this is item #17.
The left relay is the MAF Sensor Burn Off Relay, and uses only 4 of the pins. On FSM page 6E3-A-2, this is item #18.
Both OEM Relays have a circuit diagram on the cover which is identical.
The ACDelco replacement is listed by ACDelco as a “Multi-Purpose Relay” #15-8240. Rockauto sells this part for about $12. Rockauto also lists GM# 14089936 and 14103304.
These relays are interchangeable since they are 100% identical.
So, if the connectors are accidentally put on the wrong relay, no problems can be caused.
Instructor
Joined: Oct 2015
Posts: 134
Likes: 6
From: Osceola WI
Yea i read somewhere that they changed those which is a good thing, it never should have been the way mine was. I have considered rewiring mine so that particular problem cannot happen again either.
Well good luck
Well good luck
