1985 c4
Thread Starter
Heel & Toe
Joined: Oct 2024
Posts: 16
Likes: 3
1985 c4
At full temp. Loop open ,o2 mv443,intagrated 128,block learn128,iac 0,02 crosscounts 0,mat20,maf gm-sec 10 base power0.0af learned no.esc counter 0egr cyc.0, hi ps no, i am using a mt 2500 scanner is this narmal
Melting Slicks
Joined: Nov 2016
Posts: 2,253
Likes: 3,074
From: So Cal
2023 C4 of the Year Finalist - Unmodified
,iac 0
Many of the other parameters are correct for Open Loop operation, which the parameters shows it is in. The system should go into Closed Loop after a period of time after engine start, and Coolant temperature also rises to a minimum threshold. In Closed Loop, BLM, INT, Crosscounts, O2 Voltage, etc should show activity.
At full temp
Drifting
Joined: Sep 2022
Posts: 1,466
Likes: 382
From: Liberty, SC
2023 C4 of the Year Finalist - Unmodified
Hey there. To borrower the OPs thread and ask for a bit more info on this part of your response (it may help them too)
What other sensors are checked before it can get into Closed Loop? My 88 never goes into Closed - but using a voltmeter I've can see the voltage jumping up and down on the O2 wire.
What other sensors are checked before it can get into Closed Loop? My 88 never goes into Closed - but using a voltmeter I've can see the voltage jumping up and down on the O2 wire.
Melting Slicks
Joined: Nov 2016
Posts: 2,253
Likes: 3,074
From: So Cal
2023 C4 of the Year Finalist - Unmodified
Read the FSM section for Code 13. I just did. It is also the range of voltage fluctuation. If the voltage stays within about a 10th of .450, the ECM will consider the sensor "too cold", and won't enter Closed Loop.
Other than coolant temperature and time after engine start, I've never seen, nor does the FSM mention, any other parameters or inputs that must be met to enter Closed Loop. The conditions that set Code 13 are found while being driven, not at idle.
I had a 4.3 CPI that from time to time had a very annoying "hiccup" while at cruise speed. It drove me nuts, and would not respond to anything I replaced, which was a lot of things. At least a year into this crap, I was driving along the Interstate, it was really acting up, and I put the jumper in the ALDL and monitored Field Service Mode. It would cruise along in Closed Loop, then go into Open Loop, do the hiccup, and be back into Closed Loop. Every 60 seconds or so. There were never any codes. Ever. I replaced the O2 sensor (which had at least 150,000 miles on it) and no more hiccup. I now run O2 sensors a maximum of 75k before replacement.
O2 sensors can cause weird driveability issues.
Other than coolant temperature and time after engine start, I've never seen, nor does the FSM mention, any other parameters or inputs that must be met to enter Closed Loop. The conditions that set Code 13 are found while being driven, not at idle.
I had a 4.3 CPI that from time to time had a very annoying "hiccup" while at cruise speed. It drove me nuts, and would not respond to anything I replaced, which was a lot of things. At least a year into this crap, I was driving along the Interstate, it was really acting up, and I put the jumper in the ALDL and monitored Field Service Mode. It would cruise along in Closed Loop, then go into Open Loop, do the hiccup, and be back into Closed Loop. Every 60 seconds or so. There were never any codes. Ever. I replaced the O2 sensor (which had at least 150,000 miles on it) and no more hiccup. I now run O2 sensors a maximum of 75k before replacement.
O2 sensors can cause weird driveability issues.
Melting Slicks
Joined: Nov 2016
Posts: 2,253
Likes: 3,074
From: So Cal
2023 C4 of the Year Finalist - Unmodified
You can kind of check the ECM's ability to control the IAC by jumping the ALDL A&B (like pulling codes) turn key to RUN, and the IAC motor should be ticking rapidly continuously. If it isn't ticking, something isn't "right" but I don't know what to suggest to try if it doesn't tick.
Melting Slicks
Joined: Nov 2016
Posts: 2,253
Likes: 3,074
From: So Cal
2023 C4 of the Year Finalist - Unmodified
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
Oil Producer
Joined: Apr 2014
Posts: 9,368
Likes: 2,735
hooooold up
i commend you for scanning
the 85, and 84, can only be scanned in field test mode.
among other things, this mode forces the car to run at 1000rpm. the long and short of it, is that you cannot set the idle rpm / iac counts / tps positions while scanning due to this. example, you may want to tune your iac to be 50 at idle. U cant, on 85 and 84, because you cannot observe them “at idle”. only at a forced 1000rpm, and this is achieved by opening the iac.
im unclear on exactly what you are trying to do, but, the best way to have a great idling 85 is to first rule out vac leaks, i use cigar smoke blown innthe brake booster vac hose, with tape over the throttle body.
then follow the minimun idle set procedure, and use 550 minimum with iac closed. and finally, if you have an auto/700r4, find the factory hlh3200 prom chip. It will run perfectly after this. assuming no vac leaks or other issues.
“un-f-ing” TPI’s from well intentioned owners attempting to adjust idles is common. get the hlh3200. u will thank me later 👍
the 85, and 84, can only be scanned in field test mode.
among other things, this mode forces the car to run at 1000rpm. the long and short of it, is that you cannot set the idle rpm / iac counts / tps positions while scanning due to this. example, you may want to tune your iac to be 50 at idle. U cant, on 85 and 84, because you cannot observe them “at idle”. only at a forced 1000rpm, and this is achieved by opening the iac.
im unclear on exactly what you are trying to do, but, the best way to have a great idling 85 is to first rule out vac leaks, i use cigar smoke blown innthe brake booster vac hose, with tape over the throttle body.
then follow the minimun idle set procedure, and use 550 minimum with iac closed. and finally, if you have an auto/700r4, find the factory hlh3200 prom chip. It will run perfectly after this. assuming no vac leaks or other issues.
“un-f-ing” TPI’s from well intentioned owners attempting to adjust idles is common. get the hlh3200. u will thank me later 👍