I was recently informed about the V5 A/C system that was used on 1986, 87, and 88 Fiero 2.5L IL4 TBI models. I don't know much about the IL4 models so I read up on the V5 system.
I am told that the the V5 system was introduced in 1986 and that you must use a 1986 ECM with that system (for that model year). But 1985 and 1986 used the exact same ECM (1226864). I studied the 1985 DA6 system diagrams, the 1986 V5 system diagrams, and read the 1986 Service Manual section on the V5 system. The V5 has a clever variable compressor feature that makes it more efficient without cycling.
My conclusion is that the 1226864 ECM (used for 1985 and 1986 IL4 ECMs) will work with either system. Each have different compressors, control/pressure/cycle switches, and relays, but they are all external to the ECM, so it appears that in the case of the 1985 and 1986 model years, either ECM will work with either the DA6 or V5 system. It makes sense that people are told to use a 1986 1226864 ECM with the V5 because that is the year the V5 system was introduced, but since the 1985 ECM is the same model, it should work just as well with the V5 system. I don't think the PROMS have any specific air conditioning parameters that make any difference between the two systems because each control their compressor cycling/variations externally from the ECM. The ECM is basically enabling/disabling the system connected to it.
I was recently informed about the V5 A/C system that was used on 1986, 87, and 88 Fiero 2.5L IL4 TBI models. I don't know much about the IL4 models so I read up on the V5 system.
I am told that the the V5 system was introduced in 1986 and that you must use a 1986 ECM with that system (for that model year). But 1985 and 1986 used the exact same ECM (1226864). I studied the 1985 DA6 system diagrams, the 1986 V5 system diagrams, and read the 1986 Service Manual section on the V5 system. The V5 has a clever variable compressor feature that makes it more efficient without cycling.
My conclusion is that the 1226864 ECM (used for 1985 and 1986 IL4 ECMs) will work with either system. Each have different compressors, control/pressure/cycle switches, and relays, but they are all external to the ECM, so it appears that in the case of the 1985 and 1986 model years, either ECM will work with either the DA6 or V5 system. It makes sense that people are told to use a 1986 1226864 ECM with the V5 because that is the year the V5 system was introduced, but since the 1985 ECM is the same model, it should work just as well with the V5 system. I don't think the PROMS have any specific air conditioning parameters that make any difference between the two systems because each control their compressor cycling/variations externally from the ECM. The ECM is basically enabling/disabling the system connected to it.
Can anyone verify this?
if you tell me how to get data off of the prom i have a 84 auto, 85 manual with ac for prom chips and a 87 2.8 with ac so we can see if anything is the same
[This message has been edited by cartercarbaficionado (edited 06-04-2025).]
RWDPLZ responded with a TON of information further down. He talks about the ECM, which still has me a little confused as to what the ECM does here, but this particular paragraph is important:
"Although shown in the same location in the diagram, the V5 low and high pressure switches don't perform the same function as the DA6/HR6 cycling switch: Rather they use the same input pin on the ECM. The V5 system also uses the fan control pin on the ECM to CUT the fan if pressures are too low (if pressure is too low, you'd actually want to warm up the condenser to increase pressure).
In order to use the V5 compressor in the DA6/HR6 car, you'd want to cut the signal wire to the cycling switch, and run new wires from that ECM pin to the switches on the compressor, wired in the same way. Note the locations of the C100 and C203 main connectors in the diagram in relation to the switches.
Again, I'd just put an HR6 compressor in the car and be done with it, far simpler and cheaper solution."
It looks like this information might be confirming what you've found in the ECM code. Sorry if I led you down a rabbit-hole... but I appreciate all the work you put into this. I think everyone should upgrade to the V5!
[This message has been edited by 82-T/A [At Work] (edited 06-05-2025).]
My research yields just what FieroGuru said, the ECM has little to do with air conditioning other than to temporarily disable it at high RPMs, alter the Idle when the A/C is loading the engine, shut it down at high CTS temperatures (in case the Fan Switch fails), enable the Radiator Fan if the A/C is turned on (Il4s), temporarily disable it if the Power Steering is under high load, and monitor if the Compressor is on or off at the moment.
I will check out the link.
[This message has been edited by Romsk (edited 06-05-2025).]
It's entirely possible the code to run a V5 compressor may be present in the 85 ECM's PROM chip - They may have planned to introduce the V5 compressor earlier than they did, and it was bumped to the following model year. It also may be present if it was used on other GM cars that had a V5 compressor, I doubt the computers and code were Fiero specific in an organization as large as General Motors at the time. If you actually found power steering code in it, that would also support the theory, as Fieros didn't have it and IIRC power steering prototypes weren't in development until 1986? and in cars until 1988.
I have never used TunerPro, so I have never seen what is in Fiero PROMs.
I agree, there is probably nothing specific for A/C from year to year in the ECM code or PROMs. In the Repair Manual, it was mentioned that if the Power Steering is under high load, it will cut off the compressor. But even if virtually every Fiero didn't have Power Steeting, the signal is pulled inactive high internally in the ECM and thus defaults to inactive.
I assumed that on IL4 ECMs, the fans are turned on and the compressor is turned off if the CTS reads too hot (a backup for the Fan Switch on the Engine). The V6 ECMs don't control the Fan for some reason.
Adjusting Idle when the Compressor is on probably has just a flag in the PROM: 'Adjust Idle with A/C Compressor is On'. Since a Fiero with no A/C will never activate the A/C_On signal, I am sure all PROMs would have that flag enabled if A/C is installed or not. There is no feedback from the Compressor to the ECM, so it has no way of knowing how much load the Compressor is putting on the Engine, let alone what type of A/C System is used.
I have never used TunerPro, so I have never seen what is in Fiero PROMs.
I agree, there is probably nothing specific for A/C from year to year in the ECM code or PROMs. In the Repair Manual, it was mentioned that if the Power Steering is under high load, it will cut off the compressor. But even if virtually every Fiero didn't have Power Steeting, the signal is pulled inactive high internally in the ECM and thus defaults to inactive.
I assumed that on IL4 ECMs, the fans are turned on and the compressor is turned off if the CTS reads too hot (a backup for the Fan Switch on the Engine). The V6 ECMs don't control the Fan for some reason.
Adjusting Idle when the Compressor is on probably has just a flag in the PROM: 'Adjust Idle with A/C Compressor is On'. Since a Fiero with no A/C will never activate the A/C_On signal, I am sure all PROMs would have that flag enabled if A/C is installed or not. There is no feedback from the Compressor to the ECM, so it has no way of knowing how much load the Compressor is putting on the Engine, let alone what type of A/C System is used.
Thanks for confirming my suspicions. Paul
im probably wrong but isn't the biggest fit issue if it bolts on and has the right pulley?
Mechanically, yes, that is a big difference. I was focused more on the ECM because it is widely thought that a 1986 (and later) IL4 ECM must be used with the V5 A/C System as that was the year that system was introduced for those Fieros. What puzzled me is: the 1895 IL4 Fieros used the same ECM, so I was questioning if a 1985 ECM could be used as well. After discussing this with several folks, and my studying the circuits of both the 1985 ECM with the DA6 A/C system and a 1986 ECM with a V5 A/C system, the general consensus is either A/C system can be used with either ECM year (they being the same ECM model number). This is because both systems are different externally to the ECM, but from the ECM's functions, it doesn't know (or work differently) for either system. I could be wrong, but the evidence seems to point this way.
The reason I was exploring this is: I am expanding the Fiero ALDL Monitor GUI and Adapter to support IL4 Fieros (as it currently only supports V6 Fieros). So, when I learn new features for Fieros, I tend to explore each nuance for my own edification.
82-T/A was kind to lend me his 1986 IL4 ECM for that effort. The subject came up, so I dug in a little deeper and then created this thread to discuss it further.
I think the V5 Compressor with it High/Low Pressure Switches is the only difference between the two systems (each use the same Evaporator, Expansion Valve, and Condenser). The V5 has constantly variable compression, where the DA6 has cycling compression. So I would imaging different belts and brackets might be required. 82-T/A might shed some more light on the mechanical differences.
Paul
[This message has been edited by Romsk (edited 06-08-2025).]
Mechanically, yes, that is a big difference. I was focused more on the ECM because it is widely thought that a 1986 (and later) IL4 ECM must be used with the V5 A/C System as that was the year that system was introduced for those Fieros. What puzzled me is: the 1895 IL4 Fieros used the same ECM, so I was questioning if a 1985 ECM could be used as well. After discussing this with several folks, and my studying the circuits of both the 1985 ECM with the DA6 A/C system and a 1986 ECM with a V5 A/C system, the general consensus is either A/C system can be used with either ECM year (they being the same ECM model number). This is because both systems are different externally to the ECM, but from the ECM's functions, it doesn't know (or work differently) for either system. I could be wrong, but the evidence seems to point this way.
The reason I was exploring this is: I am expanding the Fiero ALDL Monitor GUI and Adapter to support IL4 Fieros (as it currently only supports V6 Fieros). So, when I learn new features for Fieros, I tend to explore each nuance for my own edification.
82-T/A was kind to lend me his 1986 IL4 ECM for that effort. The subject came up, so I dug in a little deeper and then created this thread to discuss it further.
I think the V5 Compressor with it High/Low Pressure Switches is the only difference between the two systems (each use the same Evaporator, Expansion Valve, and Condenser). The V5 has constantly variable compression, where the DA6 has cycling compression. So I would imaging different belts and brackets might be required. 82-T/A might shed some more light on the mechanical differences.
Paul
i could loan you my 1987 ecm but id want it back in case my current one quits.
I only borrow the ECMs. I plug them into my bench fixture to power them up, control inputs and outputs, and figure out how the ALDL works for it.
Currently, I borrow them for about two months before I send them back to the owner. I put a vivid yellow sticker on each one as to the owner and return address. The first guy to loan me his 1985 V6 ECM didn't even charge me for shipping. So I will be giving him my "Paperclip" Adapter and a Rear Trunk LED Lamp with Switch as "Thank You Gifts". I am waiting for the lamp lenses to come in. Then I will be shipping the gifts back to him along with his ECM. All by USPS insured delivery.
82-T/A lent me his 1986 IL4 ECM last week (and didn't charge me shipping either). I am in the process of making Edge Connectors for it because I can't use Pogo Pins on those connectors. This is delaying my analysis, but he will be getting Thank You Gifts as well once I am done with it.
Contact me at: romsk22@gmail.com
We can make arrangements by e-mail.
ECM 1226869 is for 1985 V6 Fieros 160 Baud (Covered) ECM 1227170 is for 1986-1988 V6 Fieros 160 Baud (Covered) ECM 1226156 is for 1984 IL4 Fieros 160 Baud (Need to Borrow) ECM 1226864 is for 1985-1986 IL4 Fieros 160 Baud (Covered) ECM 1227748 is for 1987-1988 IL4 Fieros 8192 Baud (Need to Borrow)
Because the 1987 IL4 ECM (1227748) uses 8192 Baud, I may need that for a couple of months more. That protocol will require additional research and a lot of code changes for my Adapter and GUI to support it.
Thanks, Paul
[This message has been edited by Romsk (edited 06-08-2025).]
im probably wrong but isn't the biggest fit issue [DA6 vs V5 compressor] if it bolts on and has the right pulley?
The pulley isn't really the problem. The DA6 and the V5 are both available in either V-belt or Serpentine belt configurations.
Side story... the 87-88 Fiero was really a leap compared to all the other Fieros at the time. Even though it was all based on the Iron Duke, it incorporated all the technology that the V6 either didn't come with or had the older version of. It was sort of a "must do" kind of thing because the 84-86 engines were so maligned in some ways. The automatic versions were exceptionally underpowered, and with the A/C on, the car almost couldn't get out of it's own way. A 5-Speed ~85 Fiero 4-cyl is actually quite quick, but again... with A/C, the car would lose a lot of power. In 1987, they incorporated the serpentine system with an ACTUAL belt tensioner. The Fiero's V6 engine did come with a much older version of the belt system, which was tensioned by the alternator. But the serpentine system on the Fiero was not really a serpentine system, so much as it was a serpentine belt routed like a V-belt... which is why it squeaked and sucked so bad. It also was only 5-grooves, compared to the much more modern standard of serpentine belt system on the 87-88 4cyl Fieros which used 6-grooves. Of course, rounding out that tangent, the 87-88 Fieros also came with DIS ignition, a more advance ECM, and a host of other things.
On the V6 Fiero, you can use a 1986 4cyl Fiero V5 compressor, which comes with a V-belt pulley on it. You can literally then just replace the big DA6 compressor with the V5 compressor, and it will fit in the brackets and work fine. The problem is that the V5 compressor is much smaller, about 30% less length than the DA6, and it no longer is supported by the rear brackets. This is not necessarily a problem, mostly because the original DA6 compressor could weigh in close to 20 pounds for some models, with the lighest ones coming in at 14 pounds. The heaviest V5 compressor I saw was just under 8 pounds... so there's a huge weight difference (respectively). You can install the V5 compressor without the rear bracket, and use only the front bracket, the only potential is that it could over time ruin the bearing on the compressor since there's the potential for the compressor to sit at a slight (unperceived) angle, since it's no longer suported in the back. You could probably easily make an L-bracket, or even get a bracket from a 1986 Iron Duke motor (and drill a new bolt hole).
The BIGGEST problem though (in my opinion) are the A/C lines. Because the A/C lines were different for every compressor for each year and each motor... you'll have to have a set of custom A/C lines made from the compressor to the hard lines. You could modify a set... but the V5 compressor is "clocked" differently... so you can't just re-use your old A/C lines as they MAY... MAY interfere with things like exhaust and whatever else. But you can try. Any A/C shop should be able to extend or bend the lines for you. But that was my biggest issue.
For my daughter's 85, we converted to a serpentine system, used an A/C compressor from a 1987-1988 4cyl Fiero, and then used the A/C lines from a 1986 4cyl Fiero. Everything just bolted up. On my daughter's Fiero, the compressor is fixed, like it is in a 1987-1988... and we use the new C130S alternator as the belt adjustment, in lieu of an actual belt tensioner (since the 84-86 blocks are different, and cannot use the 87-88 belt tensioner natively).
This video my daughter made talked about the V5 compressor as one of the upgrades. It starts at 3:15, and then there's a demonstration of the newer V5 compressor and how it works. Essentially, it's always running when turned on, doesn't cycle on or cycle off, and just adjusts based on how it's designed to limit the amount of load it puts on the motor's accessories when the engine is being driven.
I have a 1987 GT V6. I put a belt tensioner on it from a guy on-line. I hated the belt chirps and watching the Volts lamp come on if I drove through a puddle with a big splash. I used to have a link to his site, but when the site was removed, I removed his link. Too bad, it works great and it was very affordable.
I have a 1987 GT V6. I put a belt tensioner on it from a guy on-line. I hated the belt chirps and watching the Volts lamp come on if I drove through a puddle with a big splash. I used to have a link to his site, but when the site was removed, I removed his link. Too bad, it works great and it was very affordable.
I'd love to see a picture of it.
What I know a lot of people have done, is use an idler pulley from Rodney Dickman. It's a piece of welded 1/8" flat-stock steel with an idler pulley attached to it, which increases the surface area of the belt on the alternator and the crank pulley.
What I'd love to see though is a complete conversion to a 6-groove pulley system, that would also help as well.
EDIT: Another odd tidbit... but at some point, they changed the motor mounts for the Fiero and went with a hydraulic one. I think all 88s got it, but I THINK also the 87 4cyl might have gotten it too. It's a gel-filled motor mount that absorbs the vibrations of the motor. They're pretty expensive, like $200 compared to $35 for a basic replacement. The mounts are different slightly too...
[This message has been edited by 82-T/A [At Work] (edited 06-10-2025).]
My pullies are all 5 or 6? groove serpentine belts. I don't see anything special about my motor mounts.
The Tensioner is solid aluminum alloy - it's looks casted. It bolts to a spot on the block (forget what it was for). It has a spring inside where it bolts to the shaft with a flat idler pulley on it. There is a 1/2 square hole to put a 1/2 inch drive ratchet wrench on it. I did make some slides on it (see link).
It was from DodgeRunners Garage... his page is back.
