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Ok. Now this may sound like a really weird question....are you absolutely positive that the ABS isn't activating when you're slowing down? The ABS pump activates briefly during its self check shortly after startup (or when you first start moving...can't recall which). In every 90s/2000s GM i've driven, including a 2000 Regal, the ABS pump initially kicking in would often cause a bit of a power dip (headlights dimming slightly, blower speed audibly slowing slightly etc..). Something that I have also had issues with in some of those vehicles has been unwanted ABS activation from weak/failing wheel speed sensors and/or failing tone rings. You may need to really listen and feel for an unwanted ABS activation, as it can range from being a very quick and random engagement of the pump that you don't really feel.... to full on constant ABS activation with the pushback of the pedal and the sensation of a loss of braking power.

The latter would be a better description. It’s like a large draw and they will dim then go back to normal. Sometimes it does it once’s, sometimes a few times in a row

You'll have to define the pulsing. Is it like a continuous flicker, or is it more along the lines of a large draw where the lights briefly dim once and then come back up?

And it worked as designed yesterday...

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Hello everyone! i have recently acquired a 2002 Buick Regal. This car was a one owner car and I picked it up in October with 74k miles on it. It has been very well taken care of. I bought this car because of the reliability factor, however I have fallen in love with how it drives! The only issue that I am having is intermittent headlight pulsing. It only happens when the car is decelerating and slowing down under 30mph or so. So far I have replaced the battery, had the alternator tested(tested good ), went and bought another alternator and installed just in case of possible voltage regulator. Also found and cleaned thee grounds under the fuse box, next to the drivers headlight, and the engine ground by the exhaust. I have also ran a big 3 wire upgrade (did this for future sound system) as well as an extra power wire from fuse box to alternator(saw some videos where people said this extra line helped)This seemed to make my headlights a bit brighter, but not affect on the pulsing. All that being said i am still getting the same result. The interior lights will dim for a moment when the car first starts and the the headlights on deceleration. From what I have found there is no headlight relay, only fuses. I have one friend who has suggested new bulbs, however I am not convinced this would fix anything as they are older but still light up well. Any suggestions on where to look next would be greatly appreciated!

Right. That's confusing; seems like it is routed incorrectly. Worked perfectly fine yesterday. Even more confusing.

Yep....that's what I was going to do until I ran into a couple of hurdles.....no supplier on this side of the border had the aluminum crimps available, no supplier on ebay in the states at that time who had them would ship across the border, no shop in the nearby area had the equipment to fabricate custom a.c lines. Go figure

Since this has turned out to be more complicated than I initially thought, I think I'm going to just go with custom made AC lines. I can use both stock 92 Cutlass lines from the evaporator, the drier, and condenser. Then all I need is to cut and splice the Impala compressor-end hoses to the Cutlass condenser+drier ends. Two hoses, 4 crimps, no problem!

I had a fun chat with ChatGPT and learned some possible solutions. One is to just use an aftermarket pressure switch, wired inbetween the Cutlass HVAC module AC Rquest and clutch relay. Another option is an 02-03 GTP PCM (also 00-02 Regal GS and 02-03 Bonne SSEi are potentials). It's an L67 with an 4T65-EHD, plus is has a discrete AC Signal request input instead of a Class2 signal from a BCM. I'll just have to repin a few wires at the PCM connectors. The GTP is probably a great choice because it has full support in HP Tuners, which I already own. The 04 Impala PCM is supported in HPTuners also but I don't think it supports all features.

I'm definitely not looking to go with a manual switch. Let me see if I understand how the system works in the 04 Impala... The HVAC Control Module has an AC Request Switch, when driver wants the AC on, it outputs a Class 2 Serial signal to the BCM. The BCM doesn't appear to have any other direct inputs related to the system, so it might just pass that along to the PCM. The manual does specifically state that the AC Request signal comes from the BCM, not from the HVAC module. In any case, the PCM needs a Class 2 Serial input containing the AC Request On signal. Then the PCM decides along with the other inputs if it should engage the clutch. If it doesn't get this signal, the PCM will never trigger the clutch relay to engage. So if that's all correct, I think I have three options. 1) Find out if there's a PCM that will run the L67 but doesn't use a Class II signal for the AC Request Signal. 2) Simulate a Class II Serial signal with an Arduino including an AC Request On message. Other forums have decoded the signals, further research is needed to determine if this is feasible. 3) Bypass the PCM entirely, again with an Arduino. Take the AC Request signal from the Cutlass HVAC module (which I think is actually just 12v switched?), the AC Pressure Switch, optionally Power Steering pressure switch, throttle position, and coolant temp sensors, all into an Arduino programmed to power the clutch relay under the right conditions. None of these options sound fun! What is different about my swap that makes this neccessary? Tons of people have put 3800's in W-bodies and I've not seen anyone talking about AC issues.

I doubt that any of those PCMs would do what you’re wanting them too. I don’t know about the Lumina, but even 97 2nd gen cars would have used class 2 data from the BCM to receive the AC request signal. The Lumina PCM being from an NA car would also pose a different set of challenges altogether though. GM was famous for changing things like the crank/cam correlation, crank sensor patterns, sensor types etc….on the same engine over the years, so an older PCM for a series 2 L67 may not even work with a newer one. Also take into account when those write ups were written. In the mid-latter 2000s, using a 2004 as a donor car wouldn’t have been common as they were still too new, which might be why the references are to older ones. Assuming this isn’t a daily driver, I’d almost consider going the manual compressor switch route. The power steering and WOT compressor cutouts aren’t overly critical, and the low and high pressure refrigerant switches should be easy enough to integrate into a manual AC compressor switch.

I would use an older PCM from a different 3800, which is what every swap guide I read suggested in the first place. I used the engine-matching PCM because it ended up being easier, but there must be reasons previous swappers used late 90's PCMs instead. I also have an 2000 GTP and 98 Lumina LTZ PCM. Both of them tested to start and run the engine, but both had different transmissions and the LTZ is N/A. Both would need programming, but one of them might have a compatible switched ground AC request signal. Surely I'm not the first person to have AC in their L67 swap!?

Taking a good look at the potential V5 contenders, it's apparent that you are going to be limited to a V5 from only the 3.8 engine family. Attempting to use a V5 *134a* from a '96 60 degree engine will not clock properly & the housing castings are different & not compatible with the 90 degree engines. This means you can't use an ODB1 V5 compressor at all. Since you're stuck with a 134a compressor you have to use the 134a hose manifold assembly which will not fasten to your existing receiver/dryer unless you go to the effort of cutting off the pipe ends & swapping them & tigging the old fittings to the new manifold. The same B.S I went thru.......... if one doesn't go the *custom* route you have to change both the receiver/dryer & the liquid & gas line into & out of the evaporator core.

Swap the PCM with what though? The cutlass PCM won’t run the L67. A 3rd gen PCM from a 3800 series 3 car won’t run a series 2 L67 either…and even then it would still rely on BCM input for the HVAC.

In the 04 Impala it's the Class 2 Serial line, shared with the BCM, PCM, HVAC, everything really! If I knew the protocol I could potentially simulate it using an Arduino, like I'm doing for the ALDL input on my UB3 cluster tachometer. Or I can still just swap the PCM. In either case it looks like the Cutlass HVAC module and whatever PCM I use need to be able to communicate.

Do you know what the AC request signal is though from the BCM? On the Cutlass, the request is in the form of a power or ground signal applied to a specific PCM pin. The PCM will then use a combination of other inputs to determine if and when to allow the compressor clutch to engage. Not having proper input from the powertrain side of things on the Cutlass PCM might not allow it to enable the AC compressor. On a 2004 Impala, that AC request signal from the BCM may very well be in the form of a communication between BCM and PCM rather than a simple power or ground switch. From an operational perspective, the V5 adjusts internally based on refrigerant pressures….so the option to bypass everything and run a separate toggle switch to enable the compressor might be required in the end anyways.

This is a Series II L67.

I'm not familiar with the series 3 L67, I've only dealt the series 2, is there any sort of block casting redesign that will prevent one from fastening the V5 compressor to where the cvc is mounted?

I'm looking at the 04 Impala FSM. The BCM *is* part of the system, but it's only a A/C Request Signal which connects to the HVAC Control module. Since I'm not using the Impala control module, I don't think that matters. I am using the Cutlass module. I also don't see any special circuitry for the CVC function. It's just a normal looking clutch either off or on, no other electronics for the compressor.

Because of the physical mounting, or because of the PCM? I can swap PCM if needed to use a different compressor, but If i'm limited to this 04-08 compressor mounting style, I will almost certainly need to make custom lines since they use a completely different line configuration.

One thing to be careful of there is that 2004 was a bit of a transitional year. A 2004 Lacrosse is a 3rd gen W and came with the 3800 series 3, while the 2004 Monte/Impala was still a 2nd gen and came with the 3800 series 2. Compatibility wise, you’re very much going to be stuck running a compressor compatible with a 2004 Monte SS if you want any hope of things functioning properly. The other potential gotcha is that 2nd gens also ran a BCM. There is a possibility that the PCM requires input from the BCM in order for the AC compressor to run correctly in the first place.

Yes, there is currently the original 04 Impala compressor installed, but I will need to replace it. It's been disconnected from the lines for years since the initial swap and the inlet and outlet have not been plugged, who knows what kind of gunk has gotten in it. So I am replacing *everything* except (if I can avoid it) the evaporator.

I see, but the powertrain you have in the car is from the same 04 Impala?......so the a/c compressor mounted to that block would be the cvc unit....and that's what currently still mounted to the engine?.....if you've removed the compressor what are you using for a pulley to take the place of the compressor?