More PCM tune questions

[dhanger]

I know PCM tuning is discussed ad nauseum all over the place but it's a bit difficult to pull together everything I need to know specifically for my case. I just had the tranny rebuilt and I'd like to have the tuning done mostly for the benefit of the tranny plus the performance improvement.

My TB is the only ride for me and my wife so I can't go without it long enough to send it in and have it done. I contacted Jeremy at Lime Swap about a loaner or junkyard PCM and here's what he told me:

8) I no longer offer the loaner service. You can send me a junkyard PCM, but the make, model, year, and gear ratio all have to match

So I plan to grab one from the pick and pull but not sure of myself. As I understand it the gear ratio is listed as an RPO code in the glove box? I found an RPO spreadsheet here so I'm assuming that's my best option to clear that up. Based on the attached photo and cross referencing the spreadsheet I see GT4/3.73 ratio, so I'm pretty sure I have that covered. Also what's the easiest way to check the model year, I don't see model years in the RPO list. The VIN has it I'm sure but don't know how to decode it.

I'm planning to ask for the air injection codes deleted, I've owned the vehicle for 20 years and never had a related DTC show up for that but I'd like to be proactive about it and knock it out before it happens. Any other favorites I should ask for on my 2004 TB LS? I'm not planning any mods so not looking for anything unusual. I did ask Jeremy about Passlock, his reply:

1) I would leave passlock stock on a Trailblazer. This option is mostly for folks with a Colorado, as those systems fail a lot.

Any comments on that?

Thanks,
Dan

 

[dhanger]

Okay, I did find the model year in the VIN code so that question is answered:

VIN-to-Year Chart | ALLDATA

The VIN (Vehicle Identification Number) is a serial number used to identify an individual vehicle. The VIN for each vehicle is unique.

www.alldata.com

 

[Mooseman]

Also what's the easiest way to check the model year, I don't see model years in the RPO list. The VIN has it I'm sure but don't know how to decode it.

That would be in the VIN itself, 10th digit. In the pic is a 2004.
(you answered that one yourself while I was typing )

I'm planning to ask for the air injection codes deleted, I've owned the vehicle for 20 years and never had a related DTC show up for that but I'd like to be proactive about it and knock it out before it happens. Any other favorites I should ask for on my 2004 TB LS?

Definitely kill the SAIS codes. Next would be the fan codes so you can use a thermal fan clutch from a 2008 instead of the failure prone electro-viscous fan clutch when yours does fail. I'd have the shift firmness increased to a medium just to reduce heat and wear from comfy slipping clutches. Then, have the TCC lock up 100% instead of slipping to lockup to reduce wear of the TCC and the valve in the valve body. It will feel like a 5th gear. Have torque management removed so the engine feels snappier. Never regretted that one . If you want, you can also have the 100 mph speed limiter removed.

Unless you live in an area prone to auto theft, I'd still have the Passlock taken out. It can, and has failed on our platform too. You still have to do the 30 minute security relearn with the "new" PCM.

Be sure to try the new PCM in your truck before sending it just to be sure it works after the security relearn (you won't have to redo it again when it comes back). You will need a CASE relearn requiring a high-end bi-directional scan tool or a Tech 2 or you'll have to take it to a shop or dealer that can do it. You will be able to drive it.

Be sure to keep your old PCM as a spare. It will work without anything to be done to it.

 

[dhanger]

Be sure to try the new PCM in your truck before sending it just to be sure it works after the security relearn (you won't have to redo it again when it comes back). You will need a CASE relearn requiring a high-end bi-directional scan tool or a Tech 2 or you'll have to take it to a shop or dealer that can do it. You will be able to drive it.

Thanks, that's the kind of info I was looking for. Regarding the CASE relearn, I understand that if the crankshaft position sensor is replaced the relearn procedure is required also. I have never replaced the sensor; since I have to do the relearn anyway is there any reason I should make a pre-emptive strike and replace the sensor at the same time?

 

[Mooseman]

Because the crank angle is specific to each engine, the used PCM will have the learned angle from the junker and may not be the same as yours. You could replace the crank sensor however I haven't heard of many of these failing. You could try it for a while and see if it trips a code for it. It won't prevent the engine from running. It's only to report when the timing chain is over-stretched.

 

[dhanger]

I see, so I infer that the whole reason the PCM has to do the relearn is *because* of the inherently wrong angle. I think I'll just skip replacing the sensor and only do it when necessary.

Thanks for the help on this issue.

 

[dhanger]

I've had the tune done and installed for a few weeks and not real sure about some aspects of it. For one thing I'm a little confused about the fan delete (having the EV coupling on mine), does deleting it remove any kind of pcm control over it? I'm asking because I noticed that the common roaring at cold startup disappeared after the tune which left me wondering if it's engaging at all. It's now 110+ degrees here in Arizona and I decided to check--at idle and normal operating temp I can stop the fan by hand which doesn't seem right to me. I'm not having any overheating problems so that's good.

I have Torque Pro and Car Scanner Pro but I don't see a fan speed PID, maybe the fan speed is not monitored by a sensor? Was thinking that might help to determine what's going on.

 

[mrrsm]

This... From Nomic's *GPT4ALL* using the Llama Ver. 3.2 "Instruct" 128KB LLM (Large Language Model) Prompt Window:

First.. Your initial Post:

Prompt:

2004 Chevrolet Trailblazer 4.2L Engine AFTER the PCM has had the "Fan Delete" re-programmed and after I installed Electric Fans insted: I've had the tune done and installed for a few weeks and not real sure about some aspects of it. For one thing I'm a little confused about the fan delete (having the EV coupling on mine), does deleting it remove any kind of pcm control over it? I'm asking because I noticed that the common roaring at cold startup disappeared after the tune which left me wondering if it's engaging at all. It's now 110+ degrees here in Arizona and I decided to check--at idle and normal operating temp I can stop the fan by hand which doesn't seem right to me. I'm not having any overheating problems so that's good.

I have Torque Pro and Car Scanner Pro but I don't see a fan speed PID, maybe the fan speed is not monitored by a sensor? Was thinking that might help to determine what's going on.


Nomic's *GPT4ALL* Reply (Off-Line... No Internet Connection):

Response:

An interesting question about the fan delete and PCM control on your 2004 Chevrolet Trailblazer with a 4.2L engine!

The "Fan Delete" re-programming you mentioned is likely referring to a modification that removes or disables the factory-fitted electric cooling fan, which was controlled by the Powertrain Control Module (PCM). The EV coupling you're talking about might be related to this.

Here's what I found:

1. **Fan delete and PCM control**: When the "fan delete" re-programming is done on your vehicle, it typically involves modifying the engine computer (PCM) software to no longer activate or control the electric fan at specific conditions (e.g., high temperatures). This modification can be useful for vehicles that don't need the additional cooling assistance under normal operating conditions. However, this doesn't necessarily mean the PCM has lost all control over the fan.

2. **EV coupling**: The EV coupling is likely a component related to the electric fan's operation. It might be used to connect or disconnect the fan from its power source (e.g., battery) when not needed. If you've had the "fan delete" re-programmed, it's possible that this modification has disabled the PCM's control over the EV coupling as well.

3. **Fan speed PID**: You're correct in assuming that there might be no fan speed PID available on your Torque Pro or Car Scanner Pro tools. This is because modern engine computers often don't provide direct access to fan speed data, especially if it's not a critical parameter for monitoring.

Given the information you've shared:

* The roaring noise at cold startup has disappeared after the tune.
* You can stop the fan by hand when idling or operating normally (at 110+ degrees).
* No overheating issues have been reported.

It seems likely that your PCM is no longer controlling the electric fan, and its operation might be limited to only engaging under extreme conditions. However, without direct access to a fan speed PID on your scan tools, it's difficult to confirm this with certainty.

To better understand what's happening:

1. **Consult the tuner**: Reach out to the person or company that performed the "fan delete" re-programming and ask them about their specific implementation details.

2. **Check for additional parameters**: Look through Torque Pro or Car Scanner Pro documentation (or contact support) to see if there are any other PIDs related to fan operation, such as a temperature threshold parameter or an activation/deactivation flag.

Keep in mind that the absence of overheating issues is good news! If you're not experiencing problems with your engine's cooling system, it might be best to monitor its performance and wait for further clarification on this matter.

 

[dhanger]

Hmmm, well I'm not really sure what all that is telling me. There were a couple of references to an electric fan but I do not have that, I still have the original viscous coupling fan from before the tuning fan delete.

A little more info about why I'm asking. A few months ago I did a complete A/C kit replacement and have had a few issues with it since (I will probably start a new thread to discuss that). Last week I took a long road trip through the Southwest and the a/c worked well with ambient temps. in the high 90s/low 100s. After returning home I took a drive in 115 degree temp and started having lots of trouble getting cold air so I started wondering if the fan delete was preventing the viscous fan from cooling the condenser adequately.

 

[mrrsm]

Right now... ALL of the Large Language Models rely upon the extent of their "Machine Learning Corpus" ...which is to say that in some cases, their "Advice" must be taken "With a Grain of Salt".

At their present level of development, the AI LLMs become helpful whenever they can steer our thoughts in directions which have NOT been conventionally arrived at and accepted as Gospel... from Human Factual and Empirical Knowledge and become suggestive of alternate approaches to problems.

So far... the Llama Ver. 3.2 "Instruct" LLM ...with its broad 128K Prompt Entry Window... runs about being 85% accurate whenever most problems are put to it.

I have another more sophisticated "Reasoning" AI LLM aptly called "Reasoner" from Nomic for dedicated use with the *GPT4ALL* Chat-Bot that I'll run your First Post through... just to see if the response is any different. I do think that the LLM's last advice above was very similar to what a Human Being might *Think* in that:

"If It WORKS...Don't FIX It..."

PS... Regarding driving around in 115 Degrees Fahrenheit Temperatures... approaching those of "Death Valley"... With the amount of difference between the HVAC Super-Heat vs. Sub-Cooling required in order to vector (reject) the Cabin Heat collected by the Evaporator Coils under the Dash and then "easily" expel it out into the ambient air via the action of the New Fan(s) pulling Outside Air across the A/C Condenser Coils ...is really asking too much of ANY A/C operating under such terrible Thermal Conditions.

 

[Mooseman]

m a little confused about the fan delete (having the EV coupling on mine), does deleting it remove any kind of pcm control over it?

No. It just turns off the codes if it ever fails and you replace it with a thermal clutch.

After returning home I took a drive in 115 degree temp and started having lots of trouble getting cold air so I started wondering if the fan delete was preventing the viscous fan from cooling the condenser adequately.

Maybe you clutch has failed. Test your clutch as per this thread:
How to test the electro-viscous fan clutch

 

[dhanger]

Thanks MM, I'll do some testing. If the clutch had failed with the original PCM (before fan delete) would that send a code? It's only been a few weeks since swapping in the tuned PCM and I hadn't had any codes at all prior to swapping, and it would be a little strange that the clutch would go bad in that time frame.

 

[dhanger]

Actually I just realized I had already performed that diagnostic test as I had reported in post #7. With the engine fully warmed up and a/c on full I was able to stop the fan, so apparently that means the clutch is definitely shot and likely was for some time before the tuning, although I never did get CEL.

So now that I have the fan delete and don't need to get the same EV clutch what are the recommendations for a replacement fan, hopefully drop in?

 

[dhanger]

Okay, did a little searching and found that this thermal clutch is what Mooseman recommended after a fan delete:

https://www.amazon.com/dp/B00276J4ZW/?tag=gmtnation-20

Is this still a good unit for this application? I see that others have gone with electric fan setups but that seems like much more work and expense than this option. Only advantage I saw with electric is that it frees up a small amount of HP from the engine, but I'm all for simpler and cheaper in this case.

 

[Mooseman]

That's the one I'm using and it works fine. A/C is also ice cold with it.

Electric fans are a fallacy on this platform. I drank that Koolaid and it was terrible. Poor cooling and A/C performance. The big problem is that our radiators are marginal and the engineers overcompensated with a mechanical fan. If they would have put a decent rad, they would have put in e-fans themselves for fuel savings. Save yourself the aggravation and put in a new clutch.

 

[dhanger]

This morning I installed the new Hayden thermal fan clutch. It immediately solved my a/c problem. I mentioned doing a complete overhaul of the a/c system earlier this year but I couldn't solve the problem of the compressor cycling on and off and pressures fluctuating. In fact I tore it all apart a couple of times to make sure I didn't inadvertently create a restriction somewhere. It never occurred to me that the fan clutch was defective; this was prior to deleting the fan from the PCM and I wasn't getting any DTC's from the fan clutch to clue me in. Very happy with the results, and all my efforts at renewing the A/C finally paid off. Getting 43 degrees at the vents.

 

[dhanger]

Hey everybody, I'm reviving my old thread because there is info here that is pertinent to my question and thought it would be helpful to have it all together.

Refresh: pulled a junkyard PCM to have Lime Swap tune it for tranny performance and some code deletes (EV fan replaced by thermal clutch, AIR delete). Kept the OEM PCM on the shelf for emergencies.

Recently I became aware of a possible emissions issue, namely that the PCM is what reports the VIN and obviously a junkyard PCM is not going to match my dashboard VIN. The question that came to mind is what problems will that cause at smog testing time--I've been doing smog checks on the car for the whole 20 years I've owned it, in the same region requiring testing. Each time the test is done I always noted that at the end of the test the tech would compare the VIN on the printout with the VIN on the dash. Could that be a problem? It took me a while to track it down but I finally talked to someone in the dept. who told me yes, that would be a problem. He also mentioned that any tuning done could cause issues--I asked him specifically about the AIR system for example and his reply was vaguely 'could be a problem'.

I'm sure this has been dealt with by other people in emission testing areas but since my question is specifically for Arizona maybe nobody knows (except possibly @azswiss who lives in the same county as me). I can correct the VIN issue by sending my OEM module to LimeSwap and have my tuning duplicated but that doesn't address the other deletions, etc.

Am I worrying about nothing?

 

[azswiss]

Can't speak to the code deletions but the VIN mismatch will definitely be an issue.

 

[Mooseman]

Back when we used to have e-testing, I had a mismatched PCM on my 02 EXT. During the test, the guy took the camera and showed to the "official" at the other end the VIN on the dash and the door jamb. That was probably to confirm that the PCM was a replacement. Mine was tuned for performance and fan deletion.

Probably depends on how strict they are. In CA, the mismatch would probably never fly and they would also notice the tune as the checksum would be off. If AZ is not one of those states that follows CA rules, you should be fine. As long as you don't have any of the main codes turned off, like evap and O2 sensors, and that the I/M readiness is good, you should be fine.

 

[dhanger]

Okay, well that's enough info to formulate a plan. I will definitely send Jeremy my OEM module for duplication of tuning to get past the VIN mismatch (live and learn....). I'm not due for registration until May '27--AZ let's you do your smog check up to 90 days in advance so that gives me some breathing room if it doesn't pass to come up with a plan. Thanks.

 

[Aroc]

I have Torque Pro and Car Scanner Pro but I don't see a fan speed PID, maybe the fan speed is not monitored by a sensor? Was thinking that might help to determine what's going on.

To monitor Fan Speed on Car Scanner Pro:

Header: 6C10F1 (Auto)
PID: 22162B01
Formula: A*16

It always takes a good 3-5mins after cold startup to stop roaring in any ambient temperature. Must be the open loop fuel control period.

 

[Mooseman]

It always takes a good 3-5mins after cold startup to stop roaring in any ambient temperature. Must be the open loop fuel control period.

The roaring is caused by the silicone fluid going out of the reservoir and into the clutch part. Apparently it's dependent on which position the fan clutch stops at. Even the thermal clutches do this (mine does occasionally).

M

Thread 'Reason for fan at startup?'

May 22, 2014

'08 9-7x 4.2i. Sometimes when I start the truck the fan is on, for what seems to be for no reason at all. Sometimes it's hot out, sometimes it cold out. It will be on from startup and usually only stays on about one minute. Any ideas?

• MindBlowin03
• Replies: 21
• Forum: Technical Discussion

 

[dhanger]

After the tuning I installed a Hayden 2851 thermal clutch. It sounds like 2 jet engines at startup and doesn't quiet down until full operating temp. Way louder than the original electronic clutch even.

 

[Mooseman]

Check to see if it stops at the same position all the time. If your fan is slightly unbalanced, it could be stopping in the same position all the time. Try rotating the fan 180deg on the clutch (the 4 bolts).