Bypass the PCM?

"zeontestpilot" (zeontestpilot) 08/19/2015 at 09:15 • Filed to: Jolly Roger

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So Jolly Roger has been sitting in my driveway because of a messed up PCM (Powertrain Control Module). My grandpa, the electrician that he is, said something that caught my interest, he said why not bypass it.

So oppo, bypassing the engine’s computer, how smart/dumb of a move is it? I know it runs the engine and what not, but is it even possible? If it is possible, what drawbacks would there be? Any input would be appreciated, as this is uncharted territory for me. My endgame is to have a 2nd working car, as cheaply done as possible.

BrianGriffin thinks “reliable” is just a state of mind > zeontestpilot 08/19/2015 at 09:25

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That’s....not a good idea. I don’t know about the PT specifically, but the PCM in most modern cars runs EVERYTHING. Lights, engine and timing, braking system, fuel pump pressure, etc.

What is specifically wrong with the PCM? Can't you source a cheap used one from the same model/year?

miadaman? yes please > zeontestpilot 08/19/2015 at 09:26

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Sounds like a cool thesis project. But considering PCM often consists of ECU (controls ignition timing, emission, a/f ratio at the very least) and TCU that basically shifts for you. I’m not so certain a few nights soldering would solve the problem cheaply. Getting a junked PCM still seems to be the cheapest fix.

It would be awfully fun to read about though.

RazoE > zeontestpilot 08/19/2015 at 09:31

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Is it a turbo? I heard you can run an SRT-4 PCM and get all that glorious power.

zeontestpilot > BrianGriffin thinks “reliable” is just a state of mind 08/19/2015 at 09:39

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It works when it wants too, mostly it doesn’t turn over 90% of the time. It’s the same issue for the last 2 times I took the car in; dashboard lights up but it doesn’t turn over. The stupid dealership told me the transmission range sensor was bad the first time, then the second time they said a wire got disconnected on the sensor ( no charge though this time). I have a gut feeling they either scammed me or neglected to continue looking for problems after they found the first one. This time I took it to a 3rd party mechanic, who figured it was the PCM, which they don’t fix.

I think it’s a bad ground or something, but I was told it would be $700 to fix (with labor). I told them to just tow it to my house.

zeontestpilot > RazoE 08/19/2015 at 09:41

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Nope, not a turbo. :/

zeontestpilot > miadaman? yes please 08/19/2015 at 09:42

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Would swapping the PCM’s really work?

pip bip - choose Corrour > zeontestpilot 08/19/2015 at 09:49

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rip it out , replace efi with a carby.

BrianGriffin thinks “reliable” is just a state of mind > zeontestpilot 08/19/2015 at 09:50

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If your issue is just with the wiring of the unit, yes*. If it’s grounding in the wiring harness, eh probably not. Junkyard PCM or somewhere that lets you test it would be your best bet.

*some states, when doing inspections, pull the VIN off the PCM. if you swap it, of course your VIN won't match. Ask your mechanic if you're in an inspection state.

miadaman? yes please > zeontestpilot 08/19/2015 at 09:51

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Did a quick lookup on google, seems Chrysler PCMs are encoded with the VIN and will shut the car down if it detects a mismatch. I would certainly look deeper into the possibility of reflashing a junkyard PCM at dealers with your car’s VIN/key info.

BigBlock440 > zeontestpilot 08/19/2015 at 09:54

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Carb it and throw on an MSD ignition.

zeontestpilot > BrianGriffin thinks “reliable” is just a state of mind 08/19/2015 at 10:00

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I’m in Michigan, I don’t think there are any inspections here, none that I’ve heard of at least. Especially with some of the cars I’ve seen on the road...

zeontestpilot > BrianGriffin thinks “reliable” is just a state of mind 08/19/2015 at 10:01

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I’m in Michigan, I don’t think there are any inspections here, none that I’ve heard of at least. Especially with some of the cars I’ve seen on the road...

zeontestpilot > miadaman? yes please 08/19/2015 at 10:02

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Reflashing means the dealership though....which I'm trying to avoid....grrr...

MontegoMan562 is a Capri RS Owner > zeontestpilot 08/19/2015 at 10:04

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Only inspection would be if you apply for a Salvage title, otherwise we gots no inspections.

It sounds like your best bet is to go to a pick-n-pull and look for a PCM. They gamble there is...does it need to be reflashed at the dealer? Does that PCM work? Gotta make sure it’s cheap enough to pick-n-pull to warrant the risk.

zeontestpilot > pip bip - choose Corrour 08/19/2015 at 10:05

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Excuse my un-knowledge, but what would that do?

SidewaysOnDirt still misses Bowie > zeontestpilot 08/19/2015 at 10:07

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I don’t get how you’d be able to do it unless you convert the car to run on a carb. It can be done, but is it really worth the effort? Why not try to go to a you-pick? I’m sure they’re full of PTs. Also, FWIW, they seem pretty cheap on ebay .

zeontestpilot > MontegoMan562 is a Capri RS Owner 08/19/2015 at 10:18

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That’s what I figured, MI is pretty loose when it comes to cars.

Someone else said the Chrysler PCM is Vin specific, which means it's a no go.

MontegoMan562 is a Capri RS Owner > zeontestpilot 08/19/2015 at 10:23

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Yeah that’s really the only way to go. Which sucks. I had to replace the PCM on our first Jeep (05 Jeep Liberty) had the local shop do the work and then they brought it to the dealer to get it flashed.

miadaman? yes please > zeontestpilot 08/19/2015 at 10:33

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To be fair, there seems to be some people on the interweb saying their pull-a-part replacement worked after $30 reflash at the dealer. In this case the difference being you’re paying ~$200 for the junk part and flash as opposed to $600 for a new unit.

But, this would hinge on whether the dealer in question would/can even do such a service for you. And seeing how this is potentially a common issue, there’s no saying the junk one won’t fail either. If it were me and I’m keen on keeping the car, probably would bite the bullet and pay OEM replacement. Otherwise salvage what you can and sell the rest if the price doesn’t make sense.

zeontestpilot > MontegoMan562 is a Capri RS Owner 08/19/2015 at 10:46

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Hoe much were you charged for it?

Brickman > zeontestpilot 08/19/2015 at 10:55

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Most likely not. My caravan has the same engine. The fuel injection relies on the camshaft position sensor, TPS, knock sensor, and possibly other sensors.

Junkyard run for a PT cruiser PCM would be the best. Should be all the same, but get one the same model year just to be sure.

MontegoMan562 is a Capri RS Owner > zeontestpilot 08/19/2015 at 11:01

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Man it’s been like 4 years.... I want to say it was a bit over 100 to get it flashed. You could call up and just say “Hey what’s it cost to have my PCM flashed?”

MontegoMan562 is a Capri RS Owner > zeontestpilot 08/19/2015 at 11:03

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This is a terrible fucking idea.

He’s recommending you switch to a carbureted system. That would mean losing computer control of the engine all together, buying a carburetor, buying a new intake manfiold (if one even EXISTS for your motor that accepts a Carb).

this would be beyond bad.

Rico > MontegoMan562 is a Capri RS Owner 08/19/2015 at 11:20

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That would be a cool project though!

MontegoMan562 is a Capri RS Owner > Rico 08/19/2015 at 11:24

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Yeah but that would require a lot of time and money, he’s short on both at the moment so it’s spectacularly bad advice.

bryan40oop > zeontestpilot 08/19/2015 at 12:27

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Can’t be done. Unless you spend more than the car is worth, and even then it’s a long shot. Did chrysler still integrate the voltage regulator into the PCM on that model?

zeontestpilot > Brickman 08/19/2015 at 13:08

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Rats...

zeontestpilot > MontegoMan562 is a Capri RS Owner 08/19/2015 at 13:22

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It would be cool, but your right, it would be too much.

zeontestpilot > bryan40oop 08/19/2015 at 13:24

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Not sure... I drive a ‘08

MontegoMan562 is a Capri RS Owner > zeontestpilot 08/19/2015 at 13:27

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Way, way too much. You’d be better off buying a beater car for less money.

I saw a Jeep XJ for sale for 500 on CL the other day that didn’t start. I bet I could get it running for a 100 or so lol.

How’ve you been buddy haven’t seen you around in a while?

zeontestpilot > MontegoMan562 is a Capri RS Owner 08/19/2015 at 21:02

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I’ve been good, haven’t been on oppo too much, I know some people don’t like to hear about my car problems, :/...especially the pt ones. I’m usually on lald, but slim fiances have restricted that fund too.

I wish I could get that jeep. A Cherokee, right?

pip bip - choose Corrour > zeontestpilot 08/20/2015 at 05:18

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no more computers to worry about , but bad for the environment.

realistically though , MontegoMan562 is correct , it’s a terrible idea

it would be a little less complicated , less likely to leave you stranded.

MontegoMan562 is a Capri RS Owner > pip bip - choose Corrour 08/20/2015 at 09:06

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less complicated and more reliable were in fact the only benefits, sorry if that was harsh up there, was just my snap reaction to the idea lol

MontegoMan562 is a Capri RS Owner > zeontestpilot 08/20/2015 at 09:08

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http://detroit.craigslist.org/mcb/cto/517406…

I mean, I think we could get it running under 100 bucks. Is there anything else wrong with it? I don’t know. I do know the going rate for any broken XJ is about 500 bucks though so he’s around the right price.

zeontestpilot > MontegoMan562 is a Capri RS Owner 08/20/2015 at 09:32

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I’m wonder if it’s 4wd or not. Ah, roseville, I grew up in warren, by the border of Roseville.

MontegoMan562 is a Capri RS Owner > zeontestpilot 08/20/2015 at 09:59

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It’s hard to see, but the only indicator of 4x4 on these Jeeps, is the little decal on the quarter panel just under the rear window. I think I see it. If it’s not 4x4 it’s worthless.

zeontestpilot > MontegoMan562 is a Capri RS Owner 08/20/2015 at 10:32

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Very true in the worthless part. Both rwd and 4wd models get 18 hwy mpg, so why even get the rwd?

MontegoMan562 is a Capri RS Owner > zeontestpilot 08/20/2015 at 10:53

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No idea. I’m sure if you have 4x4 engaged it’s not pulling 18 though. Probably more like 12 or 13.

I know those engines are TOUGH though. he can’t get it started my guess is either a bad fuel pump or spark plugs.

zeontestpilot > MontegoMan562 is a Capri RS Owner 08/20/2015 at 11:09

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Yeah, those i6’s are tough. Wish I had the money though, because I do really like the Cherokees.

MontegoMan562 is a Capri RS Owner > zeontestpilot 08/20/2015 at 11:14

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yeah i could probably swing buying it (despite the fact that I shouldn’t as we’re in the midst of a bathroom renovation and need concrete work done to garage and driveway) but my wife’s biggest complaint was “where would we put it”. I said, in the street, who cares it’s a $500 truck?

zeontestpilot > MontegoMan562 is a Capri RS Owner 08/20/2015 at 11:25

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I hear that zeontestpilot guy might be willing to help, as long as he can drive/hoon it whenever. Or course, MrsZtp will say otherwise....

MontegoMan562 is a Capri RS Owner > zeontestpilot 08/20/2015 at 12:30

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MontegoWoman did not seem overly pleased at the idea, no outright no, but not overly pleased lol.

And she’s obsessed with Jeeps!