ecm bad?
06-11-2005, 11:31 AM
#3
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Originally posted by Begle1
Err, your truck doesn't have an ECM, so I'll bet yours isn't bad...
Err, your truck doesn't have an ECM, so I'll bet yours isn't bad...
I know my '92 has an ECM, and I believe they started with the 91.5 models. The ECM doesn't control as much as on the gassers, but the charging system, overdrive, speed control, and a few other things rely on the ECM to function.
Swank - What symptoms are you having?
06-11-2005, 11:44 AM
#4
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i'm trying to hook up a tach, and getting funky signals at the connection for the sensor at the front of the head. also, i was told that if your crank sensor doesn't work, your alt won't charge. mines been burnt out for quite some time, but i have no charging issues. i replaced it a couple weeks ago and did some fooling around trying to get it hooked up to the tach i have and burnt that one up too. there is a 3 prong connection at the front of the head. one has 4+ volts, one has 11+ volts and one has zero. supposedly, those wires go to the ecm and the ecm sends a signal to the underdash harness? at the harness, 3 of the 4 prongs are grounded with ign off, 2 are grounded with ign on. 
. the other problem is that this sparky stuff is waaaaaaaaaaaaaaaaaaaaaaaaaaaaaaay beyond me. and i don't have a manual. i found some schematics, but that's greek to me, AND was told that they aren't what's actually under our hoods???? i'm about to let this one slide, but i really want a tach hooked up. oh yeah, this is the tach i'm trying to use. thanks.
dave
. the other problem is that this sparky stuff is waaaaaaaaaaaaaaaaaaaaaaaaaaaaaaay beyond me. and i don't have a manual. i found some schematics, but that's greek to me, AND was told that they aren't what's actually under our hoods???? i'm about to let this one slide, but i really want a tach hooked up. oh yeah, this is the tach i'm trying to use. thanks.dave
06-11-2005, 11:50 AM
#6
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Well, that's your probelm right there - it's not the right tach. If you want a tach that works with the factory harness, the only ones I know of are the Mopar tach (discontinued 
) and the Isspro.
Have somebody hook your truck to a scan tool, if the PCM is getting a crank sensor signal they will be able to read RPM on the scanner.
The AutoMeter 2888 tach is really easy to hook up.
) and the Isspro.Have somebody hook your truck to a scan tool, if the PCM is getting a crank sensor signal they will be able to read RPM on the scanner.
The AutoMeter 2888 tach is really easy to hook up.
06-11-2005, 11:51 AM
#7
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From the 1st Gen FAQ:
Question: Is it safe to put an aftermarket tach on?
Answer: No problem at all. The 89-90 trucks need the crankshaft sensor. 91-93 trucks already have the crankshaft position sensor on your crank dampner. You see that wiring harness coming off of the dampner? Thats what it is. These were already wired for an aftermarket tach. The end of the wiring harness is right underneath the steering column in the bundle of wires that leads to the fuse box. It should be a 4 pin flat style connector. Isspro makes a kit that hooks up to this existing wiring harness. Takes about 5 minutes to hook up (not including gauge mounting time).
Update* The Isspro kit needed is R8912-92
Truck 4 pin connector / Tach Sensor End
Black To Black (GRD)
Orange To Green Lamp (Pos)
Black To Red (DC POS)
Grey Lt Blue To White(Signal)
By: Monty
Answer: No problem at all. The 89-90 trucks need the crankshaft sensor. 91-93 trucks already have the crankshaft position sensor on your crank dampner. You see that wiring harness coming off of the dampner? Thats what it is. These were already wired for an aftermarket tach. The end of the wiring harness is right underneath the steering column in the bundle of wires that leads to the fuse box. It should be a 4 pin flat style connector. Isspro makes a kit that hooks up to this existing wiring harness. Takes about 5 minutes to hook up (not including gauge mounting time).
Update* The Isspro kit needed is R8912-92
Truck 4 pin connector / Tach Sensor End
Black To Black (GRD)
Orange To Green Lamp (Pos)
Black To Red (DC POS)
Grey Lt Blue To White(Signal)
By: Monty
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06-11-2005, 11:53 AM
#8
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Thread Starter
Originally posted by wannadiesel
Actually it's a PCM.
Are you able to get trouble codes or do you have a situation where nothing that's run by the PCM is working?
Actually it's a PCM.
Are you able to get trouble codes or do you have a situation where nothing that's run by the PCM is working?
i have nooooooo idea dave. i don't know how to get trouble codes and i don't know what the pcm runs. i don't have a speedo because i don't have a sender, so i don't know if the cruise control works or not (i'm just guessing that the cc needs some input from a "higher power"). my AC doesn't work cuz i ripped it out, but i ripped it out because it didn't work.
. i don't have any problems with a lack of charge or anything. other than that, i just dunno.dave
06-11-2005, 12:00 PM
#9
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Just slap the Autometer 2888 alternator tach on there and get on with your life, then. 
If your heater grids and WIF light still work, the PCM is probably OK. The bad charging system and no A/C is probably due to a bad or misadjusted crank sensor, or possibly a bad connection in that circuit. The PCM always thinks your engine hasn't started yet.
Cruise and speedo are a VSS sensor problem. The speedo is not dependent on the PCM, as long as the VSS is working the speedo should work.
If your heater grids and WIF light still work, the PCM is probably OK. The bad charging system and no A/C is probably due to a bad or misadjusted crank sensor, or possibly a bad connection in that circuit. The PCM always thinks your engine hasn't started yet.
Cruise and speedo are a VSS sensor problem. The speedo is not dependent on the PCM, as long as the VSS is working the speedo should work.
06-11-2005, 12:00 PM
#10
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Thread Starter
Originally posted by wannadiesel
Well, that's your probelm right there - it's not the right tach. If you want a tach that works with the factory harness, the only ones I know of are the Mopar tach (discontinued ) and the Isspro.
Have somebody hook your truck to a scan tool, if the PCM is getting a crank sensor signal they will be able to read RPM on the scanner.
The AutoMeter 2888 tach is really easy to hook up.
Well, that's your probelm right there - it's not the right tach. If you want a tach that works with the factory harness, the only ones I know of are the Mopar tach (discontinued
) and the Isspro.Have somebody hook your truck to a scan tool, if the PCM is getting a crank sensor signal they will be able to read RPM on the scanner.
The AutoMeter 2888 tach is really easy to hook up.
i bet that am 2888 is easy to hook up. i just had a hard time finding one for $20.
06-11-2005, 12:01 PM
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Originally posted by swank
i don't have a speedo because i don't have a sender, so i don't know if the cruise control works or not (i'm just guessing that the cc needs some input from a "higher power"). my AC doesn't work cuz i ripped it out, but i ripped it out because it didn't work.. i don't have any problems with a lack of charge or anything. other than that, i just dunno.
dave
i don't have a speedo because i don't have a sender, so i don't know if the cruise control works or not (i'm just guessing that the cc needs some input from a "higher power"). my AC doesn't work cuz i ripped it out, but i ripped it out because it didn't work.
. i don't have any problems with a lack of charge or anything. other than that, i just dunno.dave
To check the codes, cycle the ignition key "on-off-on-off-on" and watch the "check engine" light. It will flash out the codes (flash-flash-delay-flash-flash would be 22). If no trouble codes are stored it will give a 55. I'm guessing there will be codes due to the lack of a speed sensor, and maybe even some related to the AC system.
EMC, PCM, ECU...every manufacturer calls 'em something different. I just call 'em "PITA."
06-11-2005, 12:07 PM
#12
Adminstrator-ess
Your tach is designed to work with a magnetic pickup, it's sending voltage out on the signal wire, and it's not designed to be fed voltage from the PCM on that wire. The Isspro is passive like a gasser tach.
I think the PCM sends 4 pulses per rev. to the harness, but I don't know it for a fact. Voltage is probably around 5 volts, that's typical computer sensor voltage. I went with the AutoMeter because it matches the rest of my gauges, so I've never messed with the tach harness.
I think the PCM sends 4 pulses per rev. to the harness, but I don't know it for a fact. Voltage is probably around 5 volts, that's typical computer sensor voltage. I went with the AutoMeter because it matches the rest of my gauges, so I've never messed with the tach harness.
06-11-2005, 12:08 PM
#13
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Thread Starter
ok. i'll throw in the towel. thanks for the help guys. actually one more ? though. if my battery's been disconnected for a while, will it still have codes? and if i get a 55, will that mean all is well?
06-11-2005, 12:10 PM
#14
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The codes should go away, but I bet you'll get some once you drive it again.
If you don't plan on putting the A/C back in, there's really no need to fix whatever's wrong with the crank sender. I know this sort of thing is not your favorite kind of truck work.
If you don't plan on putting the A/C back in, there's really no need to fix whatever's wrong with the crank sender. I know this sort of thing is not your favorite kind of truck work.
06-11-2005, 12:16 PM
#15
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Originally posted by wannadiesel
The codes should go away, but I bet you'll get some once you drive it again.
If you don't plan on putting the A/C back in, there's really no need to fix whatever's wrong with the crank sender. I know this sort of thing is not your favorite kind of truck work.
The codes should go away, but I bet you'll get some once you drive it again.
If you don't plan on putting the A/C back in, there's really no need to fix whatever's wrong with the crank sender. I know this sort of thing is not your favorite kind of truck work.
ahh. right. because the 2888 is an alternator tach huh? dangit, i just bought a new cps off ebay. oh well. thanks for the help wd. i appreciate it. and you couldn't be more right about how much i like this kinda shineola. wait till you see my new airfilter though. THAT was fun.
dave