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Speedy60 01-10-2013 05:13 PM

92 dakota and me not gonna have hair left
 
Hi all,
92 Dakota, 5.2 L, no start.... Bought for a project that has turned into a nightmare. Had no fuel pressure or spark. Went through these test procedures:
OK, locate the PCM and the 60 way connector and remove the connector. Pull the black plastic shielding off the wire side of the connector to expose the numbering system... it's way better to do it this way than use the Mopar pinout [COLOR=green]diagram[/COLOR].
We'll start with some powers and grounds, so go ahead and turn the key on.
Pin 3 (red/ white wire) is your B+ feed, one that's a suspect in this situation. Your voltage should be basically what system voltage is, supplied through Fuse D of the underhood fuse block (PDC). This circuit commonly rots out from an exposed splice in the left side fender harness, located below the PDC itself, although it sometimes sneaks back enough to be under the washer bottle. Push some amps through this circuit if it shows any voltage at all... if you're blinded by the light, checks OK.
Pin 9 (dark blue) is your ignition switch output. Same test as above.
Pins 11 and 12 (black/ tan) are both power grounds. Reverse your test light polarity and check for good [COLOR=green]power flow[/COLOR] on both circuits,( sued headlamp). Normal resistance to battery negative should be 5 ohms or less, more like one or so. I'm not completely sure where this grounds at this moment, but it may be this puny little 8mm sheet metal screw to the left of the battery. If it's an issue, I'll sure look it up.
With the 60-way disconnected, there should be zero continuity to ground on Pins 6 (violet/ white) and 7 (orange). The #6 pin is your 5v power feed to the MAP, TPS and [COLOR=green]vehicle speed[/COLOR] sensors. With the connector dangling, the sensor ground that completes the circuit is disconnected as well (Pin 4, black/ light blue) so this should be an open circuit. Any short to ground at this point is a harness failure and will take the PCM down instantly. No damage will result from the 5v being shorted, but the PCM will appear completely dead.
Pin 7 is the 8v circuit, supplying the cam and crank sensors. Same as above, with the sensor ground disconnected, it should be an open circuit. Shorting of the 8v will also take the PCM down, but it'll have slightly different symptoms.
Determined PCM was bad, repalced. Now have fuel pressure, and power to coil, still no start and no spark..SO, for "S" and giglles opened the harness to visually inspect splices, form PDC to , well, every where. You can imagine wht the engine bay looks like. Don't have access to a scope, so hooked a noid light into the leads for the coil, noid light lights up for 2 seconds w/ key on, then pulses while cranking. Put noid light into injector plug, get pulse there also.
My question is, is the test on pin 6 and 7 a valid test? I do read resistance in both circuits to ground, but, if I unplug the crank sensor, and the cam (sync) sensor, pin 7 goes open. I even used new sensors to test, and when plugged in, got resisitance.
Also, I have 9 volts going to cam and crank sensors, not 8, am wondering why. I have 5 volts going to tps, map, etc.
I now know why mosta of the drivability guys I know are bald, and drink like fishes..:)
Have done compression test, put engine at TDC and rotor is pointing at # 1 cyl, verified that rotor DOES turn.
New parts so far:
Cam (sync ) swensor
Crank sensor
Distributor cap and rotor
Coil (actually 2 different new ones we had in shop, in case I got a bad 1)
PCM

LATECH 01-10-2013 05:38 PM

Test light should not indicate power and ground at coil terminals when key is turned to on , like a fuel pump prime circuit on a GM.
The ASD is resposible for powering up the fuel pump, igntion coil etc.
IT only powers when the PCM turns it on, and that only happens while cranking or running the engine as it is turned on by the PCM when it sees a cam sensor pulse. The coil ground pulse that fires the coil only triggers with a crank sensor pulse throught PCM . It should never complete the ground path just by turning the system power on.It should remain in a non conductive state until the PCM recieves a pulse from the crank sensor to drive the ground pulse trigger in the PCM
Sounds like another bad PCM.
Also coil drivers in PCMs can sometimes pass enough current to light a test light but wont pass enough current to really drive an ignition coil.

Chrysler PCM s a re pretty junky. I have had them fail right out of the box.
Hard to find a good rebuilt one . Cardone sux.

Speedy60 01-10-2013 06:31 PM

Bad PCM
 
I wondered about that also. I forgot to post previously, when I started this project, had no check engine light. After new PCM, had check engine light, and ASD pulled in, gave me fuel, and had spark for a few "try to start' cycles, with no start. Then, no spark. MY question remains, if pin 7 (crank/cam sensor) has an ohm reading to ground with 60 pin connector unhooked, would this take out a new pcm? Hate to try another one and have same result.....

Speedy60 01-10-2013 06:33 PM

Bad PCM
 
And I'm guessing that is why I have 9 volts to crank/cam sensor instead of the required 8? A bad PCM?

LATECH 01-10-2013 06:37 PM

Do have both the cam and crank sensor unplugged and have a continuity reading? Like less than 1 Ohm?
That will kill the PCM.
If that is the case you can do a wiggle test with an ohmeter hooked up, or split the harness open between the 2 and the pcm.Like the area over the exhaust would be a good place for the insulation to be melted.
It is obviously melted to something on another circuit that has a ground path from the harness, IIRC there is a ground at the firewall at the back of the enginetowards the pass side from center.Maybe it is melted there.
The harness will be grounded at a few places seperate from the PCM.Sounds like you do have a short.

Speedy60 01-10-2013 07:01 PM

Shorts,
 
No, if I disconnect the connector to the cam and crank sensors, circuit goes open, if I reconnect either one I do get an ohm reading, not at shop right now, cna't remember what exactly the reading was, but it was small....

LATECH 01-10-2013 07:14 PM

You need to check each wire . Individually.
Unplug 60 pin and unplug the cam and crank sensors. Then put the black lead of DVOM on ground at engine and probe each wire to the sensors, voltage , return and signal leads, to be sure one of them isnt shorted. They should all read infinite.
9 volts isnt a problem, at least I dont think so. Each component has a tolerance factor or an acceptable amount of deviation from spec. Between that and test equiptment tolerance value, it could read 9 volts.
You can check it against another meter to be sure yours is accurate, or if not, at least how far off it is.
If the wiring checks out, I would have to lean back on a defective PCM from the get go.The coil circuit and its operational conditions you described are not right, and the function originates at the PCM.
Be sure you do not just have a bum coil. Try one off of a running truck, or bolt the one in question on a running truck.

Speedy60 01-10-2013 07:40 PM

Wiring
 
Thank you for your input.. I will try these things Saturday, wifey told me I HAVE to take her to dinner tomorrow night. Gotta keep peace, ya know? I took on this project to keep me busy on the long cold winter nights here in Ohio, guess it's gonna keep me occupied longer than I anticipated......:pain:, I got hooked up on here after reading your help with the girl with same symptoms,,, Your help was extraordinary..... I work as a tech at an indie, I do mostly suspension, brakes and custom exhaust, fuel pumps etc. Your help is GREATLY appreciated. I will get back to you later....

LATECH 01-11-2013 04:47 PM

Thank You and your also welcome. Let us know what it turns out to be as when you post , as you see, others read it and it helps anyone who needs it. Priceless stuff. Good Luck.

Speedy60 01-14-2013 06:29 PM

Things that make you go hmmmmm.....
 
Ok, so I finally got time to work on my project again. Pulled harness from 6 pin connector on drivers side engine to crank/distributor sensor, and all the tranny controls to visually inspect it. No damage visible. On the 5 volt side (pin 6) i get resistance reading to ground with the 60 pin disconnected until I unplug my vss (vehicle speed sensor). Then it drops to almost zero.... Soooo... I decided to plug the pcm back in, and try to start it with the vss unplugged.. No go.... I am still getting a 2 -3 second 12 volt pulse to coil and fuel pump on key up... And I am not supposed to get that... Anyhow... So I disconnected the 60 pin again to do more voltage tests... Guess what? The damn nut that holds the 60 pin came out with the bolt, and looking into the hole it left, there is mucho corrosion etc. falling outta the hole... I am convinced that I got a bad pcm outta the box....Will discuss this with the parts pro in AM, and have a new one ordered.... Will keep you updated....

Speedy60 01-14-2013 06:31 PM

Pcm
 
I did try to get a used part... Because I have heard nothing positive about reman pcm's, but sheesh, they want more for a used part than a reman is gonna cost me..

LATECH 01-14-2013 07:05 PM

Diamond wrecking has one 330-337-3556 $40 bucks. need to get service number from your to be sure

Nicklin Has one 519-822-0301
Route 51 auto salvage has one 724-677-4646
T+M has one 734-397-0000

If those dont match up let me know, I will look a little farther.
Diamond was the only yard in Ohio, the rest are out of state

Speedy60 01-17-2013 04:40 PM

IT's ALIVE!!!!
 
LaTech,
Thank you so much for you help. It is running now. Put in a another reman pcm, and it fired up. So I'm now backing out some of the parts .....sync sensor, coil, which by the way, had a 95 Cherokee in the shop yesterday, it uses same ignition coil, so hooked my original up and it ran fine.....So coil is not an issue...inspected my original crank sensor, it had some heat cracking in it, so left the new one in. I have one lingering question, knowing NOW what I didn't know before about this vintage Dodge systems... I am still getting a 1-2 second 12 volt pulse at the coil on key up... I don't want that to be what fried the original pcm, any ideas what to look for? Or should I worry about it? I thought maybe the pcm was getting some kinda sigbnal return from the sync sensor, so I unbunbled the harness from the pcm to the sync to make sure I didn't have a wire issue.. all is good... Now, I guess I get to use 2 or 3 rolls of electrical tape and put my harnesses back in order.... Fun Fun, Fun...
Again, thanks for your input...

LATECH 01-17-2013 06:24 PM

I cant say the 2 second power up at coil will hurt anything. It is not normal as I understand it. Could be something different in the PCM than what I am used to seeing. I cant honestly answer that.
The ASD relay powers the coil and fuel pump /injectors etc, the ECM controls it, I dont see it hurting anything.
If it is running I would not worry about it.:thumbup:
Glad it is burnin gas again.

stroker_SS 03-04-2013 11:11 AM

Very cool, I love seeing threads actually being resolved!:D


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