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Discussion Starter #1
First off I've had this truck for about 7 years .. Only trouble I've had was in early spring I put a cam sensor on it to fix the tach ...
Truck is a 2001 DRW 3500 the engine has 117 thousand km on it .. (about 70 thousand miles) .. Over the last month it hasn't started about 6 times , it just turns over and won't start ... And I know when it isn't going to start , soon as I turn on the key I watch the "wait to start " light even if the truck is hot the light comes on for a second the system must be checking temp etc. ...Anyway if that light doesn't flicker on for a second that truck will not start , I have to cycle the key several times watching the light .. 1 time (at home) I got tired of cycling the key and had to wait about an hour then it started ..

Any ideas, to me it seems like maybe a relay ..
 

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It is your ecm plus you need to check tou alternator for ac voltage this is what is taking out your ECM that ac voltage is hard on all your electronics when your wait to start light doesn't come on the ECM isn't booting up to communicate with pcm and all the sensors if you have ac voltage you want it to be .05 volts ac if above replace alternator and check new alternator because it could be putting out to much ac voltage if it is return it until you get one that measures less than .05 volts ac
 

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Discussion Starter #3
Where and how do you check that ..?
 

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Discussion Starter #4
But the alternator isn't putting out AC until the engine is turning over, I know the ECM changes the AC power to DC power to change the batteries .. But I have to watch the "wait to start" light before turning the engine over to start , if the light doesn't come on for a second and go out then it will not start .. When the truck is cold it always starts the "wait to start" light usually comes on and stays on several seconds , but when hot the light only comes on for a second and like I said sometimes you have to cycle the key from off to on quite a few times before the light comes on for a second ..

I forgot to add the truck is a manual transmission ..
 

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Check fuse 3 in the under hood box real good. Use test light or volt meter and pull it out too and inspect it closely. The main power for the ecm is off of this fuse.
 

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NO the ECM does not change the ac to dc, that is done by the rectifier in the alternator. That failure is what damages the ECM. You can get it going with another ECM only, but you need to repalce the alternator with one that with AC below .03 to .05v. to prevent also killing the new ECM. Used ECM's are plug an dplay but must be the same PN as the old one. NOt all years match98-00 wont fit 01/02 at all wiht out programmingIt is not the fuse. When it goes out intermittently and won't start until more that one try or a long wait for the light is the ECM going bad and that is usually how it happens overtime. Then one day it will die completely.
 
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Discussion Starter #7
I'm not saying your wrong because I don't know ... But the 2001 shop manual that I downloaded from this site says it uses an electronic voltage regulator within the PCM

section 8F-27

CHARGING DESCRIPTION
The charging system consists of:

Generator

Electronic Voltage Regulator (EVR) circuitry within the Powertrain Control Module (PCM)

Ignition switch (refer to Ignition System for information

Battery (refer to 8, Battery for information)

Battery temperature sensor

Check Gauges Lamp (if equipped)

Voltmeter (refer to 8, Instrument Panel and Gauges for information)
Wiring harness and connections (refer to 8, Wiring
 

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@bigfish95971 is right. 100%
Voltage regulation is different than ac-dc conversion. The PCM regulates the voltage and the rectifier diodes filter change AC to DC. You need a good multi meter that reads AC milliamps. Red lead goes on the alternator charge lead and black to ground. Now read the value. If it's above .05VAC the alternator is putting out too much dirty power, ie AC noise. The electrics on these trucks were not that great from new and they can't handle much AC until everything computerized starts to fail. I'm not a good typist so that's all I'll say but there are a TON of threads on this subject here and over on moparmans forum.
 

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Here's one for starters

 

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I have no idea how to edit a post with this confusing new format they went to. In my above post #8 I typed 'filter change'. I meant to type just change. Disregard 'filter'.
 

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I have no idea how to edit a post with this confusing new format they went to. In my above post #8 I typed 'filter change'. I meant to type just change. Disregard 'filter'.
You click the 3 dots on the right side, that is where the edit functions are.
 
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Jake, Close but,
Rectifier Converts AC to DC, not filters. PCM regulates charge rate in volts according to load and need read by battery temp and load. Volt meter needs to read low voltage(mili-volts, not mili-amps, that is why on many meters you need one with a 2v scale, some medium quality meters will not read that fine on higher scales. $6 ones will not at all.
 

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Yeah, like I said in post #10 I don't know how to edit a post. Thanks to maxwedge I do now.
 

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That is fine I took me asking to find it too.
 

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Test your alternator and send your ECU off to the ECU rebuild shop in Key West ($200 or so for a rebuild)
 

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If it comes down to you needing a new ECM I have one for an 01'
 

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Discussion Starter #17
I did the ripple test by watching a video by (I think the name was mopar1973 I think .. ) Anyway his test showed alternator to battery was .033 VAC .. on mine it was .026 VAC .. His test at the battery was .013 VAC mine was .036 VAC .... Does that sound good or bad ...?
 

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It sounds like AC is OK but all ECM failure is not due to AC, just a lot are. That makes you lucky as no alt is needed. But a good battery terminals cleaning should mmm be done. However ALL wait to start light failure is always ECM FAILURE.
 
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