P1689 - 1999 Ram 2500 - Idle @ 800rpm & start easy- touch pedal rpm jumps to 1400????

[balesray]

Found this trouble a couple of places but no for sure solutions.  Mileage on truck is 87,453 and is stock all the way.  No trouble in the past.  Just Oil, filters, tires and battery.  Bought new in late 1999. Old and retired but I like my truck and need to fix it soon so help.  Replaced the lift pump and filter, checked the APPS voltages and are OK,  engine starts quick and idles perfectly.  Touch the accelerator pedal and rpm jumps to approx. 1400 and that is all.  Foot off pedal, goes back to idle.  MIL (engine light) on & all other lights work normal.  Wait to start on and times out as usual.  Code P1689 is all that reads.  HELP PLEASE.

[Me78569]

Here is the article we have on that code

 

 

 

 

Our trucks are extremely susceptible to electrical issues.  I would go through the engine bay with die electric grease and clean and apply to every plug under the hood.  Clean all battery cables and grounds. 

 

 

Next check the plug on the back of the vp44.

 

 

Does your wait to start light come on as soon as you turn the key from off to run?

[balesray]

Wait to start light comes on as soon as the key is on and times out as usual.  Have checked and cleaned most of the grounds but not the ones on the passenger side that have plugs.  Couldn't get them apart.  Checked the vp44 plug and ecm plug and no damage and plenty of grease. Wiring checked OK also.   New batteries couple months back and cable connectors are clean and tight.

Read the article mentioned above and have about decided it is probably the ecm but would like to be sure if possible so looking for ideas.  Eight hundred plus is hard on us old (77) retired deplorables. 

Will go back to the ground cables connectors with more determination.    Sure appreciate your time.

[Me78569]

I wouldn't jump on the ECM dead thing quite yet.  Normally we would see other issues.

 

 

I would use a multimeter to check all the plugs / wires between the ECM and VP44 for shorts. 

 

nick 

[balesray]

Used a Fluke 77 to check continuity and shorts on wires from ECM and VP44 plugs and all checked OK except there is no connector in pin 9 off the VP44 connector.  Schematic does not show a pin 9 so I assumed that was OK for it not to exist.  Pain in the butt to get that ECM connector off but everything looks good. 

Still haven't gotten the ground connectors apart.  That's next hopefully.  more suggestions please.  ????

Ray

[dripley]

Are you still on the original VP? And are you still running the stock style lift pump? The reason I ask is my original VP went at 75k though it acted differently than yours. My ECM went at 217k and one of the symptoms was as you described. Do you know anyone you could borrow an ECM from to swap out and see what happens? Both the ECM and the VP are pricey parts to buy and throw at the problem without being sure.

By the way Welcome to the forum.

[balesray]

Original VP, ECM and had original lift pump until this problem.  Replaced the pump with oem original from Rock Auto along with filter.  Old pump was still working but someone said the problem was probably the pump. 

No friends with a diesel and live in no-mans-land.  Closest Dodge shop about 50 miles. 

Seems everything that goes on these trucks are pricey so will have to go back to pinto's if have to buy either of those items.

Wife says it was a lightening storm that went through a few days before the trouble.  Problem with that is she is usually right so I need to find something simple like a loose wire.  Have checked for what might be bad or broken wire but no luck.  Thank and hope don't get to be to much trouble.

Ray

[dripley]

The oe lift pumps were not a great design. They are notorious for not providing enough pressure for the VP causing them to fail. I did not learn any of this until after I lost my ECM and joined this forum. With only 87k on the truck and if the rest of it is in good shape either of the parts, while pricey, is a small price to pay to keep it on the road. But if it turns out to be the vp a new fuel system would be in order. At least a FP gauge so you can keep an eye on that OE pump pressure. And if it turns out you do want to sell it, you would have no problem doing that.

 i would love to see 87k again. I am just 299k beyond that.

[balesray]

Don't want to sell.  Got an offer  couple month ago for $12000 cash and guess will have to go for the expensive stuff.  Wish knew for sure if it is the VP or ECM.  My luck will go the wrong way.  Love my truck.

[dripley]

I love mine too. I would hate to see you driving a Pinto.

[Mopar1973Man]

Check your alternator AC noise voltage and see how much your making. 0.01 to 0.03 AC volts is normal above that issues start to grow. 90% of all ECM problems stem from bad alternators.

[balesray]

AC noise on alternator ranges from .025 to /.030 ACV.  Also checked and cleaned the last two ground wires although they looked good.  Keep them coming and I will check them and thanks.

[balesray]

Does anyone have the electronic schematic of the inside of the ECM along with what the signals look like on a O'scope  and their amplitude.  I have the equipment and know how to use them if I could get a copy of the schematic.  I have a copy of the wiring diagram of truck but no info on the type signal or strength from sensor or between the ECM and VP44.  Will buy the info if it is available.   Thanks everyone.

[Mopar1973Man]

Sorry, there is no information on the internal part of the ECM that I know as of right now. 

[balesray]

Just wondering what all the sensor inputs that feed the ECM actually do and what effect they have on the operation of the engine.

There is an article on Diesel Bomber with the same problem I have.  He followed typical suggestions and replace APPS, ECM, VP44, lift pump and filter, checked all the wire and pulled the wiring harness,  checked all grounds and every time he cranked it up the same problem is still there.  He finally gave up and parted the truck.  I don't want to go through the same nightmare & would like to determine what is the cause of this problem without simply guessing that maybe that is the problem.  So logical ideas that can be checked to determine the actual problem will be greatly appreciated.  Thanks for your help.

[Me78569]

I am all but sure the issue lays in either the VP44 or the ECM.  since you have the 1689 code I would be concerned that you have an ecm issue.

 

You can watch for canbus messages to be sent from the ecm to the vp44.  Here is showing what the message looks like.

http://www.warwickcontrol.com/download/reference/Tech Tip 3.pdf

[balesray]

Thanks for the info.  The  signal from ecm to vp44 is only .4 volts and according to warwick it should be 2 volts peak to peak so looks like I need an ecm.

Any suggestions where to get one and is there a dependable place to have this one fixed.  Several places on the web but would like some advice on a trusted site.

 

 

 

Edited October 17, 2016 by balesray

[Me78569]

If you care to try something that may or may not work. I guess at this point you don't have much to loose.....but,

 

Quote

If you 'brick' the module, there is a special 'recovery mode' that can only be activated if you can get the APPS input and the Oil Pressure inputs to go high (+5 volts) at the same time, before you switch the key on. This isn't something you could normally do, but on the bench it's easy. 

 

 

That was from a guy that got pretty deep into the ecm code.    It might somehow fix your issue..... doubtful, but you won't be any worse off if you already need a new ecm.

[Mopar1973Man]

Personally the ECM is damaged most likely from excessive AC noise from the alternator. If you do replace the ECM make sure to test that alternator for excessive AC noise before starting the engine with the new ECM.

[balesray]

 

Any suggestions where I can purchase an ECM for my truck that has a reasonable price.