3216E no start

[gauto5150]

Hey everyone,
I have a 2004 Discovery 39J and we took a 6 hour trip to St. Louis right before Halloween. The engine ran normally there and almost all the way back. For about the last 80 miles my battery light came on and off, I had a low charging voltage. It was night time, with the TV on for the kids, headlights, and both heaters. So I fired up the generator and it kept the charge on the house and chassis batteries. This has happened to me before so there was no surprise. I have about 75K on the chassis and this will be the 3rd alternator.
When I got of the expressway and was in more stop-n-go driving, the idle was surging very rapidly. The frequency of the surge was about 150 RPMS about 2 times per second. You feel it when stopped at a light. No fluctuations in oil pressure or anything else other than dips in the charging volatage, it was very strange.
I parked it at home and made plans to replace the alternator with an upgraded 200 amp style as opposed to the original undersized 140 amp.
But now, it cranks and will not start. The chassis batteries are older and it didn't have the cranking speed I normally have. But, it has started under slower cranking speeds in the dead of winter before.
I've read on the forums that the injection actuation pressure sensor sometimes will cause this problem of no start out of the blue. I've heard you can unplug it and it will go into a default mode allowing the injection pump to operate.
If anyone has any thoughts or suggestions on this I would greatly appreciate it. Thanks

[gauto5150]

UPDATE: It does emit white smoke while cranking and it'll hit on a couple cylinders after an extended crank but doesn't start. I have the block heater on and I've cranked it multiple times so the cylinder temps should be warm enough to fire. It's 45* here as of now.

[gauto5150]

ANOTHER UPDATE:
It started after a few more tries, ran like it was hunting for idle. It cleared out and the Check Engine light illuminated. It barely has any throttle response, it appears to be in a "limp mode". I drove it to my shop after it ran for about 30 minutes, I shut it off once it was inside and didn't start after that. I'll try to get the codes out of it and post what I find.

[gatorcq]

It sounds like you have fuel pressure regulator, pump or the HEUI is bad.
Yes the IAP sensor can become erratic, and cause a shut down. Yes you can unplug it (if bad) start - limp mode. By the way, your #1 post, maybe it was NOT the alternator, but engine issue.

I do hope it is not the HEUI.

[gauto5150]

I had a voltage drop with the inverter on and the accessories running. This isn't my first alternator rodeo, I've rustled a couple of those throughout the years. They're built undersized so they fail prematurely in my case. The last 2 were of "suspect" quality as well so it doesn't surprise me that it failed.
Does anyone know how to manually pull the engine codes out of this Discovery? I have seen other trucks (NOT RVs) use the cruise controls, I have tried that with no luck.

[gauto5150]

UPDATE:
I unplugged the IPR and it started. From what I have seen, the 3126E is a combo of the 3126B and the C7. I found the part number 224-4536 caterpillar. Unplugging the IPR defaults the reading to 1200psi I believe. It needs 850psi to start.
I am going to change it and post results.

[gatorcq]

IAP you mean ?

[megehrs]

Update.....I let it sit overnite in parking lot in Searchlite, NV. What choice did we have? This morning I started generator. Ran block preheat for ten minutes. Gave it a crank... spun over okay but did not start initially. Used MON switch for more juice. Got it started but it would only hold 600 rpm and no throttle. Died once. Started it again. Still held only 600 rpm. No throttle. Let run for about 10 minutes. EVENTUALLY it found itself and ran properly. Now ideling well with normal throttle response. Will let run 30 min before we bolt for winter stop in Bullhead City. My only guess is that I had air in the fuel lines from all the jockeying I did last nite trying to get the toad to back up and then disconnected entirely. All of that was in a sloping parking in nothing more than idle. Anyway, that is my story and I am sticking to it. Thanks to all for the helpful posts.

[gauto5150]

I changed the IPR or IAP sensor. (Terminology differs depending on who you talk to)
Fired right up like new. It hasn't started that well in about 40K miles. Drove out great as well. Cost about $76 from a CAT supplier on ebay.

[megehrs]

Can you tell me where the IAP sensor is located on the 3126? Mine has started several times while we are wintering, but I may need to know what it looks like and where it is located on the engine for the "next time". I may look at buying one to have around as well.

[JEEPOHOLIC]

I believe its on top of the head, drivers side towards the front, I replaced that one and the one one HEUI and its on the back side of it, both are very easy to replace, before I replaced those 2, I had no power and would stall when it came to a stop, mine is a 3126b motor in a Freightliner FL-60 Sport Chassis

[gatorcq]

You are welcome

[gauto5150]

Originally Posted by megehrs

Can you tell me where the IAP sensor is located on the 3126? Mine has started several times while we are wintering, but I may need to know what it looks like and where it is located on the engine for the "next time". I may look at buying one to have around as well.

http://www.irv2.com/forums/attachmen...8&d=1391963362


Here's a picture showing where some of the sensors are located. Mine was on the passenger side because it's a rear engine chassis. But in the front engine, it would be on the driver side.

[gauto5150]

Originally Posted by gatorcq

You are welcome

You are thanked...