After 7,000 flawless miles on this 'new to me' discovery, I went to start it up this morning and it cranked for a really long time before it started, now it idles like normal for a while, then stumbles from 750 RPM down to 600-500rpm. Once or twice it stalled.
I checked the water separator, no water in there. No check engine light.
Planning on leaving for a short trip this afternoon, now I'm concerned.
Thoughts?
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Sounds like the it could be a HUIE pump failing. I had similar symptoms when we were in Homer AK. I hope it is something simple.
A diesel mechanic can check the pressure out put to determine if all is OK. I know there are some article in this forum that talk about installation of a filter to help prevent future failure consequences down stream of the HUEI pump after replacement. If it is the HUIE pump I would strongly suggest installing the filter as a preventive measure.
This is the article I ref. "New Measures to Protect Your HEUI Pump"
Before going after the heui pump, there's a IAP Sensor that can get plugged with sludge which ends up with the system sending incorrect pressure to the injectors. This can make a hard/no start or run rough condition. An easy way to determine if it's the senor is to unplug it and try to start the engine. If it starts and runs, it's the sensor. From what I understand, you can remove the sensor, flush it out and re-install. Before any testing is done on the heui pump, check the sensor first.
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Tom and Pris M. along with Buddy the 18 year old Siamese cat
1998 Safari Serengeti 3706, 300HP Cat 3126 Allison 3060, 900 watts of Solar.
Dragging four telescopes around the US in search of dark skies.
I'm late to the party on your issue .
Some info you might find useful.
The C-7 and 3126B & E engines are similar to the point the pdf info is useful for both.
When replacing the sensor , do not over torque or you'll damage the seal ( O ring ).
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99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
Thank you everyone!
The IAP sensor was the issue. $160 at Freightliner Northwest in Pacific WA.
If you have this issue, note that the new sensor has 6 sides, 15/16",
But the stock one is round, so I didn't have the right tool with me to take it out. Vice grips had to take it out. Fortunately it's not torqued in hard, it's machine threads with an O-ring seal. (Freightliner NW gave me an O-ring automatically, it's a separate part)
Poor access makes it tough to get a wrench to it, but it's do-able to sneak the wrench in through the wires and tubing.
Be careful to clean the area around the sensor thoroughly so paint chips and dirt don't get into the hole while the sensor is out.
Here's one from the top . Yellow circle .
and a diagram side view.
OK , I guess I should have been more specific , yellow circle is the IAP sensor , red circle would be the spot where a manual lift pump would have been mounted ; probably removed to allow lower clearance in the engine bay as it mounted at a 45 degree angle .
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99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
A picture of the sensor and access sure would be nice.
If you have not done this yet you should open up an account with Cat on line parts. You can put in your vin number look up your parts. It provided part diagram blow ups and you can price all the parts you need. the price on line is the same as you pay going to the parts counter. I often order them on line and go in and pick them up. Also once your in the system they email you sales info. like when they have a sale for filters 20 or 25% off. If your a DIY guy like me this is the way to go.
I've read that some people carry a spare sensor. There have been cases of mechanics changing out the Heui pump for thousands of $$$ only to discover the old pump was fine and the problem was the $150 sensor. Unplugging the sensor to test it should be the first step before assuming it's the pump. It's a test even the coach owner can do if they have similar symptoms. Cost=$0
I've also read of people removing the sensor and cleaning it out with brake cleaner as a on-the-side-of-the-road fix.
Glad that's all it was. Phew!
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Tom and Pris M. along with Buddy the 18 year old Siamese cat
1998 Safari Serengeti 3706, 300HP Cat 3126 Allison 3060, 900 watts of Solar.
Dragging four telescopes around the US in search of dark skies.
Linear Mode
