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CATEGORY LISTINGS > CATERPILLAR > 3126B won't start [ REFRESH ]
Thread Title:

3126B won't start


Created On Monday July 19, 2010 14:23 Diesel Talk
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loggy61
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Note Monday July 19, 2010 14:23 View thread in raw text format
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Have a 3125B military 5ton tractor that won’t start. Disconnected the IAP control, replaced it with new one, replaced sensor and ECM with known good one, replaced heui pump, found lose gear and tightened it and replaced it. Still get no smoke when cranking. Fuel is clean, oil is clean. When we first checked pressure with MD300 it only had 271 lbs pressure, hence replacement of pump. Checked cam timing sensors with known good ones and still get no smoke. Only thing we think we haven’t done is check for injectors leaking, but while using the MD300 we were able to control the IAP valve with the MD300 and it would run. This led us initially to replace the controller. Is there a possibility we got a bad replacement pump? This truck has dual voltage, 12-24volts. 24 volts energize the ecm. Please adviseconfused
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JoeZ
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Note Monday July 19, 2010 16:09 View thread in raw text format
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WOW......the parts man must love you. Talk about throwing a basket of parts at the problem........well anyway.....let's start at the beginning. How did this problem start? I mean from "get" street.....

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 One of the last 2 Stroke mechanics left.
44 years in the business and worked on everything from 53 series to 149 series. Winding it down now...time to move on.
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loggy61
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Note Tuesday July 20, 2010 03:47 View thread in raw text format
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Thanks for your reply. The truck was running fine and all of a sudden it wouldn't start. This tractor doesn't get a lot of action. It mainly gets started and sets with a fuel tanker connected to it ready to go .Very few miles for it's age. The 1st thing we did was disconnect the IAP controller and tried to get it to start. The we connected our test equipment and it gave us the IAP code 164-34 if I remember. Anyway it said injection timing pressure was only 14% or 271 psi. I ran it again today and got the same code and definition. Today I removed the valve cover and no leaks. Engine oil pressure is good while cranking. I checked for voltage at the controller and got 23v. One of the inactive codes was high iap controller voltage. I don't know if that is significant or not. Is there a possibility that the driving gear for the pump is not driving the pump? We plan to pull the pump tommorrow and check for anything we can find.
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desertstormboy
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Note Tuesday July 20, 2010 05:36 View users profile View thread in raw text format
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the gear probably is still loose on the pump. we never have tightened a gear on the old pump...usually we replaced the pump. you need at least 870 psi for idle. did you check the gear that the pump runs off of? you may have damaged the internal gear on the engine itself, but i myself have not seen that before. when you lose the oil from replacing the pump, it usually takes a while before engine gets heui pressure to fire the engine.

-------------------------
 IT WENT BING BANG BOOM!
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Mobiletech
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Note Tuesday July 20, 2010 06:29 View thread in raw text format
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Do you have good oil pressure feeding the heui pump from the low pressure oil pump? Did you check the oil coming from the injectors closely. You may have a bad injector and the deflector on the injector will keep the oil down where its harder to see.
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loggy61
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Note Wednesday July 21, 2010 04:14 View thread in raw text format
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We figured it out, but with a lot of labor. Turns out to be a defective IAP sensor. That was the 1st thing we checked and replaced what we thought was a known good sensor. On top of that the gear was lose on the replacement pump. So that hadto be removed and tightened. Today we removed the front accessory plate and checked the gear. All was tight. Then I disconnected the sensor to get the ECM to default and then it started. Replaced the defective sensor with a good one.Thanks for your help.
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loggy61
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Note Wednesday July 21, 2010 04:16 View thread in raw text format
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It was the IAP sensor as well as a lose gear. Thanks for your input to this problem.
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loggy61
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Note Wednesday July 21, 2010 04:17 View thread in raw text format
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The IAP sensor was bad as well as a lose gear. Thanks
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