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Thread Title:

3126 cat running poor

Created On Thursday July 08, 2010 13:06

MotsTowing

Posts: 5
Joined: Jul 2010

Thursday July 08, 2010 13:06

Truck came into the shop running poor surging under full thortle and some times lacks power replace transfer pump filters where also done .this is a 3126 cat in a 2000 6500 chevy I dont have a scan tool with software in it for this truck but before i say bad injection pump was wondering if anyone has a few ideas . MY injection service guy doesnt bench test cat pumps anymore so iam kinda stuck a little any help would be great

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Mots Towing and Repair

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JoeZ

Posts: 938
Joined: Dec 2008

Thursday July 08, 2010 13:32
Do the obvious first.....check fuel pressure on the outbound side of the secondary fuel filter. ------------------------- 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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MotsTowing

Posts: 5
Joined: Jul 2010

Thursday July 08, 2010 13:41
what should the pressure be ? I did just put the new cat transferpump on to day still runs the same surging and not holding steady rpm ------------------------- Mots Towing and Repair

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JoeZ

Posts: 938
Joined: Dec 2008

Thursday July 08, 2010 15:09

I could be off....but a guess would be 20lbs at idle and 60-70 at high RPM. Check for air bubbles in the return line. The pump you changed rarely goes bad.....most times it is the check valves that go bad or the fittings on the plastic lines that draw air from the tank. We have changed many lines on GM trucks with 31XX series engines. Most times I have had an engine surging at full throttle, it has been air in the fuel system.

-------------------------
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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JoeZ

Posts: 938
Joined: Dec 2008

Thursday July 08, 2010 15:17

By the way.....The GM service manual says to completely bleed the air from the system, remove the return line from the tank. Connect an air line to the fitting you just removed the line from, put the return line in a container, start the engine and pressurize the tank. You need to have a pressure regulator on the air line going into the tank. When no more bubbles are present, reconnect the return line.

-------------------------
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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desertstormboy

Posts: 372
Joined: May 2008

Thursday July 08, 2010 19:25

thats why i dont like shadetree mechanics tinkering with the newer type engines. Most of em dont have the capabilities to do certain tests and have no clue what you are talking about when you tell them the actuation pressure sensor should be showing the same on ET as on a manual gauge. I have seen the controller be at fault a lot of times, but you would have to do the step test to check it properly. if it shows more than 64% output, usually it is bad. like joe said, i have never had to change a fuel pump. most of the time the springs are broken in the check valves and ruin the pump. if the fuel pressure is not up to par, most of the time it is the check valve in the back of the head or the plastic fuel lines that run up to the pump. not to be rude, but your name says it all mots TOWING, not mots caterpillar repair. good luck. TOW it to a cat dealer.

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IT WENT BING BANG BOOM!

Edited: Thursday July 08, 2010 at 19:26 by desertstormboy

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MotsTowing

Posts: 5
Joined: Jul 2010

Thursday July 08, 2010 20:56

thanks joe for the help as for the other guy that put his 2 cents in Iam just asking for a few tips as i have been out of the heavy truck side for some time iam a A tech not just some clown that opened a towing bizz. I did work on heavy trucks for years just got out 2 years ago I run a fleet of wreckers and rollbacks but far from a shade tree tech as you say If you can be help full keep your comments to your self thats why I stay off of foums like this there is alway the guy who thinks hes a know it all and is the god ..... Joe I was woundering about the IPR could cause this thing to do what i describe .as to why I replced the transfer pump there was fuel that was damp around where it bolts to the pump

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Mots Towing and Repair

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desertstormboy

Posts: 372
Joined: May 2008

Friday July 09, 2010 04:08

well if the pump was damp,,doesnt mean pump was bad, means the oring was not sealing. and yes the controller could cause this, but to check it, you have to have et to perform the proper test. all im saying is if you dont have the proper equipment to troubleshoot and perform tests, then you just throwing parts at it and costing the customer a lot of money that is not needed and probably wont get their business anymore. anyone can exchange parts.

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IT WENT BING BANG BOOM!

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JoeZ

Posts: 938
Joined: Dec 2008

Friday July 09, 2010 04:43

Well, MotsTowing, it's like this.....we try to help one another here. Sometimes it's obvious the person that needs help is just a little short on knowledge and equiptment to do the job properly. We can still help but only up to a point. I have to agree with desertstormboy that just throwing parts at the job is the wrong aproach. A few simple tests would have shown you that the pump was probably not your problem. I gave you some basic idea's of where to start. desertstormboy backed up what I said from his experience.

The next thing I would have liked to hear from you is that you tried my suggestion and it either worked or not. You threw out another question and if you feel that you found the problem it being the "IPR" as you put it, by all means change it.....and I'll step down from the plate and you are on your own. Good luck.

-------------------------
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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MotsTowing

Posts: 5
Joined: Jul 2010

Friday July 09, 2010 06:42

well thanks joe for the help ipr fixed the truck this morning. like i said before this is why i done get on free fourms I just dont have time for other peoples comments I just havent worked on many newer cat motors mostly jap crap thats what we have here in are fleet and gas motors but thanks again and yes your right with out a scan tool it makes it real hard to do anything any more on this stuff but this was a truck travling just trying to get him on the road thanks again

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Mots Towing and Repair

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JoeZ

Posts: 938
Joined: Dec 2008

Saturday July 10, 2010 07:16

That's a new one on me....I have never had to replace one. Usually we just put a kit in it and it is fine. I'll bet your customer wasn't too happy after paying for a new supply pump and and new IPR valve. Not to be a smart ass here, but in this case your customer would have been better having it diagnosed as being the IPR valve. Cat would have thrown in a kit and he would have been on his way in a few hours.

-------------------------
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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desertstormboy

Posts: 372
Joined: May 2008

Sunday July 11, 2010 06:47

thanks joe. i myself will help anyone to the best of my knowledge, but when a guy is not properly equipped and dont have the knowledge its kind of hard to properly give the information needed to troubleshoot the problem. another thing IPR? we had a tow company that sometimes would tow a truck to our shop, we would fix it, the tow company would pay us, then charge the customer. im not in the forum to run away people, because sometimes we learn a lot ourselves from other comments about problems and troubleshooting techniques. once again thanks.

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IT WENT BING BANG BOOM!

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MotsTowing

Posts: 5
Joined: Jul 2010

Monday July 12, 2010 08:56

well iam guessing with all ???? after IPR I will not ask for anyones opion on here seem the cat dealer had no problem with finding the part when I told them I needed a IPR . Like I said in the last post hate free sites . there are a bunch of know it alls on here. Like I said in the passed Iam a A tech not some clown that just started doing this 25 years in the bizz . Just not up on the cat motors we see alot of jap and cummins stuff . not being a smart ass but thats the way it comes across deasrtboy trucks fixed charge a fair price guys happy thats all that matters in the end. Have a Good life will not post on here AGAIN thats for sure!!!

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Mots Towing and Repair

Edited: Monday July 12, 2010 at 08:58 by MotsTowing

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Mobiletech

Posts: 94
Joined: Jun 2010

Tuesday July 13, 2010 06:06

<< well iam guessing with all ???? after IPR I will not ask for anyones opion on here seem the cat dealer had no problem with finding the part when I told them I needed a IPR . Like I said in the last post hate free sites . there are a bunch of know it alls on here. Like I said in the passed Iam a A tech not some clown that just started doing this 25 years in the bizz . Just not up on the cat motors we see alot of jap and cummins stuff . not being a smart ass but thats the way it comes across deasrtboy trucks fixed charge a fair price guys happy thats all that matters in the end. Have a Good life will not post on here AGAIN thats for sure!!! >>

Don't feel too bad . I know there are CAT dealers out there that would have thrown a few parts at it too before getting it right. There are some Cat techs that just didn't get proper training or didn't learn the system. Sometimes the shop is tied up and puts the wrong guy on it.
I thought you did well without the proper equipment.

Edited: Tuesday July 13, 2010 at 06:11 by Mobiletech

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