Sunday, September 02, 2007

Diesel Engine Repairing Troubleshooting


Diesel Engine Repairing & Troubleshooting requires some common sense and basic fundamentals to find a problem whatever it may be. I have lots of experience in the "will not run" category, there is one thing you should do first, "always check the source!"

Think about the source everytime you begin your search for a diesel engine fault. On a basic diesel engine without electronics the first thing you do for a "no run" condition is check the fuel tank, is there fuel? Check the fuel filter for the amount of fuel remaining in it, it should be high enough to reach the filter base pick-up [where it screws onto]

If you've got fuel just move up the line to the Primary fuel filter and then to the Secondary filter, the Primary filter is on the vacuum side of the fuel transfer pump while the Secondary filter is on the pressure side of the transfer pump. If your fuel filters are primed and unrestricted crack a line on the pressure side of the fuel transfer pump and crank over the engine, check for a positive fuel flow [if not checkout the pump which typically is a mechanical pump that runs off the camshaft] in the case of the 3116 Cat the pump is in the Governor housing.

If you have fuel go to the injection pump and crack a line and check for a positive fuel flow while cranking. If not check the fuel shutdown solenoid for proper operation [could be a mechanical or electrically activated type solenoid] then the injection pump drive, usually off of the camshaft gear. Once you understand that a diesel engine needs air and fuel to run that's where you start and always at the source. This a general procedure that might save you some grief and a tow truck bill.

Another favorite saying in this industry is "always check the simple things first!" It isn't rocket science but once you start going down the wrong path it will cost you time and money...

41 comments :

Anonymous said...

Nice blog. I would like some advice from you. We have a 1990 Thomas MVP with the 8.1 Detroit Diesel used for our religious organization. We have a problem that you may have heard of or have experience with, with the cooling system. I don't think it was designed very well. There are hoses of several different diameters and pressures. We replaced all the hoses but there is a leak coming from a small caliber hose which is difficult to access, as we have to remove other hoses to get to that one. Maybe if you have time I can take a picture of this and send it to you. We tried everything to keep it from leaking, even putting high-temp silicone around the edges and clamping it super tight, but it still leaks bad. And the funny thing is sometimes it won't leak at all. We have had to drive the bus with water jugs and keep stopping and filling which is very tedious. Other than that the bus runs well but it sometimes has difficulty with the power steering. Where is that reservoir located on this bus, in the front by the steering gearbox? Finally, the gauges work and stop working intermittently. Is this a hard problem to fix?

Any advice is greatly appreciated. Maybe you can even start a bus repair forum, as I don't see one on the web yet...

John Whelan said...

Concerning the leaking hose, have you pressure tested the cooling system. A rad shop or any repair shop will have the tool, the hose can be checked over while under pressure or it could be something else?

Your power steering reservoir on an MVP should be in the engine compartment on the right side. Follow the largest hose[inlet hose] from the PS pump this will lead you to the reservoir.

The guages run off fused ignition power, check the feed wire to the panel, there may be an excessive draw. Some circuits have fuses that reset automatically when they cool down, check for a weak fuse or too many circuits on one fuse?
John

towjoe said...

hi john I really need some straight talk cause my cat dealer is blowing smoke you know where..1990 gmc topkick 3116 alison auto ect.483,000 remaned from crank up approx 7 years ago. aug 7 begain to show signs of injector fouling out. go to dealer, spring on #5 broke, bent rod also as a result.they said in order to do it right i needed to get all 6 injectors reman.sept 24, again injector fouls out bad I need a tow to get back to dealer,its been there over a week now,they have spent two days troubleshooting "a fouling injector" result I need to replace fuel transfer pump assembly cause all of a sudden theres no pressure to troubleshoot engin.???today is the 2nd oct. find injector not seating properly, i get call from dealer #1 sleeve bad gonna have to replace all 6!!! What did they do to my truck???and Im gonna refuse to pay for all this since all along it was just a fouling injector. Help SOS please Im gonna need an ace up my sleeve or an act of god to help me thru this..

John Whelan said...

All the failures you have mentioned [except the broken spring on the #5 injector]are a nagging problem with this engine. For some reason #5 cylinder have problems with exhaust valves, they don't want to stay in one piece so I would investigate that. The injector seats are a common problem as well, since compression can sneak by and get into the fuel system causing a very poor running condition[air in fuel].Replacing or machining the injector seats are required to fix the problem. Generally the top end on the 3116 namely the head is the weakest component.
John.

Anonymous said...

1990 300D 2.5 Turbo mercedes sedan lost power and rpm about 1 week ago with grey smoke bellowing out the rear.
Barely made it back home and had it
towed to garage for repair. It
would be OK and then not be OK for
mechanic until finally he ordered &
installed a vac. solenoid.
the car ran OK for 2 days. We drove it 200 miles on a short trip when the same exact problem occurred and it was sitting in the hotel lot until the mechanic who had repaired it at home sent a tow truck the 200 miles to tow it back to him. Now the mechanic tells us it's driving OK.
I need MY car and don't know what
to expect to happen or how he's to
research this problem which is what
he tells us he's doing. I'm
wondering if the solenoid was the
problem since he said most people
he talked to said "they hardly
ever go out." The car has about
182,000 miles.
any thoughts about
how we handle this problem.
sastephens@ualr.edu

John Whelan said...

If the vacuum solenoid is controlling fuel demand on your injection pump then I can understand why this problem is intermittent. Changes with engine load and fuel demand requires fuel injection timing to be controlled somehow. If the vacuum solenoid's job is to read what load level the engine is at and fails you will get excessive smoke because the engine is not burning it off and receiving too much diesel.
There might be a deeper problem past the vacuum solenoid.

Anonymous said...

Hi John- I have an '89 Sportscoach motorhome with a 225 hp 3208T Cat with Allison trans.in a Spartan Chassis. The radiator is clear up front in the bow with hardlines and hoses running 35 feet to the stern. My question is- how do you drain the cooling system completely, and more importantly, get all the air out when refilling? It has an accumulating tank with the cap on it and a sight glass as the highest point in the system. I haven't seen a bleed port on top of the radiator. My old water cooled Volkswagen Vanagon required jacking up the front and bleeding air out through a vent on top the radiator. Any help would be greatly appreciated. Thanks, Phil

John Whelan said...

Draining coolant from the lowest point will do the job along with a 5-10 pound boost with air pressure if available.
The best way I've found to bleed air from the system is to crack a line on the return side of the cooling system while the engine is running.

Anonymous said...

hi john,
I have a ASV skidsteer with a four cylinder cat engine. Recently I filled it at the pump at a local gas station and come to find after that out of 30 gallons I got about 10 gallons water. now this issue has lead to a chain reaction of other problems. I finally got all the water out of the system but the engine cranks very hard. I removed the battery and load tested it, and it tested good. I then took out the starter and brought it to a rebuild shop and it ran fine and they didn't suspect any problems I then put the starter back in making sure all the connections were clean and still cranking hard. it cranks way to slow to start a diesel engine or any engine for that matter. Would you have any suggestions on where else to look for a problem?

John Whelan said...

Water in the tank is deadly in a diesel fuel injection system. The main reason is the lack of lubrication which has probably damaged or seriously shortened your injection system life.
You may have poor injection combined with the high compression causing hard starting. Over fueling [will cause excessive fuel knock].
I would pull an injector and get it checked out for scoring damage.

Anonymous said...

hello we have a 5.9 cummins engine that has exsessive blow by and blowing oil out of the tube we think its time for a ring job what do you think?

John Whelan said...

You have a major blow-by problem and rings will help but check the cylinder bore wear and the cyl. head wear as well. [Depending what you have planned for this vehicle] if you want to run it for awhile I would go right through everything including checking bearings crank and camshaft which almost spells a rebuild.

bob said...

John; I have a 3126 cat that developed a coolant leak into the oil. The valve cover had accumulated a thick goo along with the cover breather filter. I cleaned them up and thought I mite have a leaking injector seal. Dropped the oil pan to clean it up and investigate a little further and it was fairly clean - no parts or pieces.The oil I drained was extreamly thick. I have cleaned up the top and bottom end with degreaser and put in some coolant to possibly pressurize and find the source of my leak. Coolant drained out the front of the crankcase at a good rate. The 3126 has a belt driven water pump so I didn't think my leak was there. Even with the thick oil the engine ran and I didn't have any issues that I knew until the driver reported a whistle which I figured for an air leak in the air cooler system. I don't know the front end areas where coolant could develop a leak of this magnitude and still run so well. My next step was to look at the oil cooler however it runs at a higher pressure than the coolant. Hopefully you can send me in the right direction. Thank You Bob

John Whelan said...

Bob,
Normally an oil cooler failure creates oil in the coolant. If it's leaking like most of these models do it may be worth it to reseal it and do a visual on the cooler bundle.

The block is a dry sleeve [integrally cast cylinders] so other than a head gasket or block problem I can't think of anything else.

The one test you could try first is pressure test the cooling system. Remove the oil pan, have someone turn over the engine by hand & observe. You could up the pressure above normal, 15 psi or better.


Please comment again on your findings...

Rick_&_Karen said...

Hi John. Have a two cyl marine generator slow turning 1800 RPM Lost power ..checked to find it only running on 1 cyl. Fuel is showinbg up in the oil pump and exhaust. Susepect connector between engine and mech fuel pump or piston rings . We're tied to a dock in Newfoundland trying to troubleshoot before we take it apart...simple first. Thank you. Rick www.wanderbirdcruises.com

John Whelan said...

I would pull the injector first and check it out. If it's over fueling badly you'll get excessive fuel in the crankcase and out the exhaust[lots of white smoke].

Jeff said...

I'm Jeff and have been a diesel mechanic for around 25 years, but I don't have much 3116 experience. We have a 1996 topkick towtruck that hasn't ran in 5 years. We got running with very little problem and it seemed to run well, I repaired the hydro valves and as we were bleeding the air out of that system the truck died -- like it ran out of fuel, check the fuel and added 15 gallons, we could not get it to run again at first without ether -- got it running but only at full fuel wouldn't idle and when it died it wouldn't start again blead all the lines changed filters, all the obvious stuff including running a fuel line straight from the tank to the pump.
Well the boss decided to put a pump on it, after all the bleeding of air and a lot of cranking still the same problem, ran at full fuel but no idle and no restart, I think and thought all along it would be injector issue, I could use some advice and help and very appreciated.
freedinwy@hotmail.com
Thanks
Jeff

John Whelan said...

I would check the fuel rack during cranking. The governor uses oil pressure to move it slightly to get the engine going. If you have to physically use the throttle to start then the rack is sticking. If you're doing this and it still doesn't start or idle you might be losing your prime. I know you ran a line direct but any fuel lines that you did not eliminate during that step give them a close check. The steel lines are famous for rubbing through.
If it runs OK at full throttle then these points should be checked first. You can also hook up a clear line to the fuel return line and check for air that way.
Also, make sure you're not losing compression into the fuel system past the injectors. This causes a pressure build up in the fuel tank.

Anonymous said...

Hello, I have a 1990 GMC7000 Topkick with a Cat engine, I believe a 3126. The truck was running when parked 5 to 6 months ago. We live in Oklahoma and had a mild winter, I didn't do any engine winterizing at all. We tried to start the truck and it cranks fine but doesn't even try to fire. In the past it would start extremely easily even when cold. I have very limited to no experience with big truck engines so we looked at what I believe is the fuel water seperater on the pass. side with the clear cover. It was full as always. I pulled the filter after the seperater and it was full. We emptied it and cranked the engine for about a min. or two. pulled the filter again and it had not filled up. I emptied the seperater to about 1 inch of fuel left in it and cranked the engine for a period of time and it didn't fill at all. Searched for the fuel pump and found lines going to the pass. side tank. Is there a pump in the drivers side also? I need the truck in two days and I have no idea what to do next and I don't want to just throw money at this. Please help A.S.A.P. Thanks, kmac.

John Whelan said...

Fill your fuel filters with clean fuel and find the priming pump on driver's side of the engine. It is an upright cylindrical shaped housing with a round knob that has to be turned out counter clockwise until it's free, then pumped in and out to build up fuel pressure which is in fact bleeding the system. It's been sitting for a long time so you might have to crack a line between the tank and the first filter and use pressurized air forced into the tank filler neck (seal with a shop rag)to push fuel through the lines.

Anonymous said...

Hi John.

I have a 98 GMC 8500 with a cat 3116. Over the last two weeks we have been having electrical problems with it. yesterday morning it started and it ran fine all day. turned it on and off a couple of times and no problems. I went to start it again this morning and when i turned the ignition on the backlights on the dash were flashing and the signal lihts would turn on sparatically. Checked all of the fuses and wiring harnesses and all seems fine. Any help would be appreciated. Thanks Peter

John Whelan said...

Sounds like a bad ground in your dash. If a light has a bad ground it will find the next best ground which is usually through another light circuit. This causes the new ground host to operate as well.

sean said...

I have recenty bought a mixer truck with a cat 3126 , the oil light came I have done a manual pressure test and is low. i put new oil put new filters ,still low. There is smoke coming out of crankcase breather please help.

John Whelan said...

I would check out oil filter(cut it open) for metal particles or take an oil sample and get it analyzed. If you have lots of blowby the engine might be getting tired. The next step is pull the oil pan and check out the oil pump and main brgs. for wear. I've changed oil pumps on the 3116 for low oil pressure but none on the 3126. Just take one step at a time.Good Luck

Nicolebh said...

Hi John,

What a great service you are providing. We recently purchased a 1998 GMC Savana 3500 mini school bus and have not had very good luck with it. I have only been able to drive it twice, both times from the garage it was safety'd in and both times it ran just fine until I got it back to my parking lot. Then it wouldn't start. We had to tow it back and bleeding the lines got it started again. It sat for 10 days because we were waiting to get it painted. Whem we went to start it again, it wouldn't. Do you have to start this vehicles daily in order to make sure they are working? Also Is there such a thing as an overall diagnostic test for school buses to determine what is working and what isn't like they have for cars? I would just like to know once and for all if there is a way to make this reliable and fix it all at once otherwise the towing costs alone are going to get formidable?

Thanks for your help,
Catherine in Canada

John Whelan said...

I would consider checking the fuel pump. It's in the tank and is a common GM problem. One thing you can try is remove the fuel cap and listen while someone turns on the ignition key.

You will hear a short 3 second buzz come from the tank which is the fuel pump priming the fuel system. (if it's working properly)

Another tactic is get someone underneath the fuel tank banging on the bottom (while a second person is cranking over the engine) which sometimes jars the fuel enough to start the engine but by this time the pump is ready for a replacement.

This method works sometimes and is handy if you are stuck and just want to get it to a garage without the possibility of a tow job.

Jim Bisel said...

interested in the special tools needed to do tune up work on the 3116. I am unsure exactly which tools they are. can you help?

J. E. Whelan said...

Jim,
search this blog for cat 3116 / cat 3116 tools and all my posts will show up, I have a page with tool numbers on it. Also contact a cat dealer for a price.

Anonymous said...

I would like to figure out which Inj is causing a mis under load on my 3116. How would I determine which Inj is missing?

J. E. Whelan said...

Remove the valve cover and feel in behind with your finger. The fuel rack pin can be moved in and out while the engine is running to activate an over fueling condition on each injector which will help you determine if there is a miss.

Rick said...

Hello,
We have a 1999 Thomas school bus with the cummings engine 2 weeks ago it died on a route. No codes, my boss had me replace the lift pump, injector pump, all filters and had the injectors checked everything seem fine. The problem is it starts and surges for about 10 seconds and then dies. It will always start again but it keeps doing this. Any other thoughts would be helpful. And we do have good fuel pressure

Anonymous said...

i have gmc topkick deisel engine starting fine but now the starter will not turn over at all starter has been tested and is good what do i check for now

John Whelan said...

Rick,
We have replaced the CAPS pump on a few of our Cummins ISCs (if that's the model you have?) there is usually no codes and the engine does not run. Unfortunately it's not a cheap fix but necessary. Your "no run" symptom matches one we had recently.

John Whelan said...

anonymous,
If your starter is fine check power to the solenoid from the key switch in "start mode". You can also jump battery to the switch terminal on the starter solenoid. This bypasses the wiring and key switch power.

Anonymous said...

I have a 99 gmc topkick with a 3126 that is running like shit. You push the throttle and it falls flat on its face then takes off. This is my tow truck please any ideas would be greatly welcomed.

John Whelan said...

Codes? The engine ecu reads the throttle position. It's hard to say without Cat software to see what's going on. Fuel filters first before anything else.

Unknown said...

We are having some issues with our buses surging. They have cat 3116 engines. We have adjusted the valves, changed fuel governors, replaced fuel filters and the problem still exists. I beginning to think the problem might be with the fuel rack itself. What do you think?

Unknown said...
This comment has been removed by a blog administrator.
John Whelan said...

The surging on your 3116 Cat could be air in the fuel. What I do is get a clean pail of diesel and bypass the first fuel filter and fuel lines from the fuel tank. Run the engine and load it up to see if there are any changes. The fuel rack just moves the injectors by way of the governor mechanically so that would not cause a surge.

Anonymous said...

Howdy John! I love your blog, and have found lots of good info in your archives that has saved the day. We have a 2000 Thomas MVP-ER with a 3126B/MD3060. I'm getting enough fuel in my crankcase that oil is spitting out of the breather tube in a big way. I've looked at the service manual diagram depicting the transfer pump, and it seems to be attached to the HPOP. I can't tell by the diagram, is the fuel transfer pump oil cooled, or operated? Could I be somehow getting fuel into my oil supply through the transfer pump? I've heard this could also be injector seals, but I thought that would cause the mark on my dipstick to go down, and not up. I don't have a hard time starting it, and it seems to run fine, but I want to determine why there is fuel in my oil before my turbo seals and bearings become unhappy with the situation.

John Whelan said...

I would definitely do the injector seals first which is a very common problem. A bad seal will cause fuel dilution in the oil with a level increase.