Troubleshooting a miss

[FMJ]

Guys,

I have a truck that starts and runs ok, but has a slight miss. The #1 cylinder appears to be the culprit, checked exhaust manifold with IR thermometer. During my investigation I felt all the injector lines coming from the IP, #1 feels like someone is tapping on it with a hammer at the rate that the cylinder would fire at idle. The other 5 IP lines do not have a knock feeling at all. The IP appears to have been recently replaced as some of the return hoses from the IP are not secured to the block as they should be, and some of the steel lines have been bent slightly. Is it possible that the injector, or the injector line for the number one cylinder was damaged during the swap creating a blockage and subsequently the knock felt in the IP line?

Ed

 

[rockman]

Does the #1 fuel line flow well?

 

[Screamin' Metal]

Its probably the Injector....though you can troubleshoot it by starting the motor, letting it idle, then loosen off on the infector line.....not alot but a little.....you should have diesel seeping out. If not, backtrack the Injector line to the IP, loosen the line there......if no leakage....they is either a blockage at the pump. If it leaks at the pump but not the injector....Its probably the line. If its leaking at the injector.....its probably the injector.

If at the injector your getting fuel.....pull that injector and see if it pops at the specified PSI. Injectors are designed to 'pop' when the pressure is achieved.....if not, that could be your miss.........

 

[Screamin' Metal]

If its making a really loud rattling sound when the IP is at that dead cylinders line....I'd say something is messing up in the IP....which won't be a cheap fix. You should tell pretty quick with checking the line.....also make sure there are not any 'pinch marks' anywhere on the injector line......

After all is said and done and you do get her running agian correctly....put a good Stanadyne diesel fuel filter on just before the mechanical fuel pump.....crap getting into your fuel is the worst enemy of these trucks.........

 

[FMJ]

There is no audible knock, just the feeling in the number 1 steel line. I've got extra injectors, and lines. We'll see what happens today.

 

[G-Force]

Crack the line at the injector while running at idle. If there is a change in idle then chances are that cylinder isn't the problem. If there is not a change then swap out the injector with a known good one from another cylinder. See if it follows the injector or stays with that cylinder. If it stays at the cylinder then its probably a compression problem with the cylinder.

 

[usmarines72]

how's your exhaust? Does it smell like diesel? Standing on the passenger fender, does it vibrate pretty good?

 

[Screamin' Metal]

FMJ, oh sir....hows the Motor+ Changed out the line and injector?

 

[charlietango]

I am having a similar problem but mine has an audible knock.
(sorry to thread jack I can start another one if need be)

Picked up my A2 2 years ago and it had an audible tick or knock that my M109A3 didnt have. Changed the oil and filters, fuel and filters. still there. So I just drove it that way. figured something obvious would pop up soon if it was serious. This past fall an injector line broke while driving. cracked clean right at the IP flange. So I ordered a complete set from Memphis figuring they must all be ready to go and hoping maybe that tick was another broken line I didnt notice yet. Also since summer I also had a fuel leak at or near the IP that I could not find. So I replaced all the lines one day, bled them to make sure all the air was out, tightened them down and .... still ticking. I noticed that the lines themselves, if I grabbed them, hammered with the sound of the knock. So I changed out number 6 with one from the 109A3(see below) and it felt smooth! Fed up but confident it was now the injectors 'tapping' as I found on google I took it to a reputable Diesel/Turbo shop ( Western Turbo, Diesel & Fuel Injection ) and they DL the manual, set the lifters to spec and fixed a plug on the IP which was the source of the fuel leak, checked the injectors. Phoned me 4 hours in ($98/hour) and said that they are baffled as to what the problem could be. Said there is a SLIGHT exhaust leak but was 95% sure that was not the source of the knock/tick/miss. he left me with 3 options.

1. take it home now and pay us the 4 hours.
2. charge up another ~4 hours to change the exhaust man. gasket which probably wont fix it.
3. charge up anywhere from 6-15 hours to start digging into an engine that was built in 1985 and try to not find a problem.

so I took it home disappointed.
what the **** is wrong with this engine? should I just re-assemble the engine I have (below) and brave the job of engine swapping or is this shop out to lunch with their injector diagnosis (based on feel 1-5 hammer and the #6 I changed is smooth)
I am really at a loss and I dont want to waste money chasing ghosts.

I have since sold the m109a3 and retrieved most of the mechanical parts from it. THe guy dis-assembled the IP, compressor, water pump etc from the engine block and I ended up buying it that way. This engine ran REAL smooth before he started the 'bob' project and has a rebuild tag of 1999 on it.

 

[FMJ]

FMJ, oh sir....hows the Motor+ Changed out the line and injector?

Swapped out injector, line, changed filters, tweeked droop screw. . .

Still has a bit of miss at cold idle, but after it's been running 10 min or so it's gone. . .
Starts much easier now that I turned the droop in a bit, so all in all, I think it'll be fine. Truck looks to have sat for awhile in the NG yard up at Santa Fe, and I've only put about 150 miles on it since I brought it home, still some old diesel in the tank, but I have added about 10 gal fresh, plus power service cetane booster with cleaner, few more miles on her and I'm thinking it'll be gone completely.

Ed

 

[jonesal]

For the uninformed, can you expand on what the droop screw is and what it does? I missed that one in the TM.

Thanks,
jonesal
'70 M35A2

 

[FMJ]

Controls fuel delivery up to 1600 rpm.

 

[Screamin' Metal]

Swapped out injector, line, changed filters, tweeked droop screw. . .

Still has a bit of miss at cold idle, but after it's been running 10 min or so it's gone. . .
Starts much easier now that I turned the droop in a bit, so all in all, I think it'll be fine. Truck looks to have sat for awhile in the NG yard up at Santa Fe, and I've only put about 150 miles on it since I brought it home, still some old diesel in the tank, but I have added about 10 gal fresh, plus power service cetane booster with cleaner, few more miles on her and I'm thinking it'll be gone completely.

Ed

Yes sir....she should straighten out some more after she's run some.....I was a Chief Petty Officer on loan to the Marines to fix and modify stuff for various things....you know the drill.....anyway....the motorpool can be hard on these trucks just being set up for awhile till they decommisson them......

 

[charlietango]

the troubleshoot manual leads me into the block on most of this. that worries me.

do I smell a rebuild? or is it best to find a replacement?

I will try to record the noise and post it up

 

[FMJ]

the troubleshoot manual leads me into the block on most of this. that worries me.

do I smell a rebuild? or is it best to find a replacement?

I will try to record the noise and post it up

Easier, and faster to swap motors, but there's always a question mark associated with the "new" motor