I have a 1990 Gehl 6635 skidsteer. 2400 hours on the machine and I have owned it since 1200 hours. The engine has been very reliable, but it has recently developed a miss. Ironically, this is my second 6635 and the first one developed the same miss at the same hours. I never got that machine diagnosed as it burned. The miss first appears slightly above idle and will continue through the mid range. It will go away at full throttle or idle. It sounds like one cylinder is laying down and the machine will puff black smoke. The black smoke suggests to me the cylinder is getting fuel, but isn't burning it. I tend to think this is not an engine health issue. Here is a video of the issue. Notice that it comes and goes based on rpm: I started by cleaning the low pressure pump screen. The screen was totally blocked. I then changed the fuel filter. To help protect the screen, I added an automotive style in line filter before the low pressure pump. I found the pump was not drawing the air out of the filter so I elected to replace the pump. This work had no effect on the engine running condition. I then bought a cheap ($100 for a set of 4) replacement injectors and installed them. Not much of an effect on the engine running. I currently have the OE deutz injectors off to a shop for rebuild, but I'm doubtful this will help. Looking for thoughts on what to check next?
U kinda jumped the gun.. U probably shoulda simply swapped the injector out w 1 furthest away from the 1 that was missing.. By chance did u mark the one that was missing.?? THAT WAY, u can put it in a different hole when you get them back.. Good luck
Was it a filter specifically designed for diesel.? A lot of them are not and cause more problems than they solve.
How would I know which cylinder had a miss?
Get the engine in the rpm range where it’s missing the most and loosen the lines AT THE INJECTORS 1x1 until the engine doesn’t make any difference.. THATS your bad cylinder.. U loosen the nut AT THE INJECTORS and you’ll HEAR a definite miss.. tighten it back up and move to the next.. You’ll come across one that doesn’t make the engine miss.. that’s the bad one.. But, it could be a couple of different things besides an injector.. Could be valve adjustment.. Could be the pump isn’t putting the correct amount of fuel TO the injector.. Could be compression on that cylinder is low.. And about 2 or 3 others that I can’t think of..
tpg’s comments above lead to another question. Have you checked the valve adjustment.?
Deutz have a habit of bent pushrods too.
I'm currently $4,500 spent at my dealer and no closer to solving the problem. What we know is the issue will dance between cylinders, it can't be isolated to a single one. To me, this suggests that it's not an injector pump issue. The dealer was certain it was a timing belt problem. Because the belt was past due for replacement I authorized them to replace it. The dealer called to say that after testing, the problem seemed to have gone away. Well, I drove the machine 10' and it started missing. The dealer is now wondering if maybe it's the governor. Another $500 for parts and they have to pull the oil cooler back out. Parts so far: Cleaned lift pump screen (clogged) Replaced lift pump and filter Replaced return lines Added a pre-fuel filter Rebuilt injectors Compression test (450psi) Flushed fuel tank Replaced timing belt The engine starts well and runs at full throttle with good power. Midrange has a bad miss but going WFO or back to idle will clear the miss. Bouncing the machine seems to make the issue worse. When the tech tested it, he ran it in circles around the shop. When I tested it, I drove across the door threshold which had a slight bump. The moment I crossed the joint it started missing. With the timing belt having been replaced, the machine no longer smokes like what you see in the video above, but the miss is still there. Valves have not been lashed, but I don't hear a valve tick at idle and compression is good.
I take it u have the single cylinder separate pumps.?? Check the banjo bolts in each inlet.. The 2 front b/b should be wide open..& the last should be a pressurizing b/b.. it could be that the pressurizing bolt is weak.. and not holding enough fuel in the gallery.. I’ve also seen where the “overflow b/b” gets moved to where it’s not in the last pump anymore.. Good luck
Correct, there are 4 injector pumps. How does the restrictor bolt go bad? I could see dirt getting in it to reduce the flow, but in this instance we would need the flow to increase. The bolt has not been removed.
Are u gonna argue or pull the bolt.??
Perhaps, but you need to answer the question first.
There r 2 different overflow bolts. 1 is a restricted orifice & 1 is a spring loaded check ball and spring .. The orifice can/will get clogged and the spring can get weak and break.. If the spring is weak or broken, fuel will enter the gallery and right back out..
The dealer is reporting the bolts are all the same, no check. These are original and still have the paint on them.
Hmmm.. aslong as it’s at the dealer, did u ask them to look it up and see if it’s supposed to have an overflow valve.??
Hello from sweden! Did you find the problem? I think i have de same problem. Deutz 1011 engine ~6000h I have no orifice or check valve in the banjo, should not be when i lock in the catalog(all 4 banjo are same). Where is the orifice located on the picture i post nr.11? Any idea pumpguy? Thanks so far
It looks to me as it might be #11.. Is your lift pump working properly.??
Tanks for reply! Yes ofcorse nr11, but does the orifice sit in the fuelgallery or should it sit somwhere in the return hose? Does it have a part number? I will have a check at the lift pump, feels like it loose pressure when it stands over night. The engine runs a little bit rougt a few seconds when stands over night and Wont answer the throttle correctly. No black smoke. Filter is new.
Ur gonna hafta do some digging.. it might be a screw-in orifice that screws into the return line.. U might be able to unscrew it from the line and blow thru it. And as long as you have it disconnected, depending on if your supply pump is electric, u can turn the key on and check the response of the supply pump.. weather or not the fuel comes out immediately or if there’s a bunch of air, then fuel. (Have a bucket handy) If it’s a mechanical pump that runs off a cam, u can still check it but you’ll have to start the engine.. Good luck
Can't answer your question, but I had this happen to two machines and never figured it out. Replaced lift pump, blew out the line back to the tank, replaced return lines, replaced injectors, replaced timing belt, and replaced the injection pumps. The only thing that helped were the injection pumps, but they didn't eliminate the issue.
Will the unit run off of a jerry can hooked up to the fuel filters. Can be handy to prove whether fuel tank or lines is an issue.. Simon C
It actually sounds to me that she starving on fuel