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Bus Discussion => Bus Topics ( click here for quick start! ) => Topic started by: OneLapper on August 27, 2008, 06:22:38 PM

Title: Damaged 8V71 Injector?
Post by: OneLapper on August 27, 2008, 06:22:38 PM
I installed an air throttle a couple weeks ago.  This weekend I took my first trip with the air throttle and noticed that the engine had a very unusual surge in power when under load.  The engine would have good power for about 5 seconds after going to full throttle, but then the power would go away for 5 or so seconds, then come back and the cycle would continue.  The further I got the more the engine smoke under load (blowby tubes, not fuel smoke from exhaust) and the worse the power was.  I actually had to back down a hil about an 1/8 mile with a car trailer towed behind me.  Now the engine seems to miss at WOT under load, but again, in the weird 5 second cycle.

Did I damage the injector rack by not running the racks after installing the air throttle?  It never occured to me to run the rack.  I did that service about 3000 miles ago.

Thanks for any and all input.


Title: Re: Damaged 8V71 Injector?
Post by: NJT 5573 on August 27, 2008, 10:05:42 PM
 An air leak maybe. If you hadn't just worked on the throttle I would change the filters because thats about how they act when they plug.

 You can cold start it and feel each exhaust port for a cold one if you think its an injector. That will at least tell you what hole to look at. The way you have lost power but not prime, I wonder if the air is really opening the rack or is leaking off. Lost power, but still primed makes plugged filters a good bet too.
I have never lost a DD fuel pump but I assume when they are dead they quit.

When I change filters, I always dump them into a glass beer pitcher to see what comes out.

Make sure the manual shutdown valve is not flapping around and shutting the air off.

Title: Re: Damaged 8V71 Injector?
Post by: CraigC on August 27, 2008, 11:45:56 PM
I lost a fuel pump once the shaft at the seal area became worn. The system would bleed fuel down when shut down for a few hours. It would start rough not on all cylinders. It did not completely smooth out. Acted like some bad injectors. It did not leak fuel out of the seal so I thought. It did suck a lot of air in when running. My fuel pressure on the output side was 15 psi. lower then it should be at 1900 rpm's and fluctuated to 25 psi below normal. When checking the return fuel line the amount of air in the fuel was amazing. It looked more like foam. Using the cruise control surging was more noticable. I pulled some hair out before I found this one. Just one way a fuel pump or other air leak can act on the suction side of the fuel system.

Did you match wide open throttle position on the governor shaft to maximum air cylinder travel before tightening down the throttle arm. I center punch a mark on each for alignment purposes.  This way I know if they have slipped in the future or any time I take things apart for easy reassembly.

Running the rack has nothing to do with adding an air throttle. You have the governor between the two.

 Number 1.  I like NJT stated above would be looking at the stuff you worked on directly first. Some dishwashing soap and water in a Windex type spray bottle will find external leaks very quickly. Were your parts new or used. You would need to open the foot value to be able to check down stream from the foot value for leaks. Check the vent hole on the diaphragm at the throttle / governor to see if the diaphragm is leaking there.

 Number 2. It might not have anything to do with the new work. If you took on fuel just after fuel was delivered in a tank that was low it can stir up all kinds of stuff. If the station does not move a lot of fuel algae possibilities increase. Yesterday a friend started having fuel problems just a few miles after refueling.

Just a few wild ideas. Good luck and please post what it actually is for all of to learn from.

Just a couple of thoughts as sometimes this type of problem can be real frustrating.

Title: Re: Damaged 8V71 Injector?
Post by: OneLapper on August 28, 2008, 06:41:27 AM
Thanks for the replies.  I did change the fuel filters as soon as the I noticed the symptoms.  Both fitlers looked clean, I think there was only 2000 or 3000 miles on them. 

I have a pyrometer so I will try the cold start and check the individual exhaust ports/manifolds to see if I have a dead or dying cylinder.

I checked for air leaks to the cylinder on the governor plate.  I didn't notice any.  I had a friend push the throttle pedal down to the floor while I looked for a surging air cylinder.   It didn't surge.

How did you test or notice that the fuel pump was foaming the returned fuel?  did you disconnect the fuel line at the fuel filters?

CraigC,  unfortunately I did not index the governor shaft as I replace the entire plate that sits atop the governor.  The parts I installed were used.  The first thing I did was pull out of the garage and drive straight to the fuel station and put in 100 gallons, but again, I changed filters and it has the same issues.

Would a bad injector cause more smoking than usual?  Maybe this whole issue is coincidence.  The bus sat for four months in the garage without being started more than twice.  I'll keep you updated.  I'm going to mess with it this weekend.

Title: Re: Damaged 8V71 Injector?
Post by: niles500 on August 28, 2008, 12:58:07 PM
Sean (Odyssey) had a similar problem a while back - turned out to be a restriction in the fuel supply - FWIW

Title: Re: Damaged 8V71 Injector?
Post by: CraigC on August 28, 2008, 10:55:42 PM
I am not saying you have a fuel pump problem. I was only giving one example to NJT 5573's post for a bad fuel pump. I got my problem pump from another engine that I thought was running OK. I am sure this type of worn shaft problem did not happen over night. A leaky seal could suck air and leak diesel. Shine a flashlight to see if it is leaking fuel a drop every ? is acceptable. [ ? forgot exact time frame book says ]  I didn't know were my problem was other then in the fuel system. My symptoms were starting white grey smoke at start up and not firing on all cylinders. You could hear one by one start to fire. Going down the road it surged, much more noticeable with the on cruise control. I saw a small leak under the transmission this was running off of the bell housing. I thought that leak was trans. oil. After fixing the fuel pump I realized it was 100% diesel running from Front to rear of the engine along the value cover and running off the bellhousing.  If I had of used some dye in the fuel I would have found this immediately.  You do not have to dye all of the fuel. I would install my in and out fuel hoses to a 5 gals of  dyed fuel.The first thing I did was install a 100psi gauge to the secondary fuel filter. Running the engine at about 1900 plus the fuel pressure should be 55 to 60 psi hold steady but needle vibrating. At idle will fall 0 to about 20. I am recalling these numbers by memory but close enough to figure if you have a problem. In my case it would vary between 35 and 42 up and down. Next test was to connect a hose after the restricted fitting on the engine fuel return side. this fitting is usually on the engine with a number stamped in it. Not all the same size depends on the engine.  example R80  This fitting will return .8 gals per minute at 1200rpms. Next check fuel flow with this test. At the same time hold the line on the side of the container you are also checking for bubbles in the fuel system. This would be testing the entire suction side of the fuel system from the fuel pump to the tank. Mine looked like foam and the volume was short. Now, I have problem were is it???? I am not saying this is right but this is what I did next. I added 20 psi. of air where the pressure gauge was installed on the secondary filter. It took a couple of minutes but fuel started to gush out and then only air came out of the fuel pump. At first I wondered if I had pushed the seal out. I removed the pump and did a visual inspection still not seeing the problem. I already knew the pump had to be replaced. Once taken apart  you could see the worn shaft.  I have also used pressured air regulated to a low pressure to look for suction leaks else where on the engine before the fuel pump.

After the above test a friend install a permanent digital fuel pressure gauge and new filters.  Reciently about three miles after taking on fuel he lost rpm's. If he would let up on the throttle the fuel pressure would rise. Try the accelerator again and it would slow down & loss fuel pressure. This happened with several tries. He was only a few miles from home so he nursed it along.  The fuel came from a low volume fuel supplier. We wonder if it was just after a fuel delivery to a low tank that stirred up the junk on the bottom of the tank. Bottom line plugged fuel filters. These new filters had 400 miles since new and 2 topping off with fuel of about 60 gals. each. He is installing a Racor fuel filter as I write this. One you can visually see if you have fuel filter problems. This is a alternative to guessin g you have fuel filter problems with the stock type.

You can use a very large screwdriver to hold down the top of each injector to see if that cylinder is firing or not. This is so the injector rocker arm will not operate that injector [ push down that injector ]. There will be no doubt if you have a misfiring injector. I have seen some use a heel bar for this. If you have Jake's be careful and do not lever under the Jake to hold down the injector and ruin the thin sheet metal piece under the Jake.
Gives you some more places to look. 

Title: UPDATE: Re: Damaged 8V71 Injector?
Post by: OneLapper on August 31, 2008, 12:30:30 PM
Okay, I removed the fuel return line to the tank at the bulkhead fitting.  Started the engine, ran it for a few seconds, brought the idle about 1200 rpm.  When the engine started to miss, the fuel would stop flowing!  It would return to a trickle, foaming and spitting, then run clear again.  The engine would smooth out when the fuel ran clear.  When I ran the engine near 2000 rpm, the engine would stumble hard, and again the fuel return would start to trickle out.  The engine nearly stalled.

Is this a fuel pump going bad?  More later, off to a picnic!


Title: Re: Damaged 8V71 Injector?
Post by: makemineatwostroke on August 31, 2008, 12:39:27 PM
Onelapper: that problem is in you fuel pickup from the tank could be a air leak or the tank they have a screen on the pickup tube in the tank

Title: Re: Damaged 8V71 Injector?
Post by: DrivingMissLazy on August 31, 2008, 12:42:00 PM
Onelapper: that problem is a leak in you fuel pickup from the tank

Or at least somewhere in between the fuel pickup and the fuel pump.


Title: Re: Damaged 8V71 Injector?
Post by: van on August 31, 2008, 04:24:01 PM

   Could be any one of the above,but I would check the easiest things first.I've been through all this before checking for blocked P/U in the tank,maybe a leaking P/U line suckin air,cracked primary filter housing ,filter gasket not seating properly to the filter housing ,lines to the pump .Did have to change the pump however drive shaft was sheared in half (rare occurance So I'm told) still had a fuel delivery issue ,then checked the return lines ,check valves .Every time i would pull the filters they had fuel (3/4 full)but not full.finally pulled the main supply line (to the primary) and found the line was collapsed,it would deliver just enough fuel to start but not much else,check the inexspensive stuff first ,before spendin alot of uneccissary dough and goin through alot of grief for nothing

  good luck and update the post with your findings


Title: Re: Damaged 8V71 Injector?
Post by: OneLapper on August 31, 2008, 06:13:47 PM
Okay, I feel as if I'm getting closer to figuring this one out.  It must be coincidental that I installed the air throttle and this problem started.  The bus sat in my garage for 4 months while I installed the power steering and stripped the right side of the interior to remove the moldy, mildew, nasty rotting fiberboard and insulation (not to mention 40 years of crap stuffed down the heating vents, oh what treasures)!

The only possible indication that something may have been wrong was that the bus was low on power coming back from South Carolina, but when the throttle pedal froze, after the muffler popped off, I thought I fixed the low power problem by cleaning up the melted rubber boot on the throttle cable next to the muffler.  The bus had tons of power after that fix and it ran GREAT from NJ to Connecticut, about 100 miles.

In the morning I'll hook a fuel jug to the supply line and restart the engine again.  I'll see what happens.  What I find difficult to understand is the cycling of clear fuel and foamy (or no fuel at all) in five to ten seconds intervals.  That just doesn't make any sense.  If it has the same symptoms, then it must be the fuel pump.  If it doesn't, I'll test the line from the tank to the fuel filter.

Thanks for the replies.  It's helpful to have you guys throwing out ideas to check.



Title: Re: Damaged 8V71 Injector?
Post by: CraigC on August 31, 2008, 08:20:26 PM
Do you have a Detroit Diesel V71 Service Manual?  If so look in section 2 Fuel System. Look under 2.0 Shop Notes- Troubleshooting-Spec-Tools      Mine is a 10-1989 edition
pg 11 "location air leaks in fuel system" , "pressurize fuel system-check for leaks",
pg.12 "detecting internal fuel leaks"

 If you do not have a manual get one, they are on e-bay fairly cheap. The  amount of info. in them is almost their wt. in gold
If not I will scan, fax or mail those 2 pages to you.

Just make sure when you ran the test  you broke the fuel line after  the R80 or ? number  restrictor fitting on the engine. This is very important. If you bypassed this fitting you need to rerun the test. All of results you just gave can happen if you broke the line in the wrong place. Just double checking.

If you have to replace the fuel your profile says you have a 4106. Make sure that you get a Left Hand turn pump.
5199560 is the correct pump. It will have "LH" stamped just above the larger fuel port. The by relieve value cap will also be on that, or right side. There will be about 1/4 circle with a arrow pointing counter clockwise. Make sure  everything is exactly like your current one.

There is a fairly small coupling between the fuel pump and the engine that can not be seen until you remove the pump. On my 8V71 I would have to pull a main water pipe and dump the coolant to get to the bolt toward the firewall. I use a wrench I have bent in a semi circle and cut the other end off. A bite of pain but better then dropping the coolant for one bolt.  Last week there were 2 on e-bay to give you an idea want one look like if needed.

I would check tank pickup first. That is if thare is junk there you will not blow it back int eh tank to haunt you later. Next, I would  add pressured air about 60 at the secondary fuel filter. Look for leaking fuel and or air  large leaks will occur immediately and small ones will take several minutes. The book says 20 to 30 minutes. Soapy water [ dishwashing soap in a windex type bottle ] to look for an air leak if you do not hear it. Open fuel tank lid and listen for bubbles. That would mean that the check value by the primary filter is leaking. A lot of the older GM's the fuel lines rot out from the tank to engine bulkhead. Maybe disconnect fuel line at the check value on the bus side as another check and only isolate engine as a check from the bus fuel. You will need to cap off the fuel return line.
I use a small electric fuel pump in a gal can of diesel and pump fuel to purge enough air out of the system for the engine to start immediately. That is if you blow all of the fuel out of the engine from a leak. Not a 100% by the book just the way I would do it. Air will pass through a hole or connection where diesel will not go.

Lotsa luck on the search.

Title: Re: Damaged 8V71 Injector?
Post by: OneLapper on September 01, 2008, 07:13:14 PM
Craig C,  you've been very helpful.  Thank you.  I got a chance to spend a few hours to poke around.  I pulled the secondary filter to see how much fuel was in it.  It was full but I did find that the rubber oring was damaged.  I installed a new one.  I checked the Primary filter and that one was 3/4 full with fuel.  I'm not sure why.  I noticed that the fiber seal washer was missing from the bolt that holds the canister to the filter housing.  Again, I installed a new one.  I topped off both filters by removing the plugs on the housings and topping them off with clean diesel.  After this, I started the engine and let it come up to 180 degrees, ran it up to 2100 rpm and let it sit there for a minute or so.  The engine smoothed out considerably. 

I then pulled the return line at the same place as yesterday and checked the fuel flow.  It appeared to be much clearer, but there where times when it would get foamy and the engine would stumble.  I bolted everything back together and decided to go for a spin.  She ran MUCH better, but it still has a problem.  The power would be spot on one minute, and then it would be noticeably lower.  I could feel the  power difference but more importantly I can feel the engine missing on more than one cylinder.

I'll have to take the chance at get it 80 miles to my garage later this week.  I have to tow a 2000 pound trailer, but that shouldn't be too bad.  She wouldn't pull my 7500 pound car trailer up a hill which is why I'm looking into this problem.

More later in the week.



Title: Re: Damaged 8V71 Injector?
Post by: OneLapper on September 23, 2008, 06:34:06 PM
Update:  I got her to my garage.  Drove 80 miles with an empty landscape trailer, and except for getting on the highway without any head start, I didn't piss too many people off.  It really didn't run well and it was extremely low on power.  It was easily 20 mph slower on a couple of hills.

I picked up a used, but rebuilt, fuel pump for $0 (how often does that happen?) and pulled out the old pump.  When I took it apart I found the pump drive shaft was shot.  The seals and the shaft showed considerable wear so I'm assuming that the pump must have started sucking in air.  The shaft has slight grooves from the seals.  The seals are rock hard, too.  There is no flexibility left in them at all.  I also noticed that the way the seals were install facing the same direction which means the last time the pump was rebuilt was before they recommended installing the seals facing each other (late 80's?).

The replacement pump has nice and shiny new seals and shaft.  I'll install it tomorrow.  I'll also install a small electric fuel pump I took off an old diesel crawler I'm restoring.  That should work well to prime the system and give me the ability to use a small fuel jug if needed.

Title: Re: Damaged 8V71 Injector?
Post by: CraigC on September 24, 2008, 02:19:34 AM

I temporary hook my elec. fuel pump to a plug in the secondary filter. After words install a fuel pressure gauge in the same port, at 1800 rpm's you should have 45 to 70 psi needle will vibrate. The needle will vibrate about 4 psi in both ways off center. At idle it will fall to 20 to 0 psi. If you had of installed a pressure gauge before the fuel pump change it would have had large flucations to match engines erratic behavior. I would double check the return line for air bubbles. Check for fuel return volume at the same time. The return return should be 0.8 gal. per minute at 1200 rpm's.  This is after the restrictor fitting R80
I hope you have found all of your problems. If so it should run like a scalded dog--  greyhound!!!

Craig C

Title: Re: Damaged 8V71 Injector?
Post by: OneLapper on September 24, 2008, 07:29:55 PM
CraigC, the current engine should run much better with the new fuel pump, but it still has a "dead" cylinder.  One cylinder has very little compression and the amount of blowby is bad, even embarrassing.  When passing through New York I got honked at, and one lady honked and flipped me off!  Most people wouldn't care, but I do my best to be responsible to the environment and community, and that's tough enough with the lousy emissions these two strokes' have.  Combine that with the amount of unburnt fuel bypassing the rings!  Yikes!   I also have a leaking tranny output shaft seal that makes a mess all over the back of the bus when I'm driving.  That doesn't help the way things look, either!  LOL!

I commute 160 miles per day.  I use a diesel Jetta that gets 46 mpg or my bmw motorcycle that gets 44 mpg.  I have a Dodge 3500 diesel that gets 17 mpg and it kills me when I have to drive it!  I love that truck, though.  Of all my vehicles, it's had the least problems by far.  It also has over 100k miles on it.

Title: Re: Damaged 8V71 Injector?
Post by: OneLapper on October 09, 2008, 07:02:13 PM
For those interested, the new fuel pump FIXED the crappy running 8V71.  I finally got to installing the pump tonight, and after repriming the fuel system, she fired up and the engine surging, gurgling, burping, etc, all but completely went away.  The 200 mile road trip will have to wait till next weekend, but it was easy to tell the engine was running much more smoothly.

Now, it still has cylinder with a broken piston ring, but that's another matter.

Title: Re: Damaged 8V71 Injector?
Post by: Barn Owl on October 09, 2008, 09:53:51 PM
Thanks for the update. This post will make a good reference for someone one day.