Sounds like a misfire please help!

[Domterry12]

Ok here’s the story. I’ve read through countless threads on here and some touch somewhat on the subject and give me insight on things to try but I haven’t seen my problem or a resolution so I’m gonna ask myself!

so I bought the truck a couple months ago.84 m1009. My first diesel. Ran great drive great everything was good, starts up so easily, as soon as h turn the key. No smoke at idle at all. I did a lot of maintence on it. Oil change, trans filter and fluid, alternator ect ect, lifted it and put 35s on it. Like I said ran Good.

So I drove it 55 miles to a destination, then 40 miles back to another. Went on some unpacked roads and had a little fun but nothing crazy. On the way home she fell on her face. Burping farting put pedal to the floor and she wouldn’t rev up in gear. Got her home but barely. Drove it like this about 15 miles. Next day changed the fuel filter. She was alive again but now she has this , what I call, misfire sound.

At idle it sounds perfect. Start driving withlight acceleration it’s fine. Highway speed 60mph she purrs along. But the in between, the getting up to speed, the half throttle or anything more, it sounds like a gas 8 cyl running on 6, or an exhaust leak.

so I spoke with a friend who’s a diesel mechanic. He gave me a few things to try so I’m gonna tell you what I’ve already done.

Ran the truck off a 5 gallon container strapped to front of truck and eliminated tank. No change
Bypassed fuel filter box and put fuel direct out of lift pump to injector pump. No change
Tested lift pump pressure -Teed in after fuel filter on line the goes to injection pump. 6 1/2 psi at idle and dropped down to about 4 at half throttle while driving from a stop. (Normal?)
Broke glass and spring out of injection pump return fitting no change
Put a clear line from fuel filter to injection pump. Solid fuel no bubbles
Clear line out of injection pump to return line- has small bubbles flowing and idle and sometimes gets frothy bubbles when cracking the throttle open
Injection pump is still retarded from military spec, loosened the 3 bolts and advanced it as much as I could but still couldn’t even meet the line, so it’s still retarded.
I cracked each injector line while running and engine stumbled equally for each one.

please help! My diesel mechanic friend said all return lines will have some air and it’s normal,but I read here that it’s not. could that cause this? I have a video where the noise can be heard it sounds like it has a pulse, only under load tho, getting up to highway speed. Sounds like a miss, but could also sound like an exhaust leak. I’m baffled. I don’t wanna spend 500on an injector pump and do all the laborfor nothing. HELP!!’

 

[NDT]

What is the history on your injection pump? They are full of plastic parts that have a life of about 10 years.

 

[Domterry12]

Injection pump is original. It has some red paint pen marks on some of the screws to show a seal hasn’t been broken. I don’t know if that was from the factory or a rebuilder .

 

[cucvrus]

The internal parts of the injection pump have failed. The only cure is the rebuilding of the injection pump. opinions vary and I will give you mine. I have changed over 100 injection pumps on CUCV's over the years. I had a local rebuilder and they went under after 50 years. The internet has killed off a lot of businesses. I used them for 20 years and had 0 failures. I bought NOS injection pumps brand new never used. I had 3 of the 6 I bought fail in less than 6 months, The other 2 after 2 years. My experience has been you can pay $1000. for one or $400. I have been using Remanufactured DB2 Fuel Injection Pump for 6.2L 6.5L 6.9L 7.3L 5.7L – Diesel Care & Performance for the past 10 plus years and have had great results. A few members here have CUCV's I sold them. I do not recall any of them mentioning to me of injection pumps failing. And as I mentioned in previous threads. I would change the injection pump and go thru the entire fuel system. That is up to and including the fuel tank drop and fuel tank sock replacement. Also change the lift pump. I examined a few of them internally and they are full of crud and worn diaphragms. Sorry to hear about the lift kit. But happy at the same time. The original survivors are getting more scarce with each passing day. The herd of original CUCV's is at a level of protected as far as I am concerned. A few will survive. Thinning of the herd is good. Good Luck. It is a very easy job changing all fuel system parts. Unless the truck runs poorly after the injection pump change I would leave the delivery nozzles alone and drive on. I only ever changed a handful of delivery nozzles on CUCV's and that was because I wanted to. Take Care.

 

[Domterry12]

The internal parts of the injection pump have failed. The only cure is the rebuilding of the injection pump. opinions vary and I will give you mine. I have changed over 100 injection pumps on CUCV's over the years. I had a local rebuilder and they went under after 50 years. The internet has killed off a lot of businesses. I used them for 20 years and had 0 failures. I bought NOS injection pumps brand new never used. I had 3 of the 6 I bought fail in less than 6 months, The other 2 after 2 years. My experience has been you can pay $1000. for one or $400. I have been using Remanufactured DB2 Fuel Injection Pump for 6.2L 6.5L 6.9L 7.3L 5.7L – Diesel Care & Performance for the past 10 plus years and have had great results. A few members here have CUCV's I sold them. I do not recall any of them mentioning to me of injection pumps failing. And as I mentioned in previous threads. I would change the injection pump and go thru the entire fuel system. That is up to and including the fuel tank drop and fuel tank sock replacement. Also change the lift pump. I examined a few of them internally and they are full of crud and worn diaphragms. Sorry to hear about the lift kit. But happy at the same time. The original survivors are getting more scarce with each passing day. The herd of original CUCV's is at a level of protected as far as I am concerned. A few will survive. Thinning of the herd is good. Good Luck. It is a very easy job changing all fuel system parts. Unless the truck runs poorly after the injection pump change I would leave the delivery nozzles alone and drive on. I only ever changed a handful of delivery nozzles on CUCV's and that was because I wanted to. Take Care.

thank you for this response. I’ll be ordering the new injection pump today. Just wanted confirmation before I ordered and I know u know your stuff.
Any tips on changing the injection pump? Any special tool to remove all the lines. And I believe I have to remove the oil fill neck to access the 3 bolts in the front? Is that correct.

 

[Domterry12]

@cucvrus I need the light duty or the heavy duty pump? (4502 or 4544)

 

[royalflush55]

Are you running on biodiesel or #2 ULSD? Bio will clean gunk out of the tank and lines and plug filter. You may have to change filter a few times. I would try pouring some Seafoam into the tank with about five gallons of ULSD and see if that helps first. Sounds like it could have an injector or two not spraying right and causing a miss. Seafoam can help clean dirty injectors.
This is cheap fix if it solves the problem!

 

[Domterry12]

Are you running on biodiesel or #2 ULSD? Bio will clean gunk out of the tank and lines and plug filter. You may have to change filter a few times. I would try pouring some Seafoam into the tank with about five gallons of ULSD and see if that helps first. Sounds like it could have an injector or two not spraying right and causing a miss. Seafoam can help clean dirty injectors.
This is cheap fix if it solves the problem!

I use the regular ole diesel at the pump. When it started I thought it coulda been bad fuel and I had 1/2 tank so I filled it and put diesel kleen in it to no avail, drive it a bunch to flush the system with no luck

 

[royalflush55]

What plugged your filter all of a sudden on that trip when it started running poorly?

 

[Domterry12]

What plugged your filter all of a sudden on that trip when it started running poorly?

I really don’t know. I stupidly didn’t dump the filter out, I just changed it. But it was the filter that came on the truck when I bought it, it looked fairly new so I had left it but who knows how long it was on there

 

[royalflush55]

If it ran fine on that trip, then sluggish, then ok after changing it with a new filter except it has a miss, sounds like something in fuel was bad.

 

[Domterry12]

If it ran fine on that trip, then sluggish, then ok after changing it with a new filter except it has a miss, sounds like something in fuel was bad.

I totally agree. That’s why I ran off a jug with fresh fuel, bypassed the filter, all that. But no change. Maybe the filter plugged and sent something into the injector pump that trashed that too? Constant Air out the injector pump return is the sign too right .
I have a video of the miss noise from exhaust but I don’t know how to post it if I can. Like I said, idle is perfect. 60 mph is fine. Getting to speed, or hitting gas to pass or something sounds like a heartbeat

 

[Keith_J]

If the engine sounds like it is missing, it is a cylinder problem, not injection pump. This IP is a distributor type with only one pumping element all cylinders.

Compression testing can show weak cylinder. A stuck valve can appear as a miss if the push rod drops out.

 

[Domterry12]

If the engine sounds like it is missing, it is a cylinder problem, not injection pump. This IP is a distributor type with only one pumping element all cylinders.

Compression testing can show weak cylinder. A stuck valve can appear as a miss if the push rod drops out.

But upon cracking each injector while running the engine starts to stumble equally for each injector, which would indicate cylinder and valves are working properly? I didn’t do a compression test though. And air coming out of injection pump?
I wish I could send u a video of the noise out of exhaust I’m speaking out. Maybe it’s normal and im crazy!

 

[Domterry12]

@cucvrus @royalflush55 @Keith_J

84 cucv blazer possible miss noise

youtube.com

I know it’s a terrible video please listen closely.

 

[cucvrus]

I agree that is missy very bad and running poorly. It is a poor video and hard to diagnose from it. Hey I'm not there. If I bought a CUCV and it ran poorly and I wanted a reliable vehicle I always went for the fuel system and did a complete overhaul on all the parts. That is after I ruled out the easy stuff that seems you have already done. I limped a few home when the injection pump went out and I had a few that only had a small pin hole in the rubber hose at the lift pump. Have you looked at the lift pump? Is that main fuel feed hose riding on the crossmember? All this needs ruled out and then you go for the throat. But in my years of experience replacing the injection pump has cured many ills. I also notice a lot of dancing around the injection pump issue. It is easy and can be done with basic hand tools. Again. Good Luck.

 

[cucvrus]

If the going gets tough and you need a hand I am at the end of 78 were it splits I 81 exit 90. I get a few vehicles from NJ to work on from time to time. Take Care.

 

[Domterry12]

I agree that is missy very bad and running poorly. It is a poor video and hard to diagnose from it. Hey I'm not there. If I bought a CUCV and it ran poorly and I wanted a reliable vehicle I always went for the fuel system and did a complete overhaul on all the parts. That is after I ruled out the easy stuff that seems you have already done. I limped a few home when the injection pump went out and I had a few that only had a small pin hole in the rubber hose at the lift pump. Have you looked at the lift pump? Is that main fuel feed hose riding on the crossmember? All this needs ruled out and then you go for the throat. But in my years of experience replacing the injection pump has cured many ills. I also notice a lot of dancing around the injection pump issue. It is easy and can be done with basic hand tools. Again. Good Luck.

When I hooked up an aux tank to the inlet of lift pump the rubber hose looked ok, and on the line going to injector pump a pressure gauge read 6.5 psi at idle and dropped to 4psi under load so I feel like lift pump is ruled out.
also the feed line to IP is clear and I can see solid diesel and no air being fed into the IP, but have air coming out of the clear return. Signs point to IP I just wanted to be 100% before spending the money and doing all the labor to turn the key and have the same problem.
And yes the video is crap, I am sorry lol

 

[Domterry12]

If the going gets tough and you need a hand I am at the end of 78 were it splits I 81 exit 90. I get a few vehicles from NJ to work on from time to time. Take Care.

Thank you! Not terribly far

 

[ezgn]

Thank you! Not terribly far

It sounds like it might be in your valve train. You might want to remove the valve covers and check your plastic valve retainers. You might have a broken valve retainer.