Bad Fuel Pump?

[Mos68x]

Has anyone ever had a bad MW fuel pump? I’m feeling like I’m chasing my tail trying to figure out why I’ve lost a cylinder. I finished putting the engine together after having to replace #5 cylinder’s rocker arms, but I’m right back to not having all 6 cylinders. First fire after putting it together and it ran beautiful, but 20 min later after putting the turbo piping on and it was back to running like crap. Letting the engine warm up lessens the effect, but it’s still there. I can’t drive it since it bogs at the slightest incline without any boost. I will try to inspect the injectors again and replace any crush seals that look suspect, I’m just hoping to find something that is stupid simple that could cause this. I’m really hoping that I don’t have to replace the pump since it’ll cost $1900 without the core. Hopefully someone else will have some other idea to check as well.

 

[sandcobra164]

I'd start with the basics that WillWagner has taught many of us. I'd take an infrared heat gun and determine for sure which cylinder was cold in relation to the others by checking the exhaust manifold. Since it's an 8.3 and it's easy enough to do, I would try moving the injector from the cold cylinder and see if the problem follows. If it does, injector is faulty, if it stays the same, compression test is in order. If those two tests show everything is fine and you are 100 percent sure the valves are set correctly, I'd pull the injection pump and have it worked over by a competent injection pump shop.

 

[Mos68x]

Thanks, I didn’t even think of using the IR thermo to see which cylinder is crap. I really hope it’s not an injector since I just replaced all of mine, but I’d still rather have that over a pump.

 

[MAdams]

Sorry I don't have much advice to offer. I just replaced my injectors and forgot to fully tighten an injector hold down clamp bolt. I could hear the compression leak and it got worse with a bigger load. Try the temp gun, swap an injector, verify valve lash and check to make sure the dead cylinder is getting fuel at the end of the injector line by cracking the nut loose while the engine is running

Sent from my SM-G930V using Tapatalk

 

[74M35A2]

Anything can happen. Could very well be an injector as mentioned. There have only been a couple of pump failures here, but they typically result in a no start. You can have a shop verify the pump flow across all 6 cylinders for like $200, includes setting the injection timing to any new spec.

I have an 8.3L Bosch P-7100 12mm “P” pump available if you really want to make it sing, priced about half of your stated replacement cost.

But I would figure yours out first and get it running right before throwing more $ and fuel at it.

 

[Mos68x]

Anything can happen. Could very well be an injector as mentioned. There have only been a couple of pump failures here, but they typically result in a no start. You can have a shop verify the pump flow across all 6 cylinders for like $200, includes setting the injection timing to any new spec.

I have an 8.3L Bosch P-7100 12mm “P” pump available if you really want to make it sing, priced about half of your stated replacement cost.

But I would figure yours out first and get it running right before throwing more $ and fuel at it.

If I so chose to take that pump of yours (after I figure out the issue of course), how much work is there in changing to the P pump? That’s something that I never really considered until now. Aside from that, what kind of performance gains are we talking? If it’s down low where I need it most (<1500 rpm) then I’ll probably consider it, but if it’s only up top (more than 2k rpm) then I’ll probably pass until I see that I really need it.

As I said in the timing pin post (cause I wasn’t paying attention lol) I’ll take the temp gauge to it today and see what I can figure out.

 

[74M35A2]

Bolts right up as long as it is from an 8.3L. The 5.9L ones will also fit and work, but utilize an external oil supply line. Easy either way. P pump can exceed 400hp of fuel flow in near stock trim.

 

[WillWagner]

Clint, IIRC it takes a different drive gear, the pump gear nuts are different sizes so, I am almost positive the shaft/taper is different. Also, again, IIRC, the MW is timed two ways, one with the pin in the engine and pump AND by a letter aligned with the cam gear, still an easy fix. BUT, do the easy stuff first. See if you can find the cold cylinder with the IR gun. If it isn't obvious, there could be a delivery issue like air from junk lines, a plugged filter or low supply fuel pressure. If the overflow valve is junk the engine can and will have a miss. It will seem like it jumps around from cylinder to cylinder. You need to check the low pressure fuel to see what condition the supply system is in.

edit...an outward sign of an overflow valve not holding/letting the lift pump make the correct low pressure is if it runs like crap at idle, it can run smooth when throttled up to rated rpm and will run smooth for a few seconds after letting it come back to idle, then it starts to run funky again.

I don't remember, did the rocker bolt break or come loose? I wonder if somewhere along the line someone has set base timing wrong? Overhead set would be funky, pump to engine timing off....

 

[74M35A2]

Not sure, I removed the entire thing from an 8.3L that it was on. Pump, gear, nut, pump brace, and injector lines. Was going to use it then tripped over the ISL.

Rare for a pump to be bad, especially on just one cylinder. Will be interesting to see the cause of this. Could do a compression or leak down test, did the rockers coming off bend a valve stem?

 

[Mos68x]

Spent all day yesterday looking for that stinkin IR gun, after 30min or so I gave up and just started cleaning lol eventually found in one of the first places I looked lol. Checked the exhaust ports, and surprise to me, it’s the #3 cylinder that is cold. If i can find my 17mm wrench I’ll see if I can crack the high pressure line to the injector and see if I have decent flow (visually of course). If I do I’ll take the after-cooler off and swap injectors with a neighboring cylinder.

The low pressure supply is all replaced, with the exception of the lift pump itself. However, every time that I’ve had to bleed the air out it looks like it’s flowing fine, but again that is visually only, haven’t put a pressure gauge after it yet.

Somehow the rocker assembly bolts came loose on the #5 cylinder, which resulted in a broken pivot shaft. No idea how that happened since I never opened up the motor until diagnosing that moving valve cover bolt. Double checked the torque on the other cylinders and only 1 or 2 were slightly loose (couple Ft-lbs). If have to pop the cover back off again I’ll triple check the valve lash. #5 exhaust push rod was the one that was slightly bent, probably happened when the bolts were coming loose and broke the pivot shaft. I didn’t find any other damage to that cylinder.

Keep the ideas comin, I’ll check them off as I go. Sooner or later I’ll find the issue with your help guys, thanks! I’ll gladly take a bad injector over a bad pump any day!

 

[Mos68x]

At a stopping point right now since I can’t seem to find my feeler gauges. I have fuel flow on all cylinders from the pump, not sure if they are at the correct pressure but for the moment I’ll assume that they are. When I cracked the fuel lines, #3 acted normal but #5 and #6 didn’t. #5 did take a min to warm up when measured with the IR gun. #6 warmed up immediately so I’m not sure what the deal is there. #5 cylinder rockers seem to be tight, so that’s a good reason to check lash, but most of them feel only slightly loose. I’ll pull all of the rocker assemblies and check that the push rods are all straight though since I didn’t think to do that before. At this point I’m wondering if heating the injectors up enough to just flow out on the powder has done this, but I’ll have to wait until I put everything back together and run the engine again to find out for sure.

 

[Mos68x]

Also another thing that I’ve noticed that I forgot to mention. I’m not sure if it is related to the excess fuel screw I turned up, but it does seem to run rich. Not so much by smell of the exhaust, though it does smell like some unburnt fuel is there, noticeable more by throttle response. I’m going to take the excess fuel screw back to stock and see how that does. If nothing else, maybe it’ll help to figure out where the other issue is since it idles at 900-1k. Right now it seems to idle fine, but it is a higher idle than normal so maybe it’ll change when I get it back down to the 600.

 

[74M35A2]

I think you have an injector stuck open from heating them or lash too tight on rockers. Fuel usually helps to keep them cool. Turned up fuel really only comes into play on transitions and then wide open throttle (total rack travel). If you only adjusted the top fuel screw, that is just transition fuel before boost comes in.

Your cylinder that came up slow on temp is not firing.

 

[Mos68x]

I’m going to go out on a limb and say that I think I figured it out. While I was going through all the rocker assemblies, checking them and doing the lash, I had the #5 injector soaking in some gasoline.



Looks like it got thoroughly cooked, crispy fried even, when the pivot shaft and exhaust rocker arm failed. It certainly didn’t look like that when I powdered it, and I know I didn’t get it hot enough to do that. #6 doesn’t look any better and it’s still soaking right now. The comparison injector in the pic is from #3 and looks much healthier. On a side note, the exhaust pushrod on #6 was bent pretty good. Glad I got more than one push rod for replacements. I think it was that way for a while since it was set near close to the right lash before I replaced it.

 

[Jbulach]

Dang, what a mess! Did this truck ever run right since you’ve had it, and do you have any experience with another A2 to know for sure? I can’t imagine whats causing all these problems...

 

[Mos68x]

Dang, what a mess! Did this truck ever run right since you’ve had it, and do you have any experience with another A2 to know for sure? I can’t imagine whats causing all these problems...

It’s me! I have absolute sh1t for luck lol

nah, it ran great when I first got it, minus a lack of power due to the gov springs never being adjusted. Hindsight, I shoulda left them alone and I’d still have all my tires lol

 

[Mos68x]

So much for an easy fix, swapped the injectors and I still have 2 dead cylinders at #5 & #6. Called a “local” shop and they want $350 to just flow test the pump. Fuel flow appears to be the same between all the cylinders when I cracked them loose. I did hear an intake valve stick a couple time when I was trying to start it, but no idea which cylinder. #6 still appears to have a leak past the injector when it running, no idea why that is happening. Might have to consider getting a “new” head at a minimum. Looks like there’s a chance I might have to rebuild this motor after all.

 

[Mos68x]

Good news and bad, think I just now finally figured out the issue I’ve had with my trucks engine. I’ve had a miss on 1-2 cylinders for a while now. I had the truck runnin to charge up the batteries for the house since I just changed them to 24V and something caught my eye (in the dark no less). I had been thinkin that it was an issue with my injectors or the fuel pump, but I just noticed excessive blowby from the valve cover port, and it was white-ish. Looks like I lost a piston or it’s rings. I was really trying not to go any further into this motor than I had to, but now I have no choice. Looks like I’ll be using the in-frame rebuild kit I bought a few months ago after all. Now I just need to find a local shop that can rebuild the head while I deal with the block. I do have one local shop that I deal with so I’ll see if they can do this head for me as well.

 

[74M35A2]

Make sure it is not just water vapor boiling out. I'd do a compression or leak-down test on all 6 cylinders before you rip the engine apart. The compression testing tool is only like $20 to buy, it is a hollowed out injector body with a quick connect on the end. I have a new one I would loan you, but the shipping to get it to you and then back to me would pay for a new one you could have sitting in your toolbox.

 

[Mos68x]

https://youtu.be/Vh8E6QTXL3Y

Smells like raw fuel and motor oil 74. Already called a local shop and they want $480 + $parts to rebuild the head while I focus on the block. I might still get that compression tester since it’ll be a little bit until I can start on the rebuild.