Jump to content

Miss at all RPMs


Recommended Posts

  • Board Of Directors

Alright guys I am experiencing a miss at all RPMs. It is pretty noticeable near the engine with a knock, but is extremely noticeable at the exhaust. It is easy to feel that the exhaust is "puffing" per say. Now I just replaced the injectors with a new set of 125hp sacs, but the miss was prevalent before the injector swap. The swap did not make a difference. Everything sounds the exact same as before the swap. I have fuel squirting out of each connection at the cross over tubes while running.

MoparMan and I spoke on the phone earlier and have decided to take a systematic approach to resolving this issue.

Ruled out: 1. Injection pump: Always supplied good pressure, less that 10K miles and miss seems to only be in one cylinder. 2. Injectors: Swap made no difference.

Possibilities (Almost endless): Burnt/ broken valve, broken piston or piston rings, clogged cross over tube, valves way out of adjustment

 

I should receive the truck Friday from being painted and I can start diagnostics. 

The plan: 1: Pull valve cover and quickly check valve lash - just make sure somewhat close to spec. 2. Use an infrared heat gun on the exhaust manifold right were it come out of the head to try and narrow down which cylinder is missing. If that does work I will pull the cross over tube and replace it (I already have 1 new one that will ship out Monday). If that does not fix the issue I will do a compression test on that cylinder to determine if it is the bottom end or the head.

If the heat gun does not find a "cold" cylinder I will pull all injection lines and cross over tubes, then clean each tube and try to determine if there is debris in one of them. If I can not find debris in any of them I will replace them with the new one, one at a time. If that proves inconclusive I will perform a compression test on all 6 cylinders. 

If any of the cylinders are low on compression I will pull the head and determine what is wrong internally.

 

Any suggestions on the procedure or something else I can do to diagnose what is wrong with this thing??

Edited by TFaoro
Link to comment
Share on other sites

I'd go with the compression test first.. Ok, do this first:

Old trick.. loosen (one at a time) fuel line connection at each injector. (be very very careful here, don't need a finger cut in 2 by HP fuel spray)... and listen for a change in the engine. When you DON'T hear a change, you've at least isolated the correct cylinder. I'd shut off the engine to tighten the fitting up... then go on to the next one.

You'll then know which hole is dead, and that's the one I'd compression test.

Link to comment
Share on other sites

  • Administrator

I'd go with the compression test first.. Ok, do this first:

Old trick.. loosen (one at a time) fuel line connection at each injector. (be very very careful here, don't need a finger cut in 2 by HP fuel spray)... and listen for a change in the engine. When you DON'T hear a change, you've at least isolated the correct cylinder. I'd shut off the engine to tighten the fitting up... then go on to the next one.

You'll then know which hole is dead, and that's the one I'd compression test.

 

Between these two test compression and fuel line loosening will give you two different test pointing to the same cylinder.

 

Like I was explaining to Tyler is that if you at least have two different test showing the failed cylinder then you know where to start at.

Link to comment
Share on other sites

Between these two test compression and fuel line loosening will give you two different test pointing to the same cylinder.

so you think this is good, or a waste of time?

If the loosening isolates a cylinder, It doesn't necessarily mean burnt valve, piston,.. it doesn't even eliminate a

bad IP... It only tells you which hole he needs to inspect.

THEN, a compression test will tell you if something isn't kosher down below.. If good compression, then it's gotta be in the fuel.

Link to comment
Share on other sites

sometimes, I can 'feel' the difference in the fuel line themselves. Each pulse should feel like a 'zing' under your fingertips.. and a blocked injector will make the fuel line more like a 'thud'.. highly unscientific... but I've found more than one this way over the years.

This is just placing your fingertip on the line somewhere... preferably before you loosen any fittings.. (to make sure you aren't going to get hurt)

Link to comment
Share on other sites

  • Administrator

so you think this is good, or a waste of time?

 

Good. That what I was explaining to him about getting 2 different test show the problem. Then you know your on the right track. Then the compression test will tell if its a cylinder issue or a fuel issue too. It might be a plugged cross over tube or maybe a cylinder issue. But we need the testing to be done. Like Tyler was going to buy a full set of crossover tubes they are not cheap so figure $25 a piece times 6 gets rather spendy fast. So why not do some basic test and isolate some of the issue and find out what you need before buying a bunch of stuff.

 

Just thinking about it Tyler you might ask Pepsi71Ocean about his compression tester.

Link to comment
Share on other sites

  • Board Of Directors

He hasn't been on since September... I would love to borrow it though. MoparMan can you PM me his number or something so I can get a hold of him? I tried cracking the lines and can not tell exactly which hole is causing the miss. I have a pretty sharp ear for those things and just can't rule out which one.... But to me it seemed like #3 or #5. I will give the "feel" a test as well.  I guess if it is something clogging a crossover tube it is likely that more than one hole got debris in it. 

Link to comment
Share on other sites

yup testing steps sound good, crack lines and see which doesnt change, it will be noticeable. once the cylinder is identified, swap crossover tube with known good one and move forward. if still bad, check valve lash on that cylinder, if still bad compression check it. if that fails, the head needs to come off and valves and seats and head inspected for damage/cracks. if a piston has bad rings you can drop the pan, take oil tube off then loosen the pistons conrod end and push piston out, do a quick ball home on the cylinder if not damaged and replace rings, reinsert piston (make sure bearings arent disturbed) put new conrod bolts in and retorque, new headgasket studs and torque em down. if the head comes off, its a two man job or a hoist to remove replace the head without damaging the gasket. while its off have the head checked for flatness.

hope its a simple fix boss!

Edited by CUMMINSDIESELPWR
Link to comment
Share on other sites

  • Administrator

He hasn't been on since September... I would love to borrow it though. MoparMan can you PM me his number or something so I can get a hold of him? I tried cracking the lines and can not tell exactly which hole is causing the miss. I have a pretty sharp ear for those things and just can't rule out which one.... But to me it seemed like #3 or #5. I will give the "feel" a test as well.  I guess if it is something clogging a crossover tube it is likely that more than one hole got debris in it. 

 

In the 911 contact list...

http://forum.mopar1973man.com/index.php?/topic/4768-bass-river/

Link to comment
Share on other sites

  • Board Of Directors

Lines leaking at the head? Since my 100 hp injector install my lines are leaking and I can't blow smoke...distorted cross over tubes...

No leaks right at the head, and I believe they are seated well into the injectors because of the procedure I used to install the injectors. (Snugging the injector line before tightening the injector hold downs)

Link to comment
Share on other sites

so let me get something clear.

the OP stated a miss, is this a totally dead cylinder or a cylinder that is not lighting up everytime? if it is totally dead then its one of three things, no compression or fuel delivery or possible burnt/cracked/bent valve (which would go back to compression loss)

my experience with dead cylinders, when you see puffs of smoke @ idle, (white to bluish white) means she is getting fuel. It just isn't getting lit.

....usually goes away @ speed, since the other hot exhaust eventually lights it in the exhaust pipe.

On a turbo engine, a burnt valve, flat cam, REALLY SCREWS with the operation of the turbo, and tons of black smoke/low power are evident.

Had a JD tractor 466 turbo, that had just 1 rocker arm wear through, (exhaust) and was the smokiest dud. ( freight train type coal)

Link to comment
Share on other sites

  • Board Of Directors

Just to clarify a bit... I have not been able to drive the truck around since the injector install, but like stated above this miss was prevalent before the injector install. When idling and on 6cyl high idle I have Zero smoke coming from the exhaust and no blowby with the oil fill cap off (With new and old injectors). 

With the old injectors while driving there was no excessive smoke of any color from the exhaust. The knock seemed to quiet down some with higher RPMs though. 

When idling with the new injectors all 6 runners coming out of the manifold were hot, leading me to believe it is not a complete miss, but more of a partial miss and a cylinder not getting enough fuel.

 

The turbo lights just fine and easily pushes 45+lbs of boost (Makes me think it is not a flattened cam at least not on the exhaust side.)

I don't have excessive smoke wile idling or revving engine when it is hot or cold (Cam not flattened on intake side because there is air getting in to burn fuel)

There is no blowby, which I know is not a definitive test for whether rings are broke or a piston is cracked, but I would think there would be some.

Without testing some things I will not know for sure but I am fairly convinced it is a fuel supply issue. With a VP that has less than 10k, always fed 2 stroke, FP at 19 idle and minimum 10 at WOT I don't think the VP is shot already. The injectors are new from DAP so they should be good. This only leaves cross over tubes

Link to comment
Share on other sites

×
×
  • Create New...