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MayDay!! - Hard Accel Killed Idle


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You don't need gorilla torque for manifold bolts.  If you do, you have more problems to deal with.

 

Now, the pinion nut on a Dana 80, that's gorilla torque...

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I just laid under the truck with a box end wrench to get all of my bottom ones.  That said I have long skinny arms, so that likely helped.  It would be way easier to just remove the airbox and come in from the side.  

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1 hour ago, pizzaman09 said:

I just laid under the truck with a box end wrench to get all of my bottom ones.  That said I have long skinny arms, so that likely helped.  It would be way easier to just remove the airbox and come in from the side.  

Was you exhaust still there?  I'm thinking that dropping that first would probably help, and you do have to at least disconnect it anyway.

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14 hours ago, AnotherOldJeepGuy said:

Was you exhaust still there?  I'm thinking that dropping that first would probably help, and you do have to at least disconnect it anyway.

Yes, I did it with everything in place with the wheels on the ground.  I may have used some sockets too, I don't particularly remember.  I know I used a ratcheting box end wrench on some, and had to install a bolt in the back hole as the stud and nut had backed out completely and was missing.  The front lower stud may be easiest to reach from above in front. 

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  • 3 weeks later...

OK I got after it again today and finally found a combination of body position and tool, and got to the last two manifold bolts.  All are snugged up now.  The last two didn't really need much, maybe 1/4 turn.  No change.  Truck is still very sick.  But at this point  I have eventually found how to touch each of the bolts, but I'm not yet convinced I have the reach or expertise to get them all back in if I were to take them all out since 3 or 4 of them I got a wrench to, but not my hand.

 

Actually put the back up on stands so the wheels were not touching the ground and looked underneath while it was running.  Still cannot find a leak.  I did check with a local shop that said, for $200, they would do a full diagnosis and tell me what is wrong.  Given the amount of time I have spent and not found the problem, I am considering that plan.  I'd feel a lot better about trying to pull off the manifolds if I actually know that is where the problem really is.  Or it's at least possible they will find a problem that is easier to fix.  At some point my Advanced Shade Tree Mechanic degree isn't enough!

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  • 2 weeks later...
1 hour ago, AnotherOldJeepGuy said:

Can you install the EGR Delete Kit without removing the small pipe from the exhaust back to the intake, or is it a requirement to do both?

We took it all off. We didn't use a "kit" we just made our own.

 

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Posted (edited)

So the reason I am asking about the EGR delete is that the shop I took it too for diagnosis said the problem is the EGR Vacuum SOLENOID.  For my 4.0 MJ it looks like the part is 3300 2298.  Given the circumstances that seemed to cause the failure, I can't say I am all the convinced, but, I'm willing to gamble a little.  But I don't find this part number at the places around me (AutoZone, Napa, O'Reilly) or at Rock Auto or Summit.  So I am assuming if I can't find one and this really is the problem, the other choice is to delete the EGR, but I am wanting to know if I can remove the EGR valve and block it off without having to also remove the intake and exhaust and remove that interconnect to try and fix my problem.  One job is way less work than the other and if I CAN fix it with the smaller job, I'll take that option.

 

Alternatively, is there an aftermarket that will replace 3300 2298?

 

1767787053_SOLENOID-EGRVacuum.jpg.62b10487aa1f934f8a59a65bba0a0fb4.jpg

Edited by AnotherOldJeepGuy
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5 hours ago, AnotherOldJeepGuy said:

Can you install the EGR Delete Kit without removing the small pipe from the exhaust back to the intake, or is it a requirement to do both?

If you leave the EGR tube you will have an exhaust leak. You need to pull the pipe and install a plug in the exhaust manifold.

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The shop that did the diagnostic did repair these two hoses (Cabin Air Control and Heater Control).  These were in bad shape but still connected.  I really can't believe either of these caused the major problem, cause they have come loose before and I lost control of cabin airflow control, but nothing else happened and the engine ran fine  when they were loose.   They also replaced the two small hoses that connect at the back of the Air Box.  These were also very bad, but again, they have been bad for a while and the engine was running great.

2104338340_newhoses.jpg.86778a07e6c89f87dfd848fe2f141cc7.jpg

 

 

The question I have is about what they also did after diagnosing the EGR Solenoid was bad.  They didn't have a new Solenoid, so to bandaid this problem they "bypassed" the EGR by pulling the hose indicated below off the EGR Valve and capping off the hose.  It does idle now albeit not as smooth as it used to, and I do have cab airflow control, so obviously I did get improved things.  My question to the experts is, with the hose to the EGR Valve disconnected and capped off, what should I expect to happen?

 

 EGR_ISO.jpg.644f1d460a03f108586b6ed9ee4874a4.jpg

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Got the NOS EGR Vacuum SOLENOID and installed.  Some improvement, still not running right.  A bit rough, shaky accel rather that smooth.  So if there's anyone out there that hasn't had enough of this journey, I have more questions.

 

1.  Should I see the EGR "plunger/shaft" move in and out every time I rev up the engine or just sometimes?  It moves sometimes.

 

2. While I was revving to watch for question 1, I noticed that if I rev it up enough, as soon as I let go I hear a noise [pop].  I don't know for sure what it is, but you if you can listen to this 4s video I captured, and listen just as I let go of the throttle, you can hear it.  It this a small backfire?  If it is, doesn't this suggest anything in particular.  If it isn't, can anyone say what it is?  It's a single knock of somekind that seems to be coming from the exhaust manifold as best I can tell.

 

Since my exhaustive searching have not found any vacuum leaks, and I have tightened everything, what else might have been caused by my initial maneuver (does anyone remember all the way back to my OP :dry:)  that started all this?  Could I have somehow thrown off the timing just enough to let it run, but run choppy?

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On 5/23/2026 at 6:57 PM, AnotherOldJeepGuy said:

Should I see the EGR "plunger/shaft" move in and out every time I rev up the engine or just sometimes?  It moves sometimes.

 

EGR operates at part-throttle conditions. Closed at idle and WOT. and that pop does sound like a backfire. Does the exhaust smell a little richer than it used to? And if you have someone do a quick rev like that for you while you stand at the tailpipe, do you hear it there?

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10 minutes ago, Gojira94 said:

 

EGR operates at part-throttle conditions. Closed at idle and WOT.

Ah, well then it would appear that this is at least a clue since when I manually pull the throttle and watch, and I am not getting anywhere near WOT when I do this, I should be seeing the plunger move, and the last time I looked it was not moving.  I have seen it move, but not always.

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I think I'm in agreement with @Eagle_SX4 that you're over-fueling somehow. Whether cracked exhaust manifold with O2 seeing what it thinks is lean and adding fuel, or less likely but possible ruptured diaphragm in the fuel pressure regulator. If you pull the vacuum line off the FPR and plug it with your thumb (the line, not the regulator itself) normal response would be a dip in RPM/ slight bog as it started to chew on more fuel at 39-ish psi instead of 31-ish at idle. If there's no change, that would be a clue. If you are and have been over-fueling during all this adventure, the plugs would show evidence of fouling/ heavy soot and might even be a little wet. If over-fueling ends up being a big part of the issue, new plugs would be in order once the issue is solved.

 

Not to give you more homework, but what kind of shape is the rest of your secondary ignition in (wires, cap, rotor)? Weak ignition parts exacerbate over-fueling conditions.

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I can't 100% rule out a crack, but I have hunted extensively trying to find one and can't.  And the shop that did the diag didn't find one either, so it is just difficult at this point to justify the major disassembly that might be beyond my expertise yet.

 

14 minutes ago, Gojira94 said:

Not to give you more homework, but what kind of shape is the rest of your secondary ignition in (wires, cap, rotor)? Weak ignition parts exacerbate over-fueling conditions.

I replaced all of these about 3 months ago, and long before this incident occurred.  Was running perfectly after replacing these until the "maneuver" that broke something.

 

Just making sure this is where you want me to pull off the hose (from a pic from a year ago when I was replacing injector seals).  I can pull this off while running without  spewing gas?

 

image.png.7b4f685d56c5cd5850cf912387b499d8.png

 

The shop "bypassed the EGR" while I looked for a new solenoid.  I thought they just disconnect and capped off one hose but it might be that they also disconnected the hose under the transducer, but so far I can't see down there good enough to be sure.

image.png.8f37806a3207478f91a4c141127c765e.png

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Yes, pull the vacuum line off of what you have in your pic and plug the line with your thumb.. Try it not running first, just in case it's leaking. If it is, the excess fuel would be drawn into the intake manifold by vacuum.

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Posted (edited)
27 minutes ago, Gojira94 said:

Yes, pull the vacuum line off of what you have in your pic and plug the line with your thumb.. Try it not running first, just in case it's leaking. If it is, the excess fuel would be drawn into the intake manifold by vacuum.

OK.  Pulled off the hose not running first and nothing wet there.  Put it back on and started.  Then pulled it off again.  I could immediately hear it sucking in air at the hose but didn't hear any change in the engine.  Then when I block the hose with my finger I can feel a noticeable vacuum pull on my finger but I still don't hear any difference in the engine.

 

I also noted, unrelated to this FPR test but just before it, if I pull the throttle at the TB very slowly I can pretty much stall the engine as soon as it is away from rest position.  But if I pull it a little more quickly so that I pull quickly it past that "just off rest" position quickly I might notice a very small hesitation but it  doesn't stall.

Edited by AnotherOldJeepGuy
remove my double (doesn't not stall) negative
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Oh BTW I got a small mirror and was able to confirm the hose is connected at the underside of the EGR transducer.  Also noting that the EGR plunger seems to either move when I start it and continue to do so until I shut down and start again, and on the next start it is no longer moving with I bump the throttle at TB.  So whether it moves or not seems to be a roll of the dice on any given start up.

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More information gained, that's a good thing. I wouldn't worry too much about EGR for the moment. It's a closed cycle system and has no vacuum leaks, confirmed. The TPS finding is more telling. Potentiometers can develop dead spots and errant output. If you have a DVOM, you can check what it's doing - @NickInTimeFilms to the rescue again:

 

 

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