ROUGH running off-idle

[Ωhm]

Were the old plugs fouled out rich? Carbon/fuel soaked.

[dkenitz]

I'm no expert, but the old plugs did look to have a lot of carbon deposits and to me indicated a rich condition.  I'm not sure if that was due to the mix n match set of old plugs, the vacuum leak that existed prior, faulty injectors, etc.

[Ωhm]

If the remaining plugs are similar to the one shown, that's a good sign. Now back to the fuel pump and no pressure on shut down or key on. Anyone care to comment on OP's choice of fuel pump. Carter P74155 fuel pump kit.

[HOrnbrod]

The plugs look fine. There are plenty of posts regarding Carter pumps as being DOA right out of the box. I've always used Bosch replacement pumps and have had good results, as have most of us. FP pressure should jump up almost instantly on startup, and shouldn't slowly oscillate when idling. Fuel filter fresh?

 

The check valve appears non-existent on your rig; it should hold pressure much longer. But there are other causes for rapid fuel pressure drop. There are a couple of test that can be performed to keep from replacing parts not needed.
First with engine up to temp with fuel pressure gauge connected, find the return fuel line where it is rubber and is accessible to clamp with flat blade pliers. Start engine, read gauge, clamp return line. Pressure should go up to 70>90 psi, then turn engine off with line still clamped. If pressure drops it will indicate a bad fuel pump check valve. if pressure stays up or drops a small amount it will indicate either a leaky regulator or injector, if pressure drops steadily it will be an injector.

[dkenitz]

2 hours ago, Ωhm said:

If the remaining plugs are similar to the one shown, that's a good sign. Now back to the fuel pump and no pressure on shut down or key on. Anyone care to comment on OP's choice of fuel pump. Carter P74155 fuel pump kit.

 

All 6 plugs looked about the same.

 

2 hours ago, HOrnbrod said:

The plugs look fine. There are plenty of posts regarding Carter pumps as being DOA right out of the box. I've always used Bosch replacement pumps and have had good results, as have most of us. FP pressure should jump up almost instantly on startup, and shouldn't slowly oscillate when idling. Fuel filter fresh?

 

The check valve appears non-existent on your rig; it should hold pressure much longer. But there are other causes for rapid fuel pressure drop. There are a couple of test that can be performed to keep from replacing parts not needed.
First with engine up to temp with fuel pressure gauge connected, find the return fuel line where it is rubber and is accessible to clamp with flat blade pliers. Start engine, read gauge, clamp return line. Pressure should go up to 70>90 psi, then turn engine off with line still clamped. If pressure drops it will indicate a bad fuel pump check valve. if pressure stays up or drops a small amount it will indicate either a leaky regulator or injector, if pressure drops steadily it will be an injector.

 

Dang it, I should have waited a few more hours to place my Summit order.  Purchased the Carter fuel pump kit this morning along with Taylor wires, a new Actron fuel pressure tester, and a Wix fuel filter.  The previous owner said the fuel filter was changed recently but I'm going to replace it for my peace of mind.

 

Hornbrod, is this the Bosch fuel pump kit you are referring to?:  https://shop.advanceautoparts.com/p/bosch-electrical-fuel-pump-kit-69302/20770761-P?navigationPath=L1*14932|L2*14986|L3*15378

 

The loaner fuel pressure tester from Autozone is no longer reading any fuel pressure from the rail.  The engine will idle, so I'm guessing the gauge is faulty (how many psi required to idle?), but since late yesterday the motor will essentially only idle.  Throttle blips now cause instant sputtering and backfiring.  I'm really thinking the fuel pump is on its last legs.  The truck has 143k miles and I assume the fuel pump is original.  As soon as the new fuel pressure tester arrives I will report back with some readings and updates.

 

As an aside, I was planning on eventually buying a set of reman Bosch 4-hole fuel injectors.  Maybe now would be a great time?

 

Thanks Ohm & Hornbrod!!  

 

 

[HOrnbrod]

3 minutes ago, dkenitz said:

Hornbrod, is this the Bosch fuel pump kit you are referring to?:  https://shop.advanceautoparts.com/p/bosch-electrical-fuel-pump-kit-69302/20770761-P?navigationPath=L1*14932|L2*14986|L3*15378

 

That's it.  

[saveevryjp1998]

I just posted about this on mine this morning. Did you clean and trace your driver tail light ground? I literally had exactly the same symptoms, put a loose clean bolt in a factory hole I found back there since the screw was broke off. Instantantly its idle increased, wasnt low rpm, ran normal, and could stomp the peddle with no hesitation. I would follow that wire and check the ground. Sometimes I have found the rear harnesses have been pinched or worn either between unit body and bed or tank and bed. I bet I have found half of my fleet with bare exposed wires in one of those places over the years. The weirdest thing is the wiring on my trucks almost seems to have no ryme or reason on how its routed back there. I really wonder how it was done clean from the factory before people had a chance to screw them up.

 

 

 

[dkenitz]

20 minutes ago, saveevryjp1998 said:

I just posted about this on mine this morning. Did you clean and trace your driver tail light ground? I literally had exactly the same symptoms, put a loose clean bolt in a factory hole I found back there since the screw was broke off. Instantantly its idle increased, wasnt low rpm, ran normal, and could stomp the peddle with no hesitation. I would follow that wire and check the ground. Sometimes I have found the rear harnesses have been pinched or worn either between unit body and bed or tank and bed. I bet I have found half of my fleet with bare exposed wires in one of those places over the years. The weirdest thing is the wiring on my trucks almost seems to have no ryme or reason on how its routed back there. I really wonder how it was done clean from the factory before people had a chance to screw them up.

 

 

 

 

I am still trying to get the tailgate down so that I can remove the taillight and access that ground.  The tailgate handle is gone and I have not been able to fish out the cables.  I read that two small slotted screwdrivers could possible be used on the hinges.  I hope to tackle that job this week, weather permitting.

[saveevryjp1998]

Heat up the 3 t30 bolts on inside of gate. They will have loctite from factory and 30 years of rust and what not built up. Use a small propane torch, quick and easy. These 3 bolts hold the handle. Once loosend it should drop out a little for much better access to the latch rods that run through the gate to outer llatch mechanisms. Now you can put a lock plier on each carefully to work each side to free up the gate. The ground will be on the driver side. If someone hasnt swapped them out, there should be 2 more t bit heads that match the outers of the light on the inside. Carefully pull the light. They are brittle and easy to chip, remember they are old and hard to find. The ground should be a black wire by itself with a round terminal with I think a Philips pan head screw? Someone help me out, its been awhile and mine snapped off. Anyway its located in about dead center of the housing hole in bed.

[saveevryjp1998]

Its hard to see, but mine is snapped off in bed. On my bed there was a hole that looked factory right below it. I simply took a wire brush to that hole. Then some 80 grit or some rough any size and sanded further. I then found a bolt close to the size. I sanded the terminal which looked to be copper and just literally stuck the fresh bolt in the hole to make contact as a test run. Like magic smooth idle. I bet this is it. I have not ever personally gone through Cruiser's tips, but I know this is one of them. Anyone who has a renix 87-90 needs to go through his checklist first if they are having any issues and are unfamiliar with a renix. I always forget that stupid ground. I know he hinted at checking it earlier on here I read it right after I bought a new lock ring and pulled my pump to swap it out. I was taking pics to document it on here while stumbling upon this in the process and remembered I pulled the tail lights and sold them in the middle of winter. Walked over and bam obvious, felt like a goon but happy I knew it was fixed upon reconnecting. Sometimes its not so obvious. That wire traces back to your sending unit housing and can be bad anywhere in between or at the housing itself on the sending unit. I often think this may have been the culprit for many to end up in the junkyard that seemed in good shape.

[dkenitz]

Thanks very much for the detailed instructions and explanation!  I've done about half of Cruiser's tips so far including the C101 elimination yesterday. 

 

I just went outside to try to get the handle mount disconnected.  I did see that the cables are attached to the top of the mount, but I was not able to get the mount released.  There's a square nut on the studs that I could not break free with heat and a small adjustable wrench.  Any idea what size nut that is in the pic or what socket I'll need? 

 

I also looked over (as best I could) the latch mechanism.  I don't see where I could insert a screwdriver to release the latch. 

[ComancheKid45]

Those are the bottom of the handle bolts. You can access them from the other side with a T30 torx socket.

[dkenitz]

5 hours ago, ComancheKid45 said:

Those are the bottom of the handle bolts. You can access them from the other side with a T30 torx socket.

 

Ohh!!  The bed has a Duraliner bed-liner and I couldn't see the other side.  I was finally able to drop the tailgate and inspected the ground.  The screw was rusted and just disintegrated when I put a screwdriver on it.  I cut the wire and fixed that ground while also going to the fuel sender harness and putting in a 12g ground wire per Cruiser's tip.  The truck would barely start today and would not even hold an idle.  I am even more convinced the pump has given up the ghost.  The new pump should be here by Thursday and I hope to get it installed by Monday.  

[dkenitz]

Well, the poorer performance issue yesterday was due to me forgetting to plug the MAP sensor back in 

I drained the tank today and pulled the fuel pump/sender.  The strainer was heavily gunked up.  Think it looks clogged enough to be the issue?  Are there any parts missing on the sender?  Does anything attach to that return nipple?  The new pump should be here tomorrow.

[saveevryjp1998]

You need to either rebuild that or find another. I would look at your fuel tank too chances are you might be buying a new one. If you bought a new pump, some will come with a filter otherwise I would invest in 1 too. The cover is missing on your zip tied potentimeter. The zip tied fuel pump screen is cool too. I used a stainless steel clamp on 2 of my mjs and it seems to have worked well over the years. Thats a ton of rust. If you leave it that way I guess you could just change your fuel filter, fuel pump screen, and oil every 3,000. Does your oil look that rusty?

[dkenitz]

The oil doesn't look rusty at all and I have a new fuel filter coming tomorrow hopefully. I am all for replacing the fuel tank with a new steel one off Amazon but i want to wait a bit and just get the truck back on the road at this point. Probably will plan on it next oil change. Thanks for the advice!!

[SVPete]

Saw your photo and it reminded me of a problem we had with a CUCV during Desert Shield. Paint chips (from the interior of the metal fuel cans) were clogging the filter on the end of the pickup tube. It took us a while to figure that out.

 

Truck ran fine at idle, but when you tried to drive, it would die. We cleaned out the tank and cleaned off the pickup filter and the problem was solved. When the symptoms occurred on another vehicle a few months later, we went straight to the fuel tank and solved the problem.

 

The things you forget and then remember. Man, the bumper number was A122.

[dkenitz]

Latest update: I just swapped in a fresh fuel pump and fuel filter....... no change. 

 

I took advantage of an eBay coupon earlier and ordered a set of reman 4-hole injectors.  Any other ideas at this point??  

 

Dustin

[SVPete]

Did you clean out the tank? If not, I suggest you look at your pickup filter again just to make sure it isn't clogged up again.

[dkenitz]

5 hours ago, SVPete said:

Did you clean out the tank? If not, I suggest you look at your pickup filter again just to make sure it isn't clogged up again.

 

Good idea.  I did not clean out the tank this time and will pull the pump back out and check the strainer.  I may try to rig the pump up outside the tank briefly to see if there's a change.

[dkenitz]

Where does the camshaft position sensor (signal sync generator) plug into the harness?  Mine appears to have been disconnected?

 

EDIT: Read up some more and it looks like the Renix motors should run fine with that sensor disconnected.

 

[dkenitz]

I pulled, cleaned, and replaced the crankshaft position sensor. The truck ran great for longer than it ever has since I've had it. The symptoms eventually returned but I believe this may be the culprit. The CPS was quite worn and I have a new Mopar CPS on the way.  

[Ωhm]

Your persistence is going to pay off one day.

[dkenitz]

39 minutes ago, Ωhm said:

Your persistence is going to pay off one day.

Hah, thanks Ohm! I sure hope so. So far it has been a fun but frustrating learning curve.

[cruiser54]

17 hours ago, Ωhm said:

Your persistence is going to pay off one day.

No kidding!!! I'm impressed.