Sputtering Issue

[Optimaldave]

Hi all,

 

So my truck has a sputtering/mis-fire issue that I've been diagnosing and am coming to an end of ideas.

 

It is only when under load (I can rev and hold in neutral with no issue) it sputters and stumbles from 1/4 throttle to half or 3/4 throttle. If I give it very light throttle, or almost full throttle it has no issues but anywhere inbetween is really rough.

 

Sounds/feels like a miss with a slight backfire. Wierd backfire though as it sounds like someone shooting a marble at sheet metal vs the usual loud "gunshot" backfire. Also has the gurgle/pop of a rich system sometimes which is throwing me off as the plugs were very white (may have been white as they were changed after starving the truck to bleed fuel pressure so I could change the fuel filter so I will check new plugs again in future under regular conditions)

 

During my diagnosis/tests today it kept changing from very bad to almost no issue completely randomly. This issue also came on kind of slowly. About 2 weeks ago it had a bad stumble on a cold morning but I was very low on gas so I figured it was that as it went away and didn't happen again. Beginning of the week I noticed a very light stumble when cold going uphill in the morning. About 3 days ago it had a light stumble that stayed through out full temp range. Yesterday and today have been really bad and almost undriveable. Have to drive like a grandma or a mad man as I only seem to have no throttle or full throttle :P

 

 

Tests/diagnosis done:

(In history the system ground refresh has been done)

 

TPS ground was way off (9.2 ohms to ground) so I bypassed the C101,

TPS was off (4.87 input, 0.74 output) so was adjusted and re-tested (4.87 input voltage, 0.82 output, no dead spots)

Changed plugs (were very white tipped but I changed them after starving the truck to relive pressure to change the fuel filter so I will have to check the new ones, Had NGK FR5 now Autolites)

Changed fuel filter

Checked for vac leak with contact cleaner

Checked idle voltage for alt output (14.46V)

Bypassed the ballast resistor (ohmed at 1.4 if my memory serves)

Cleaned the ground behind the taillight for the fuel pump

Pulled the vac line to the FPR and plugged nipples but made no difference.

 

Still to do:

Find a pressure tester to check the FPR and pump pressure

Should I check voltage at the pump?

Check pump sock (want to pressure test first so I can get a pump if needed and only have to pull the unit once)

 

I am thinking the fuel pressure test will answer for me as there is a lot more fuel needed under load so low pressure makes sense but I don't understand why it goes away under full throttle if it is a pump/pressure issue.

 

Any input to other tests would be great.

 

Cheers

Dave

 

*edit*

wanted to add that it starts with no issues, and has a slightly loping idle but nothing abnormal for an older engine.

 

1988 4.0L BA10/5 210,000 KM's (approx, PO had no speedo cable so kind of unknown)

[cruiser54]

You're on the right track. Fuel pressure test is definitely in order.

[vaquaro]

:agree: also check manifold bolts for correct torque (lock-tite green ) and oil leaks from valve cover (rear) flowing into CPS (ESS) on bellhousing ( remove , clean , inspect for melted insulation ) My $.02 :thumbsup:

[Optimaldave]

:agree: also check manifold bolts for correct torque (lock-tite green ) and oil leaks from valve cover (rear) flowing into CPS (ESS) on bellhousing ( remove , clean , inspect for melted insulation ) My $.02 :thumbsup:

 

Manifold bolts have been checked.

 

Didn't look at CPS as I thought a failing cps would give a bad or intermittent no start?

 

 

Having issues getting a pressure tester as they are $50+ here in Vancouver so I really don't want to buy one... So I think tomorrow I may pull the pump to clean/replace the sock as if the pump is bad it'll help anyways. and if sock has no effect then I will suck it up and buy a pressure tester. Will also check the CPS tomorrow if sock has no effect.

 

Cheers

Dave

[Optimaldave]

Ok, So I did some more diagnosis today.

 

Got a fuel pressure tester.

 

Looks like I'm at 28/29 at with FPR

 

and 38/39 with FPR disconnected

 

Small vid of the test, bumps up quick under hard throttle but only drops to the high 20's under quick closed throttle throttle.

 

Could being a few PSI low be causing my issues? Fuel pump sounded louder when I first had the issue but I am not sure if this was just due to feeling that it was an issue or actually louder than before.

 

Any suggestions for how to test while driving as I don't have an issue at idle anyways? Taking off the hood seemed my best bet but I have no doubt it is a PITA working solo. I would love to see the pressure when she is stumbling though.

 

 

Also noticed my CTS (assuming it is the CTS) has been moved to the water pump. Isn't that a 92+ feature? Still has a closed loop cooling system.

 

Thought the O2 sensor looked wierd, but I guess it is a cheap replacement. Could it be causing my issues? ran no tests on it today.

 

Noticed my Knock Sensor has been destroyed. Not sure if I did it today while working or if it happened before. Would having this disconected make it run like piss? Should I replace it, jump the plug, or just leave the plug disconnected?

 

Next day off I'm going to try dumping all the gas just for the hell of it. Though it is fresh gas from a large station, and even has a bottle of STP Fuel Injector Cleaner in the tank as I noticed a tiny stumble while near empty so I threw it in when I re-filled. Should also make accessing the pump easier if needed.

 

Looked at the CPS and it has been wired straight to the ECU but no hole drilled in the firewall which makes me think it was a home job vs a dealer fix. Also didn't test but has never had a starting issue so I will think it is fine.

 

Any input is appreciated.

 

Cheers

Dave

[Optimaldave]

ok. some more diagnosis.

 

Took a video of the pressure tester while driving and causing the sputter

 

start of video - primed/setting up camera 28psi

18 - startup 39 while cranking, drops to 28,, 30 while idle

26 1st gear driving downhill

29 shift to 2nd, pressure drops to 25ish

48 start sputter 32/33psi

57 end sputter

1:08 start up hill 32 psi

1:13 shift/lug going uphill swing 32-28-36 psi

1:18 start sputter stable 31-33

1:48 pull into drive to turn around

2:05 start downhill engine brake

2:38 clutch in around turn

2:58 start sputter

3:10 clutch in downhill (video pretty much done)

 

 

For those who don't watch the vid. The skinny is:

Pressure drops to 26-29PSI when clutch let out from throttle to shift/stop, idles around 29PSI, most uphill load at 30-34PSI, 26PSI while downhill engine braking,

 

Tested FPR again

Line Disconnected, idle, 38/39PSI

Line Connected, idle, 29 PSI

Clamping pressure on return line, pressure drops steadily, faster with FPR connected but always dies out, never goes above 39PSI

 

Also tested EGR Valve today:

Opening test.

Failed, I could never see the pintle even flicker

Closing test.

Passed, soon as I pull on the pintle the engine idle shoots down/stalls if held for too long.

 

Also tried driving with the vac line plugged:

 

No difference

 

 

So seeing as my pump cannot over come pressure on the return line, the FPR seems to be doing it's job, and the EGR has failed on the always closed side. I think tomorrow I am going to bite the bullet and change the pump/strainer ($168 here in Canada, even with an awesome discount)

 

Here's hoping that's my issue as that's all the money I have left :P

 

any other thoughts or tests would be great

 

Cheers

Dave

[cruiser54]

Check the connections at the fuel pump ballast resistor on the driver's side inner fender near the air cleaner. Even run a jumper across the terminals for testing purposes if you feel like it.

[Optimaldave]

Check the connections at the fuel pump ballast resistor on the driver's side inner fender near the air cleaner. Even run a jumper across the terminals for testing purposes if you feel like it.

I've actually been running a jumper since I first had the issue seeing as running at idle and WOT leans to it being the resistor. Apparently not though.

 

Cheers

Dave

[cruiser54]

I wonder what the hose looks like in your fuel pump module. The one between the pump itself and the mounting flange.

 

But, before that, I'd check how good the ground is at the fuel pump module plug under the Jeep.

[Optimaldave]

I wonder what the hose looks like in your fuel pump module. The one between the pump itself and the mounting flange.

 

But, before that, I'd check how good the ground is at the fuel pump module plug under the Jeep.

 

Yeah, I too still somewhat think it is the hose or the strainer but I need all the parts before pulling the unit out so I suppose I will change the whole deal anyways.

 

Will check ground at the pump first though. Already upgraded the ground system and cleaned the ground at the taillight too though.

 

Cheers

Dave

[Optimaldave]

Tested every sensor I hadn't tested before, all passed, so I got a fuel pump and dug into her.

 

Real PITA getting that lock ring off, and after the battle of getting her out... I got the wrong fuel pump :wall:

 

Put it all together again, drove back to the parts store, got the correct one ordered and now I get to wait until tomorrow...

 

on a plus side I got the speedo cable routed correctly and the exhaust hanger tightened down...

 

Man did my beer taste wonderful today :roll:

Dave

[cruiser54]

Tested every sensor I hadn't tested before, all passed, so I got a fuel pump and dug into her.

 

Real PITA getting that lock ring off, and after the battle of getting her out... I got the wrong fuel pump :wall:

 

Put it all together again, drove back to the parts store, got the correct one ordered and now I get to wait until tomorrow...

 

on a plus side I got the speedo cable routed correctly and the exhaust hanger tightened down...

 

Man did my beer taste wonderful today :roll:

Dave

 

I can relate to the beer part for sure.

[Optimaldave]

Well, looks like I'm a complete knob...

 

Got the new pump in (much easier with the original lock ring by the way, the new replacements are a bit larger and much harder to install) test drive still had the issue, so upon contemplating how quickly I can run vs how quick a rag stuffed in the tank can burn... I decided to check everything again. Checked for leaks, no leaks, checked for sensors unplugged/busted, all checked out fine, Checked the dizzy, still rattles.... Wait a sec... Dizzy mount bolt is loose... Torqued, test driven, head slapped....

 

So for all having this issue in future, maybe check the dizzy isn't rattling against the block, or end up with a new pump, to fix a loose bolt...

 

Beer still tasted good though...

 

Dave

[cruiser54]

Dizzy still has the tang on it so it can't rotate?

[Optimaldave]

Dizzy still has the tang on it so it can't rotate?

 

Yes, but I should think the dizzy being able to shake laterally and maybe smacking the block would cause the rotor to have issues making the correct contacts/spinning properly.

[cruiser54]

Dizzy still has the tang on it so it can't rotate?

 

Yes, but I should think the dizzy being able to shake laterally and maybe smacking the block would cause the rotor to have issues making the correct contacts/spinning properly.

 

 

Uh, yeah!! Just wondering if the dizzy's indexing got screwed up if someone had already sawed off the tab.

 

Could you do me a favor? Lsmurphy has a website and is currently posting all my write-ups on it. Could you see how well they open up for you? I'm having issues but I think it's because I'm the author and Word goes nuts when I try to open them. They're under Help and Resources

 

http://jeepseekers.com/

[Optimaldave]

Dizzy still has the tang on it so it can't rotate?

 

Yes, but I should think the dizzy being able to shake laterally and maybe smacking the block would cause the rotor to have issues making the correct contacts/spinning properly.

 

 

Uh, yeah!! Just wondering if the dizzy's indexing got screwed up if someone had already sawed off the tab.

 

Could you do me a favor? Lsmurphy has a website and is currently posting all my write-ups on it. Could you see how well they open up for you? I'm having issues but I think it's because I'm the author and Word goes nuts when I try to open them. They're under Help and Resources

 

http://jeepseekers.com/

 

Tab is still there, bolt just worked loose and was on the last thread :P

Site works great on my iPhone at least. Awesome resource cruiser!

Cheers

Dave

[Comanche1987]

I had the exact same problem with a few vehicles, one of the reasons why I always check the distrbutor cap and see if I can rotate it :wrench:

 

 

One of the most difficult and strangest problems I've found working on cars has to be a 2003 Chevrolet Impala, 3.8L v6, it would make a grinding noise when turning left but not right. I disassembled the front suspension and could not find any problems. After spending 12 hours trying to diagnose I finally had someone drive the car in left circles with the hood up while I ran along side listening. I wanted to slap myself when I figured out it was the starter. The Bendix had gone bad allowing the starter gear to slide out and hit the flywheel on sharp left turns.

[cruiser54]

Dizzy still has the tang on it so it can't rotate?

 

Yes, but I should think the dizzy being able to shake laterally and maybe smacking the block would cause the rotor to have issues making the correct contacts/spinning properly.

 

 

Uh, yeah!! Just wondering if the dizzy's indexing got screwed up if someone had already sawed off the tab.

 

Could you do me a favor? Lsmurphy has a website and is currently posting all my write-ups on it. Could you see how well they open up for you? I'm having issues but I think it's because I'm the author and Word goes nuts when I try to open them. They're under Help and Resources

 

http://jeepseekers.com/

 

Tab is still there, bolt just worked loose and was on the last thread :P

Site works great on my iPhone at least. Awesome resource cruiser!

Cheers

Dave

 

Glad to hear the site worked well for you. I sent him 3 or 4 more write-ups this morning. Did you see the wiring diagrams he has on there? Extremely handy.

 

Glad to hear your Jeep is running well again BTW.