dkenitz

Also I have bypassed the ballast resistor in an attempt to simplify things.

Here is a video of one test where I was blipping the throttle and it's sputtering. After this test the gauge stopped registering any pressure, even with the engine idling. So, not sure how accurate the gauge was in this video. https://www.dropbox.com/s/banipl81c2wyj4o/20180422_155524.mp4?dl=0

I'm starting to believe the issue is a dying fuel pump. After I first start the motor, it will rev freely (and sounds perfect) for the first set of throttle blips. Then the sputtering, backfiring, hesitation returns. At this point I plan on ordering: Taylor 84048 wires, AutoZone's Duralast Gold distributor cap w/rotor (brass terminals), and a Carter P74155 fuel pump kit. Thoughts?

Thanks Pete, very helpful info!!

Pardon my lack of searching...easily swapped into my '88 4.0 5spd w/o tach?

Thanks for that information, I'll go ahead and order new wires, cap, and rotor since I have no idea how old they are. Cruiser, what do you think of those fuel pressure readings above? Close enough to spec to rule out a fueling issue? Also, could you recommend specific wires, cap, and rotor? Is local auto parts store quality good enough?

It's on the driver's fender side of engine bay:

Latest update: installed all new vacuum hoses including CCV (minus MAP for now), bypassed the fuel ballast resistor, changed the spark plugs to NGK 7252 (found a mix of 5x NGK BKR5ES and 1 random Champion), and inspected the sensor grounds...though ran out of time to solder them together as well as eliminate the C101 connector. The sensor grounds looked good though. I will still solder them together as well as eliminate the C101 (hopefully tomorrow) but I was surprised how non-corroded and healthy they looked. On the first start the motor revved fairly freely without the hesitation and missing as it did before. I got excited, but after a few mins the hesitation and sputtering returned with throttle application. I did floor it once and it hesitated but did start revving freely. I also measured the fuel pressure at the rail today. At idle the pressure was ~29 psi (+/- 0.5 psi) and with the FPR vacuum line unplugged, the pressure was 38 psi. I believe the specs are 31 psi @ idle and 39 psi with the vacuum line detached. Do these values indicate the fuel pump is failing? Dustin

Thanks for chiming in cruiser! I'm waiting on NAPA to let me know the vacuum harnesses are in and I'll be doing the sensor ground upgrade hopefully tomorrow. Is there anything else obvious I'm missing at this time? Dustin

Thanks for the suggestion Slug! I've come across some posts on temporarily plugging the egr valve vacuum hose in order to keep it closed and check for improvement. Would that work in this case? If so, which hoses/ports specifically do I need to block off? The separate vacuum transducer is confusing me a bit. Dustin

Hi all, First, I'm very glad to have found this forum!! I've been doing a lot of searching and reading here, and I'm blown away by the knowledge and 'niceness' of the members (special thanks to Cruiser54)! I recently purchased an '88 Comanche 2wd (4.0/5spd Renix). The truck is running extremely rough, except at idle. With any amount of throttle (though I don't believe I've floored it yet), the motor will stumble, misfire, and today for the first time, I heard a backfire. So far I have: cleaned the dipstick ground and associated terminals, replaced both battery cables, replaced (and adjusted) the TPS that was not sweeping smoothly, replaced the firewall ground per Cruiser54's tip, throttle body appears to have been recently cleaned, the MAP hose is good per my quick mouth vacuum test, cleaned out the C101 connector, and used contact cleaner on all the electrical connections I could find in the engine bay. I still need to do the sensor ground upgrade and eliminate the C101 connector as I get variable resistance when wiggling the wire harness as well as C101 connector. I also have ordered the vacuum harnesses as there are multiple broken and missing vacuum lines (see pics). There are mangled wires running to the distributor as well which I need to replace (see pic). After doing some more reading I have removed the valve cover and attempted to check the distributor indexing as it appears the cap and wires were recently replaced. I'm not sure if the distributor itself is new or old but I'm thinking it could be old as it says "Lucas" on the sticker (see pic). I removed the cap and checked for rotor alignment at TDC but stopped before actually re-indexing the distributor. The rotor appears to point at 5 o'clock when at TDC, which seems correct. If it was off a couple teeth could that cause the extremely rough running? I'm wondering if I should go ahead index the distributor (or replace if necessary), or if I should wait until I have eliminated the C101 connector and sensor ground upgrade? Also, one of the two throttle body holes is open (see pic). Is a vacuum line supposed to go there as well? Am I missing anything obvious in figuring out this rough running issue? Any advice would be appreciated. Thanks in advance! Dustin 20180417_122913(1).mp4