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Something to check if down on power/mileage

DP96XLT

Well-Known Member
Joined
November 29, 2019
Messages
123
Reaction score
49
City, State
New Berlin, WI
Year, Model & Trim Level
1996 Explorer XLT 4WD
Hey guys, I figured I would post this because I will honestly admit I have never ran across this kind of issue on any engine/car I have owned/worked on...

First off I have a 43k mile 1996 Explorer XLT 4dr/4wd with the 4.0l OHV v6 engine. Basically like new, did plugs, wires, PCV valve, air filter, etc.

I originally posted about it when I got it back in November of last year and have been doing stuff to it since, but I have always had abysmal gas mileage and power has really lacked. It was so bad the wife even asked if I could do something like adding a supercharger to it. (yeah, I married the right woman)

But, honestly, no matter how easy on the throttle I was I couldn't get more than 210 miles to a tankful (basically around 12mpg). With all my upgrades I was able to eliminate any sort of "drag" being the issue (new brakes all around, all synthetic fluids, checked hubs/axles/bearings/etc). I checked the throttle position sensor, coolant temp, intake temp and everything else and it all checked out fine. Also no diagnostic codes, no misfires, per scans the fuel trims were in-line and in general it seemed to run smooth and even enough. Always had that weird exhaust/engine sound that I was told made the Cologne engine kind of a unique thing.

Now, I changed out the muffler system for a Gibson cat-back. It changed the exhaust tone, but didn't change the power/gas mileage (I didn't like the tone with the Gibson chambered muffler so I switched to a Borla XS straight through). I switched to a K&N intake (got it for $125 new off Amazon so why not), again, no change.

So, about the only part I didn't change was the ignition coil. I did the standard spark test and it was nice and bright enough on all 6. But, as a last hail-marry I decided to put on a new coil. Found an Accel 140035 coil on ebay sold by Accel themselves for $50. Decided since it was basically cheaper than a Ford OEM coil, why not.

Got it in, 10 minutes later it was installed and upon starting it up I could tell it made a world of difference. Immediate start, even smooth idle (smoother than before), exhaust tone was totally different and in general I was surprised. Took it for a drive and it is a totally different truck. It has decent power and it is no longer a dog. The one issue I have is that the tranny seems to be "lazy" but I do realize being a OHV it isn't meant to rev to the moon all the time and the transmission programming is optimized to utilize the massive torque-band the engine puts out. I (and I am sure a lot of others) are just used to powertrains downshifting as soon as you WOT regardless, where-as this setup at times most certainly determines you are in the right gear already and refuses to downshift on a pedal to the floor request (there is an on-ramp downtown that is a decent 25-30 degree upward grade and if I am going fast enough onto the ramp when I WOT it won't downshift and rides out the current gear even locking up the torque converter while in WOT as an example).

I drove a few tank fill-ups and I am up to 18-19mpg. And that is with being somewhat aggressive with the throttle at times. I also noticed the exhaust tone changed quite a bit and I might have not minded the Gibson muffler after all since it seems somewhat quieter than it was before even with the Borla.

I can say it is far from the dog power-wise it was. I would put it on-par with most torquey v6s. I did have a buddy do some tests on the coil (he has the equipment to test coils and get readings while firing) and he said it was putting out like only 6-8k volts. Said it most certainly was probably an internal issue (figured it was cracked potting from age) since it looked fine on the outside and I as well as he tested the resistance and all coils were "in range" per spec.

One other thing I noticed before the coil pack was whenever I had the headlight on and put on the directionals the engine would change rpms in time with the directionals (putting on the hazards were even more noticeable). Once I swapped the coils that weirdness went away and no kind of current draw affects the way the engine runs.

Moral of the story, coil packs are cheap, if you checked everything else, swap it out.

I will do another write-up on the stereo system upgrades (nav headunit, amplifier, subwoofer), charging system upgrades (2-gauge and 4-gauge wiring along with 240amp alternator), lighting upgrades (12-gauge hot-wire harness and higher output bulbs) all with in-depth info on how/where I ran wires, connected into the stock power distribution block and in general made everything seem as if it was there from the factory.
 



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Interesting ....I'm sure my 95 (same engine) has the original coil pack....with a bit over 3X the mileage your infant Explorer has....for $50 I'll ad it to my list...
On the K&N filter I'm surprised you didn't notice improvement....I put one on my old 94 Ranger (same 4.0 ohv engine) and it was obvious improvement. Haven't got one for Explorer as this is mainly for off-roading and doubt a K&N filters out fine dust particles as well as paper.
 






Honestly since I did the K&N intake while it wasn't running right I couldn't tell. I also put on the optional K&N pre-filter sleeve they now offer. It is water-resistant and has quite a fine filtration ability.

I have no power issues at all now. Outside of the weird programmed shifting strategy, I am quite happy with how it runs and how much power it has.

I just noticed while running it tonight once I got done with the lighting upgrade that the upper seal on the transmission cooler in the radiator is seeping. Nothing major, just hope it is a simple fix.
 






Re shifting, have you made sure there's zero play in the gas pedal <> throttle cable connection? If there's any play, then it's likely that when you floor it, the butterfly in the throttle body isn't opening all the way.
 






Have you replaced your O2 sensors?
 






Thanks for the reply guys...

In regards to the throttle-cable, there is no play. I did the cable-mod with two zip ties to bring the pedal up higher, but ultimately removed one because it was too high, but I have verified that when you WOT that the throttle opens all the way (maximizes the linkage before the pedal gets to the floor).

I have not replaced the O2s, primarily because on scans they react "normally" and with so little mileage (43k) I would be amazed if they were bad already.

I will put a pair of new O2s on the list for parts to replace the next time i change the oil if they are a known point of failure on these engines.
 






Thanks for the reply guys...

In regards to the throttle-cable, there is no play. I did the cable-mod with two zip ties to bring the pedal up higher, but ultimately removed one because it was too high, but I have verified that when you WOT that the throttle opens all the way (maximizes the linkage before the pedal gets to the floor).

I have not replaced the O2s, primarily because on scans they react "normally" and with so little mileage (43k) I would be amazed if they were bad already.

I will put a pair of new O2s on the list for parts to replace the next time i change the oil if they are a known point of failure on these engines.

It's not that the O2 sensors are a major known point of failure, but they do wear out. 43K is low mileage for even unheated/2-wire O2 sensors to go bad (unheated O2's have a live expectancy of around 60K and heated/4-wire O2 sensors typically last around 100K-120K) but as they can fail in a way that doesn't set any DTC's (and they effect your fuel trims) they can adversely effect fuel economy. Do you have a way to measure your fuel trims? You are throwing a lot of money away on parts w/out knowing where your actual problem lies. It would be better to spend the money on having a good mechanic diagnose the problem.
 






I’d consider the o2s. Time has an effect, not just mileage.
 






My trims are negligible (like within 1-2%), that is why I wasn't worried. The swing on the O2s seem "normal", but I am not used to monitoring these systems and don't know if they are "reliable" via readings...

I do know some factory O2 sensors are known to get "lazy" where-as they seem to be fine, but ultimately are not accurate enough. That is why I was happy when most manufacturers went with wide-band O2s...

BTW, I am a LT1/LS1/LSx tuner... as well as a dozen or so of other systems (FAST, DFI, Haltech, etc)... I have even developed at one point a DFI wideband "autotune" system back in the late 90s, so I am well-versed in ECUs and PCMs as well as the associated sensors, including O2s.

I figured I would ask those that have dealt with these things a lot more as their "primary" focus. I know for fact Bosch O2s are complete ****e on 90s-early 2000s GM PCM systems (very inaccurate and "lazy" in those systems), where-as the NTK and Denso sensors are ideal, especially on modified engines.

It looks like Ford has been using Bosch sensors for a long time on their products. I also know the "universal" Ford replacement DY1401 is far from "ideal" on these or most other older Fords, yet that is the "OEM" specified universal replacement now. The Bosch 15717 is the original spec'd OEM sensor available today.
 






I will add, without trying to offend, that older Ford ECU programming was known to be quite "faulty" and thus Ford was constantly upgrading the hardware (not just the calibration mind you, but the entire ECU) and even for the Explorer there are multiple ECUs available at this late date that are all configured for the same year engine/chassis/configuration.

I just haven't taken my Explorer into a local Ford dealer and had them do the lookup to determine if there is a newer/better ECU/configuration/calibration for my setup. At least I know that the vehicles all run properly as delivered and is why I was trying to get it to run properly first.

Nothing has been replaced that hasn't needed to be. Either by failure, deterioration or just because of age. Or that I felt was better served by an upgraded part.
 






Well, ended up picking up a pair of Bosch 15717 O2 sensors. Can't hurt to replace them and after 24 years, easy to justify for the $30 I paid for the pair.

I'll have them in on Monday and will swap them out at the next oil change in a few weeks.
 






Well, ended up picking up a pair of Bosch 15717 O2 sensors. Can't hurt to replace them and after 24 years, easy to justify for the $30 I paid for the pair.
DP96XLT - Can you clarify? Previously, you stated that Bosch O2 sensors are "complete s#$%." However, you just purchased two new Bosch sensors. ???
 






I know for fact Bosch O2s are complete ****e on 90s-early 2000s GM PCM systems (very inaccurate and "lazy" in those systems).....
 






Thanks Mbrooks420...

I know Bosch sensors are OEM for most older Fords and the 15717 are spec'd as exactly the same as the original.

Honestly, I could go into the reading process used by the PCM from both and electrical (bias voltage, a/d sampling scheme, etc) to the software side, but all manufacturers spec a specific oxygen sensor and their systems are built around those specs. Sometimes manufacturers get lazy and use an older implementation and you get less than ideal long-term results (or they switch OEM suppliers and end up with a less then ideal replacement).

In those cases it is usually a known issue "in the community" and as such people usually end up figuring out what is the proper replacement or at least know which one ends up being the longest lasting.

For $60 for replacements from Rockauto I would wait until I could tell they were most certainly faulty, but for $30 for a pair, why not replace them.

I will be sure to take some data logs before and after I replace them and do some analysis to see if much has changed. I also have seen brand new o2 sensors be bad out of the box. Rare, but it happens.
 






I've heard really bad things about those Accel coils giving up the ghost after 20k miles or less. I found that out the hard way. The Motorcraft coil is and always will be the best for the SOHC engine.
 






I've heard really bad things about those Accel coils giving up the ghost after 20k miles or less. I found that out the hard way. The Motorcraft coil is and always will be the best for the SOHC engine.

Ditto.
 






Thanks for the info on the Accel coil guys. I will be on the lookout for a Motorcraft one and just pick it up if I can find one for a decent price.

I didn't even consider a Screaming Demon coil for both longevity as well as reports that it is so hot of a coil that it actually damages wires and spark plugs. (To be honest I have seen extremely hot setups damage plugs and eat up distributor caps/rotors and I can't imagine an engine like this needing something that powerful)

Anyone know which OEM makes the Motorcraft coil pack? Denso? NGK?
 






First off I have a 43k mile 1996 Explorer XLT 4dr/4wd with the 4.0l OHV v6 engine. Basically like new, did plugs, wires, PCV valve, air filter, etc.Well, ended up picking up a pair of Bosch 15717 O2 sensors. Can't hurt to replace them and after 24 years, easy to justify for the $30 I paid for the pair.

@DP96XLT

Just asking - After all the new tune up parts, did you:

* Clean your MAF sensor.

*Reset your ECU/Computer so it could re-learn it's parameters for all the new parts?

HTH -
 






MAF sensor is clean and reading properly.

I did reset the PCM. The vehicle is running great now.
 



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^^^^^ Excellent! :chug:
 






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