2.3L ('83-'97) 1997 ranger misfire on bumps

[logan972.3]

Never went to a forum before for help but this problem has persisted and I cannot figure out the root cause. I have a 1997 ranger with a 2.3/5 spd that I recently put a 100k mile replacement engine in. The problem is it consistently misfires/backfires when I hit bumps on dirt roads, smooth roads it runs perfect. The only codes I’m getting are P1121 (which I cannot figure out for the life of me why it won’t go away as I’ve changed both MAF and TPS), O2 sensors which have never had effect on it in the past, and an EGR “a” insufficient flow. I’m not sure if it’s the wiring harness or what but I’d like someone who has more experience than myself to give me some input.

 

[RonD]

Welcome to the forum

Good to post the code with definition just in case you had the wrong definition, lol
P1121 Throttle Position Sensor Inconsistent with Mass Air Flow Sensor

The computer knows what engine it is running, 2.3 liter in this case, so it knows exactly how much air should be coming in at any RPM and throttle position, its just math
What it doesn't know is the WEIGHT of that air, which changes ALOT, from sea level to 5,000ft elevation or from -30degF to 120degF air temp
That's what the MAF sensor is for it "weighs" the air coming in

So the Code is telling driver that the range of MAF sensor, at a specific RPM, doesn't match up with Throttle plate's position

This code could be caused by the stalling out, or the reason for the stalling out
And doing it ONLY when on a bumpy road will be hard to figure out
I assume you have unplugged each of these sensors and checked the wires, and connectors are tight

I would suspect fuel issue first because you have a dual spark system, so electrically spark cutting out on one set of spark plugs shouldn't matter
You could warm up the engine then shut it off, then unplug the 3 wire connector on one of the coil packs
Restart engine and make sure it runs smooth, no misfires
Shut off engine and plug coil pack back in and unplug the other one, same test
If engine doesn't run well on one of the coil packs then you can swap them around and retest, if problem stays with the coil pack replace it
This 2.3l Lima engine ran just fine on 4 spark plugs from 1974 to 1988, the dual plugs give it a bit more power, like the Dodge Hemi dual plug engines


And the Codes you are NOT getting are helpful
There are no fuel pump power codes, so fuel pump relay is OK, but the fuel pump itself or its wiring on the top of the tank may not be OK
And there is the Inertia switch in the cab, it should just popup and cut power to pump until you reset it, but............
As far as you know has the vehicle ever been in an accident?
If so and it was repaired, then inertia switch may not have been replaced and is cutting power to pump on bumps

EEC/PCM Relay, its in the engine fuse box
Swap it with one of the windshield wiper relays, should be same relay part number
Its possible but not likely the PCM relay is opening on a bump, but...............you should get a CEL on/off as computer reboots

 

[logan972.3]

My bad not posting the definition I’m not much of a forum user so this is new to me usually I can figure things out myself but this has got me stumped. I replaced the fuel pump before my last engine blew the head gasket and it never had this issue which is why I kinda believed maybe it’s the wiring harness but wires definitely aren’t my forte. I’ve replaced the coils, wires, plugs, air filter, maf, tps, and fuel filter since this problem first occurred. I’m probably going to look into the relay though because one thing I forgot to mention is the CEL blinks when I hit the bumps but not like your typical misfire blink where it flashes a few times consistently but rather just flickers randomly with every bump. I appreciate your input.

 

[RonD]

The CEL coming on and off at the same time engine stumbles would mean electrical issue for sure, I know DUH, lol

Relays are not expensive, and you can swap windshield wiper/washer relays with EEC/PCM or fuel pump relays on most years and models
Just to take it off the table

 

[logan972.3]

Okay so I was looking under the hood trying to see if there was anything noticeable with the wiring and I noticed the ground to the firewall next to the computer was loose so I tightened that up and it seems to have helped a lot but I still get the slightest stutter and blink of CEL on really harsh ones but the lighter ones don’t seem to be bothering it anymore. I’m going to pick up some relays tomorrow and see what that does but in the meantime you have any clue as to what could be causing it to throw the tps inconsistent with maf/map code?