1994 Ranger Bogs with any throttle input

[mississippi305]

Hi All,

Have a new to me 1994 4.0 Ranger.

I’ve driven it ~15 miles. For 14 of those it ran fine. But at a stop light, I accelerated and you could feel all the power disappear and it now bogs at any throttle application.

In the video you can see that it will idle fine, but touch the gas and it immediately bogs and misfires.

I’ve changed fuel filter made no change. Unplugged MAF, also no change. I wouldn’t think it’s a worn spark plug/wire issue since it happened so immediately and that it idles fine.

Thought about a clogged cat, but it has plenty if pressure coming through tail pipe.

Any help you can provide is much appreciated!!


https://youtube.com/shorts/OTsRMDrrNss?si=3wJSCLjeOvQE-Iqr

 

[rusty ol ranger]

Id about wager on a TPS

 

[Shran]

Clean the MAF sensor first
Second check for any holes in the air intake tube between the throttle body & MAF. Notorious for that.
Third, check your TPS sensor voltage, best to do this with an analog multimeter so you can watch for dead spots - but you can do it with a digital one. Should be at 0.75v-1v at close throttle, and move steadily towards 5v at full throttle with no dead/weak spots. Do this with the key in Run, engine off
Fourth, fuel pressure check, should read around 35psi at idle and around 40 if you blip the throttle

 

[mississippi305]

Clean the MAF sensor first
Second check for any holes in the air intake tube between the throttle body & MAF. Notorious for that.
Third, check your TPS sensor voltage, best to do this with an analog multimeter so you can watch for dead spots - but you can do it with a digital one. Should be at 0.75v-1v at close throttle, and move steadily towards 5v at full throttle with no dead/weak spots. Do this with the key in Run, engine off
Fourth, fuel pressure check, should read around 35psi at idle and around 40 if you blip the throttle

TPS only sweeps to about 2.8V. Will grab one this afternoon and see

 

[Shran]

TPS only sweeps to about 2.8V. Will grab one this afternoon and see

Before you spend money on parts check the reference signal voltage too - there are three wires at that sensor - ground, +5v reference and the variable one that you tested. If you only get 2.8v at the reference wire then you have a different problem. Should see 5v there at all times. Probably a bad TPS though.

Just out of curiosity in your video, did you have the throttle pegged wide open? Will the RPMs rise smoother if you just ease into the throttle?

My old beater Explorer has a weak fuel pump, it will spit and sputter and pop back through the intake or just die if I don't let it warm up for a few minutes. Similar to your problem. I just use it to push junk around the yard so replacing the pump has not been high on my priority list to fix.

 

[mississippi305]

Before you spend money on parts check the reference signal voltage too - there are three wires at that sensor - ground, +5v reference and the variable one that you tested. If you only get 2.8v at the reference wire then you have a different problem. Should see 5v there at all times. Probably a bad TPS though.

Just out of curiosity in your video, did you have the throttle pegged wide open? Will the RPMs rise smoother if you just ease into the throttle?

My old beater Explorer has a weak fuel pump, it will spit and sputter and pop back through the intake or just die if I don't let it warm up for a few minutes. Similar to your problem. I just use it to push junk around the yard so replacing the pump has not been high on my priority list to fix.

well well….reference wire only sees about 2.3V as well. *sigh*

and it sputters no matter the amount of throttle input.

 

[mississippi305]

Clean the MAF sensor first
Second check for any holes in the air intake tube between the throttle body & MAF. Notorious for that.
Third, check your TPS sensor voltage, best to do this with an analog multimeter so you can watch for dead spots - but you can do it with a digital one. Should be at 0.75v-1v at close throttle, and move steadily towards 5v at full throttle with no dead/weak spots. Do this with the key in Run, engine off
Fourth, fuel pressure check, should read around 35psi at idle and around 40 if you blip the throttle

Replied below, but not sure if you get notifications. But checked the reference line, and it’s only seeing about 2.3V as well. Is that controlled by the ECM?

 

[Shran]

Replied below, but not sure if you get notifications. But checked the reference line, and it’s only seeing about 2.3V as well. Is that controlled by the ECM?

I don't recall, it might be. That reference wire is shared with a bunch of other sensors too as is the ground. They all report signal voltage back to the ECM for sure.

I would start by cleaning up all the grounds under the hood and in the cab. It might just be a shorted or dirty ground. There is one directly below the brake master cylinder on the frame that I've seen broken off and is easy to miss. Check voltage at some other sensors - coolant temp or air charge are in that area and will for sure share the same common power & ground, see if it's just a problem with the TPS or if they all read low.

If you can rule that out, you might pull the ECM and open it up & look at the capacitors inside, there are a couple of them. They can fail by popping open on the top or blowing a little plastic piece out the bottom & leaking electrolyte. If those fail they can cause weird issues.

 

[mississippi305]

I don't recall, it might be. That reference wire is shared with a bunch of other sensors too as is the ground. They all report signal voltage back to the ECM for sure.

I would start by cleaning up all the grounds under the hood and in the cab. It might just be a shorted or dirty ground. There is one directly below the brake master cylinder on the frame that I've seen broken off and is easy to miss. Check voltage at some other sensors - coolant temp or air charge are in that area and will for sure share the same common power & ground, see if it's just a problem with the TPS or if they all read low.

If you can rule that out, you might pull the ECM and open it up & look at the capacitors inside, there are a couple of them. They can fail by popping open on the top or blowing a little plastic piece out the bottom & leaking electrolyte. If those fail they can cause weird issues.

I now remember why I hate pre OBD2 vehicles

Checked the aur charge sensor, 5v. And the. Just to triple check the TPS, tested it again, and this time had 5v reference and swept from 1.0-4.8v.

Makes no sense, but it is what it is.

 

[gaz]

@mississippi305 ,
Check all vacuum hoses, battery cables/connections and engine bay grounds.

 

[Shran]

I now remember why I hate pre OBD2 vehicles

Checked the aur charge sensor, 5v. And the. Just to triple check the TPS, tested it again, and this time had 5v reference and swept from 1.0-4.8v.

Makes no sense, but it is what it is.

Haha, does it run better now, something loose, did your meter probe short out on something?

I like pre OBD2 vehicles because the CEL only comes on if there is a fairly serious issue and even then sometimes it doesn't, and it's not dependent on moon cycles to turn off...

 

[RobbieD]

And it may have been oxidized or corroded terminals in the TPS connector itself. Especially if you unplugged, and plugged it back in and the engine running conditions improved.

I run only OBD1 trucks; I think of it as a "smart points and carburetor" system.

 

[rusty ol ranger]

Haha, does it run better now, something loose, did your meter probe short out on something?

I like pre OBD2 vehicles because the CEL only comes on if there is a fairly serious issue and even then sometimes it doesn't, and it's not dependent on moon cycles to turn off...

Thats what i like about OBDI....no engine lights unless youre going to be walking in a few miles

 

[RobbieD]

Thats what i like about OBDI....no engine lights unless youre going to be walking in a few miles

Yep. Instead of CHECK ENGINE the OBD1 red light should say PRAY.