94 ranger 4.0 having major issues

[Cchapa020]

Hello I’m having issues with my 94 ranger 2wd 4.0 ohv. The issue I’m having is the truck starts right up then revs up to almost 2000 then drops to about 4-500 then revs up again then bogs out and dies or continues this cycle. I have recently done the head gaskets and entire cooling system. I just can’t wrap my head around what’s going on with it

any help is greatly appreciated, thanks.

 

[Uncle Gump]

I would start by checking for vacuum leaks.

 

[89Twincharge]

^ definite vacuum leak, with truck running listen for hissing in engine bay. Tha iac can malfunction and do wierd stuff but it's usually constant high or constant low rpm

 

[CrashDS]

I'd say I vacuum leak also. I had the same issue with my 99 Mazda b2500. It's pretty easy to find the vacuum leak bye taking a can of starting fluid and spraying it around your hoses an intake when your vehicle is idling. Your vehicle will sputter when starting fluid Is sucked in through the leak.

 

[Uncle Gump]

I'd say I vacuum leak also. I had the same issue with my 99 Mazda b2500. It's pretty easy to find the vacuum leak bye taking a can of starting fluid and spraying it around your hoses an intake when your vehicle is idling. Your vehicle will sputter when starting fluid Is sucked in through the leak.

I would be very careful with starting fluid. In fact I say don't try that. It's way to volatile... one spark and the engine compart goes up in smoke.

I prefer propane... just use a torch head and regulate the gas flow pretty low and move the unlit torch head around suspect areas. You will notice a change in RPM's when you found the leak.

You can also google smoke test for vacuum leak. Very effective and zero chance of undesired flames.

 

[Cchapa020]

Thanks guys I will check for leaks in a couple hours and let y’all know what happens

 

[RonD]

I would pull out the computer and open it up and change the 3 blue capacitors just to do it, but one or two will most likely be leaking

Had to do my 1994 4.0l last July because of running issue I couldn't pin down
Runs better now than 2 years previous, just odd issues as the caps fail

Yours does read like an air leak but the capacitors are do to be changed in any case, 20+ years are about the limit
Under $5 in parts, just need to solder in the new ones
If you can't do it then any radio/electronics repair shop can

 

[Cchapa020]

I’ll look into that and yeah damn near everything on this truck is stock and the last owner wasn’t the greatest on maintenance hell I went to change the fuel filter a will back and the damn guy installed it backwards

 

[Cchapa020]

So I looked for vacuum leaks couldn’t find one only hissing I can hear is coming from throttle body

I did a koer test and got these codes
172: oxygen sensor lean
136: oxygen sensor fault always lean
538: insufficient rpm change during koer test

the only thing I can think of is the cam synchro when I did the head gasket I replaced it and couldn’t figure out if it was 10*
26* or tdc where you install it so installed at tdc and lined up the reluctor with the center vane in the window I also replaced all injectors

 

[Cchapa020]

I also cleaned iac valve and that helped a bit but not much

 

[RonD]

Have all my original sensors on my 1994 4.0l with over 400k now
Only new O2 sensors every 10-12 years, because they do wear out, only sensor that does have a time limit

Codes do show lean on left and right so not O2 related would have to be dirty MAF sensor or an upper intake vacuum leak
Wouldn't be cam sensor related
Check PCV Valve and hose, also power brake booster hose

Ignore code 538 its a test code

 

[Cchapa020]

I’m leaning toward the pcv valve I have a fair amount of oil buildup and crud in the intake upper and lower I will check that valve here in a bit

 

[Cchapa020]

Okay the pcv valve hose is fine no cracks no leaks same with the brake booster hose

here’s what the pcv valve looks like

 

[Cchapa020]

Okay I just got a new set of intake gaskets let’s hope these do the trick

 

[Cchapa020]

Update I installed the upper and lower intake gaskets and she runs way better it’s actually drivable now thank you guys for your help it’s much appreciated