I recently picked up a 1988 ranger with the 2.9l v6 and I have done plugs, wires, cap and rotor, MAP sensor, cleaned the IAC valve it works properly but I cannot get away from the rough idle and what seems to be a misfire on cylinders 3&6 (the back 2 cylinders). Meaning while the vehicle is running I’ll pull the plug wires one by one and see if it changes how it runs, all cylinders make a change in the idle but when I pull 3&6 plug there is no change, when I ground the plug wire to the block they get spark so the cylinders are getting spark and the plugs are wet so I assume I’m getting fuel. I just can’t figure it out.

on a side note the exhaust smells of fuel, I did and oil change today and the oil was thin and smelled like fuel, and the truck blows blueish white smoke so there is definitely a lot of un burnt fuel going through it.

Im at a loss all help is appreciated thank you!

 

Welcome to the forum

You need to do a compression test
By your own diagnoses you have spark and fuel, only thing left is compression

2.9l runs 9.0:1 ratio so expected static compression is 155-160psi

And have to ask.............3 and 6 are also next to each other on the cap firing order, so very easy to reverse
1 4 2 5 3 6

 

Yeah that’s my next step, my only other thought is that the rear most injector could be stuck on and just completely flooding the cylinders since that injector feeds both 3&6 (to my knowledge). I find it hard to believe that the 2 cylinders in the same position on each side being the only ones without compression. I guess anything can happen though?

 

I'm pretty sure you only have 1 fuel injector for each cylinder.

 

That may be true I guess I just didn’t look hard enough it only looked like there were 3 when I was looking at it from the passenger side? It didn’t seem like there were more on the other side.

haha oops!

 

Did a compression test 130psi on all 6

 

130psi is low but that could just be gauge, 9.0:1 compression ratio would expect 150-160psi but not the point of compression test, its all about averages

So 3 and 6 were not lower than the others so you don't have a compression issue

That leaves spark and fuel
3 and 6 are at the rear of the engine which is where oil from the valve train pools to drain back down to pan, the angle the engine sits at causes oil to pool there
If the spark plugs look oil fouled then could be valve guide seals are bad and intake valve stem is sucking in oil causing misfires
The vacuum in the intake causes oil to be sucked in past intake valve guide seals when valve is closed, so when it opens, air/fuel mix AND some oil goes into the cylinder, which will cause misfire if too much oil is present

 

Another weird thing happened though after I did the compression test I hooked fuel and spark back up. I started the truck and within a few seconds I went around and pulled the 3 plug and I got a change in idle (like it was working!!), pulled 6 and no change but after the truck warmed up for a minute the idle got jumpy again went back and pulled the 3 plug and no idle change so I’m wondering if I have a faulty ignition coil I may replace it and see it’s only $25.

Also could a bad fuel pressure regulator do this? I read to pull the vacuum line to it and check for raw fuel in it and there was, I also had fuel in the brake booster vacuum line when I pulled it a couple days ago.

It could be the FPR because the compression test would’ve cleared all fuel out of the engine and then it ran great for a minute and then was back to rough running and missing....?

Really scratching my head with this, I’ve never had so much trouble from what I thought would be a tune up and a new tank of gas haha

 

Another hunch maybe a bad ICM??

 

Coil and ICM(TFI) would not effect specific cylinders so no, not the problem

YES! on the FPR, its vacuum line comes in at the rear of the upper intake so all that extra fuel would feed 3 and 6 causing rich mix and misfires

Put a towel under FPR and pull off and plug that vacuum hose, see if 3 and 6 start to work again, assuming spark plugs are not fouled

 

Ok I’ll give it a shot!

 

Well the FPR is spraying large amounts of fuel out of the vacuum line when I disconnect it so I think we’ve found a problem?? Haha I guess I’ll replace that and see what happens hopefully this will fix my problems!

 

Yup, that would flood out the rear cylinders

 

FPR it was, running great now as it should considering all the new parts that are plugged into it haha thanks for the help!

 

Good work

Thanks for posting THE FIX

 

Well....... now my fuel pump won’t kick on.

unplugged the (green) relay before doing the compression test and I hooked everything up and now I went to go take the truck for a test drive and no fuel pump.... all connections look good everything is plugged back in no blown fuses, I pushed the inertia switch as well and still nothing.....

just one thing after another.... help appreciated, thanks

 

On the OBD1 vehicles you can manually turn on Fuel Pump Relay(green one) with a jumper wire

Look here: https://www.therangerstation.com/tec...ry/OBD_I.shtml

2nd drawing shows the OBD1 plug-in found in the engine bay, should be on passenger side inner fender in 1988

Find it
On that drawing the Fuel Pump slot is labelled, that slot is the GROUND for the fuel pump relay
With key ON if you ground that slot, fuel pump relay should "click" closed
You can also test that slot for 12v with key ON, it should have 12v from EEC relay(brown base) with key on
(the computers pin 22 grounds the FP relay to activate it, that ground wire runs from pin 22 to this OBD1 slot and out to relay base)

If fuel pump relay clicks closed by grounding then it has 12v from EEC Relay
If fuel pump does not come on then either its fuse or fusible link is bad or one of the fuel pumps is

Not sure if 1988 used a fuse or fusible link for fuel pump

If you pull out the fuel pump relay, and key OFF <<<<
Test each slot in the green base for 12volts, one of the slots should have 12v full time, from the fuse or fusible link, if no 12v then fuse or fusible link is blown

A Fusible link will be connected to Starter Relay(solenoid) post along with battery positive cable, that's where all fusible links connect, just FYI

 

Inertia switch somehow went bad or something, I jumped the wire and the fuel pump turned on just fine and truck started, thanks!

 

Good stuff

 

#1) I always do a Compression check on all engines with a Missfire before working on them.
​​​​​​You might find a bent valve or bad head gasket.