same old, same old. runs rich, sputters, low mpg

[Wrxpulse]

Hello folks,
I've been working on a 1988 ranger stx 2.9 5 speed 4x4 with 260,xxx miles that I bought cheap off a dealership backlot.

It runs ~okay~ but not great, low on torque, and is only getting 14mpg average. While sitting at stop lights it frequently loads up, misses, and smokes black, especially while cold.

I have replaced:
Left head. Had a burned exhaust valve when I bought it. Barely ran.
Oxygen sensor
Idle air
Plugs, wires, cap, and rotor
Installed remanufactured injectors
New high pressure fuel filter, removed mid-filter
New fuel pressure regulator
Ran new engine ground wire, checked ecu grounds.
Retimed to 10 degrees

Fuel pressure shows 40psi key-on engine off, but barely 30 at idle.

Should I replace the high pressure pump? What else should I look for?
Thanks for the help,
-Jack

 

[BlackBII]

Have you checked the compression on all six?

Is there a cylinder in particular that is missing?

Black smoke means its running rich. Was there black smoke before you put in different injectors?

 

[olranger]

if it is running low, then change out the tank pump, i am surprised it will run with that low of pressure

 

[Strieg]

Quick question... Not trying to insult your intelligence or anything, but are you sure the high pressure filter you took off really was a high pressure filter. I thought mine was and bought a new filter and was gonna change it But, when I got under there I realized it was a different shape. So after posting a new thread about it, I found out it wasn't a high pressure filter, it was a high pressure fuel Pump. I only have one filter, and it's a reservoir type. Not inline. But I know later years had both... Just asking because you said pressure was low...

 

[Wrxpulse]

To answer questions in order:

I only checked compression on the left side to confirm the dead hole before changing the head. #1-150psi, #2-145psi, #3-25psi (this was the melted exhaust valve). I did not check the other 3 cylinders because it was about 12 degrees in the driveway that day.

The miss is not localized to one cylinder, it is an "overfueled engine" miss like what you get when cold starting a carburated v8 with a big cam. The miss clears as soon as the engine cleans out the extra fuel.

The black smoke was there before the injectors were changed, they were reman units and appeared identical to the originals (but with less rust)

I'm not convinced its the low pressure tank pump because I'm not seeing fuel pressure drop as RPM's increase at wide open throttle. I taped a fuel pressure gauge onto the windshield and got on the freeway, expecting to see the pressure drop off as the engine wound out. It didnt drop, instead staying at a constant 35ish-psi. If the low pressure pump was failing, I'd expect to see major pressure changes as the high pressure pump drained the filter reservoir the LP pump feeds.

The filter I took out was the paper filter that sits on the inlet of the high pressure pump. This truck does have a high pressure inline filter, but its up near the engine mounts and a PITA to change.

Thanks guys for the replies,

-Jack

 

[CraigK]

Just a coupla thoughts . . .

My B2 runs just fine with running fuel pressure at ~30 psi. (It's higher at idle.)
Although you have replaced the O2 sensor, try disconnecting it to see if this makes a difference.

CraigK

 

[chilsam]

regulater

pull vacum line off reg if gas is present its pumping raw fuel into the intake had a 93 fs bronco that did same thing and that was the problem .Hope this helps

 

[Wrxpulse]

Since the last post I've replaced the MAP, and checked voltages on the air temp sensor, coolant sensor, and TPS. Then I unplugged the o2 and drove it to school and back.

Air and coolant temp checked out okay. TPS showed .96v at idle, so I adjusted it back to .86v. Idle didnt seem as rich, but now it hunts a little sometimes. TPS showed some small "dead spots" with no voltage, so I'll be replacing it as soon as I can.

Unplugging the o2 started a whole different problem. It ran as usual on the way to school, but on the way home the ECU cranked fuel trims full rich and the truck would barely hold speed on the freeway. I've got no idea why it would do this with no o2 feedback, it shouldnt be messing with fuel trims at all.

Wondering if I should replace the ECU, but otherwise running out of ideas.

 

[bobbywalter]

3.7 swap

 

[Earl43P]

Since you have a fuel pressure gage, it should be easy to test the FPR. Hold a steady 2000 rpm, note fuel pressure gage reading. Unplug the vacuum line from the FPR (cover open vacuum line with thumb), note any change in fuel pressure. Do the same test at idle. If fuel pressure change does not occur, you may have a vacuum problem that is showing up in your FPR operation (since you already replaced that part).

http://www.fordfuelinjection.com/index.php?p=41

A vacuum gage might help your diagnosis. http://www.therangerstation.com/Magazine/Summer2003/VacuumLeaks.htm