Erratic idle and wont rev up very well at all

[Flatbedder81]

Hello all. I have a 1988 ford ranger xlt 4x4 with auto trans and 2.9 v6. It has devoloped a condition that has me stumped. It starts up pretty easily, but will quickly start idling very erratic. And is very hard to Rev up as the idle cuts out the whole way up the rpm band. Here is a list of everything I have done to the truck so far

-new o2 sensor
-new iac valve
-new intake air charge temp sensor
-new coolant temp sensor
-I rebuilt the distributor with new hall effect sensor, rotor and cap and retimed to 10 btdc
-new plugs and wires
-new ignition module
-new coil pack
-refurbished injectors
-new Delphi in tank fuel pump and sender
-new fpr
-new fuel filter
-new ecm

I have a new Delphi high pressure in line fuel pump on the way. This problem is driving me crazy and I am tired of throwing parts at it. Could this be a fuel problem? Any help is appreciated

 

[Shran]

Have you taken a fuel pressure reading? Sure could be fuel related. My F150 did this years ago, would run OK at idle but would cut out and sputter anywhere past that, especially under load. It was a weak high pressure fuel pump. Very odd problem, 99% of the fuel pump failures I've seen result in a pump that is just stone dead.

Might be worth taking a compression test too, just to rule out a burnt valve, cracked head, etc.

 

[Flatbedder81]

I did do a key on engine off check and got a low reading, like 29-30 psi so that is why I ordered the new in line pump. Hopefully this is my issue. This is a very nice truck that I bought from an old man that had sat for almost 15 years with very little to no use and is near mint. So I would like for it to run as good as it looks! And this has been a gradual issue, started as a small miss here and there and has developed into it being un driveable at this point. I haven't done a compression check, but it sound pretty good cranking, so I'm pretty sure I don't have a dead cylinder. But I reckon I should try and do one.

 

[Dirtman]

The problem with those trucks that sit forever with little use is that pretty much all the rubber dry rots. Seals, gaskets, hoses etc. Having a weak pump wouldn't surprise me if it say dry.

 

[ecgreen]

Could be a vacuum leak no? My first 2.9 ran that way and I found the one of the unused ports on the UIM didn't have a cap.

 

[Flatbedder81]

The hoses all look good and I used an unlit propane torch around all the normal leak spots and couldn't find a leak.

 

[ecgreen]

Hopefully it's that pump. Let us know for when (not if) this happens to me

 

[Shran]

Try taking a fuel pressure reading while it's running, should be around 30psi at idle and will come up to 40 briefly when you crack the throttle open (low vacuum scenario.) Low reading indicates a supply issue, high indicates FPR problem but you replaced that.

Any codes present? CEL does not necessarily need to be illuminated in these trucks for codes to be present

 

[Flatbedder81]

Okay....went ahead and replaced HP fuel pump. Cleaned all grounds again. Took the alternator wire harness completely off and inspected and wrapped with new electrical tape reinstalled. STILL having the same problem. It will mot Rev past 2k without throwing a huge fit, cutting out and almost sounding like I'm losing all electrical power. Tried using a brand new battery, no change. It will idle just fine, and it runs perfect with the alternator unplugged. It has a brand new alternator with new regulator. I had it tested at autozone and tested good. And I've tested it, it is putting out 14.4 volts at idle.

 

[Flatbedder81]

Also...bought a scan tool, no codes. Getting an 11 every time

 

[Paulos]

If the truck sat for a while I would suspect the injectors and fuel system in general. Are you sure the refurbished injectors are working right? I once had a refurbished injector that would occasionally stick open. And refurbished only means cleaned (to varying degrees) and new o-rings (for the most part).
Also, are you certain you got the injector wiring harness connected to the right injectors on cylinders 2 & 5? Cylinders 1, 4, and 2 are on bank 1, and cylinders 5, 3, and 6 are on bank 2.

 

[Flatbedder81]

If it were the injectors, then why would it run perfect with alternator unplugged?

 

[Dirtman]

Injectors are powered by electricity?

 

[Shran]

I wonder if you could watch the voltage at say, the coil? while you rev up the engine with the alternator plugged in. Sure sounds to me like it's feeding back into something. Running on just battery power would stabilize the voltage to everything.

This reminds me of a bad alternator I had in my Explorer. I actually had it rebuilt right before a big trip I went on just because it had a ton of miles on it... I had a weird problem with my headlights and dash lights flickering if the engine was under a significant load. Ended up being a bad voltage regulator. They only caught it when the shop hooked it up to their oscilloscope and saw a tiny fluctuation.

 

[Paulos]

I guess I didn't read the part about it running perfect with the alternator disconnected . Well, at least that narrows it down to an electrical problem. Have you checked the connectors that are on the drivers side inner wheel well. The insulation on the wires there have a tendency to shrink and have been known to cause problems.
Have you tested the voltage output of the alternator as you're attempting to rev it (at least 1800 rpm)? Also, when you check the voltage, check for AC voltage. If you have any AC voltage it's the alternator. I just read that a shorted diode in the alternator will introduce AC voltage. Real bad for your electronics, and not necessarily detectable when testing the alternator at your local auto parts store. It's too bad you don't have an old spare alternator to try a swap.