1999 Ford Ranger 2.5 only runs with ECT unplugged

elementaltoad · Nov 16, 2014

I just got a 2.5 Ranger from a friend of mine who was tired of trying to figure out what went wrong.

I've had it for 2 days so I still have some tests I'll need to do, but I have gone ahead and started replacing maintenance items and other bits that look beyond their useful service life.

Here is what I've noted so far:

Truck only runs with the engine coolant temperature sensor unplugged (this is the ECU sensor).

I'm assuming this puts the truck into limp/open loop?

-Vacuum is good (Gauge tested)
-IAC replaced
-New battery
-New air filter (previous owner installed)
-New timing belt (previous owner installed)
-New clutch (previous owner installed)
-New fuel pump and filter (previous owner installed)
-MAF cleaned and tested good
-ECT sender and sensor replaced, voltage and Ohms are good
-Fuel pump relay, ECM relay, and Inertia switch tested and good
-Fuel pressure is there, but I need to grab a gauge to put on it tomorrow

I can get the truck running with the ECT unplugged, but it runs rough and seems to end up bogging and stalling randomly. (the gas is old so this may be part of that particular issue.

My main question is what it does to the truck that causes it to run with the ECT unplugged. With it plugged in the truck will try to crank but never fires up.

Anyone familiar with these trucks dealt with this or know what to look for? This is only my second Ford, and first Ranger.

Thanks!

Earl43P · Nov 17, 2014

ECT Pin 38 PCM
IAC Pin 39 PCM
They share their power source with a few other items, from a splice group. This should NOT be suspect since you state that voltage to the ECT was good. By good, I assume you mean 5 volts, which should all be fed from PCM Pin 90 (reference voltage).

DPFE
TPS
etc.

The ECT acts like a choke in that it richens the fuel/air ratio for cold starts. The PCM does this in conjunction with the IAT by lengthening the duration of the fuel injectors' open time.

Just throwing a WAG out there, since yours WON'T start with the ECT connected, let's assume its fuel mixture isn't RICH enough....meaning it's very LEAN. Lean condition can be caused by large vacuum leaks, such as the intake tube isn't connected from the throttle body to the airbox, the PCV system tubing has a bad connection, or the brake booster hose. Lets ignore the smaller vacuum leaks that are also possible, like the fuel tank vent system feed, the EGR system and the IAC, which you've replaced and the tubing to the HVAC vacuum reservoir under the airbox.

That's what I'd concentrate on and rule out, after you get fresh fuel in it.
Let us know if you want to pump all the old fuel out, there is an easy way to do that with the fuel filter disconnected, simply disconnect the Inertia switch and run 12v straight from B+ to one of its connector pins. Only one of the pins will make the fuel pump run, no worries if you touch 12v to the wrong pin first, Pump just won't run.

Should you want the schematics for your truck, send me a PM (private message) and include your email address.

Welcome to The Ranger Station!

elementaltoad · Nov 18, 2014

You are correct about being too lean at start up, and it indeed will not run well or rev when it actually decides to turn over. I went to harbor freight and got their "all-in-one" fuel pressure tester kit since they were sold out of the basic kit.

Recap:
-15psi when priming
-Immediate pressure drop off, after 2-3 second prime
-Pressure while running 20psi MAX

I also grabbed a quick disconnect kit to pull the fuel filter, I'm going to replace that tomorrow night and see if the fuel pump is good and can be salvaged. It was replaced by the previous owner not very long ago. Hopefully it's simply a clogged filter. He stopped driving the truck when he bought a new one, sitting and being ran rarely probably did little favor for the fuel system.

I'll report back once I determine what is up with the fuel system, I appreciate your help greatly! If I do drain the fuel, what can you do with stale fuel? It appeared to have about 10 gallons of old fuel in it when it was dropped off at my house via flatbed.

Earl43P · Nov 18, 2014

Personally, I'd wait until you fix the fuel pressure issue. Then I'd top it off with 93 and DRIVE IT.

I'm going to guess your fuel pump assembly is the culprit. I think that 99's had the fuel pressure regulator and fuel pump all in the same assembly, in the tank. Might be pricy.

I did have a new fuel pump fail in a 93 that I flipped for $. The new owner found that the rubber tube that came with the new fuel pump had chemically reacted to the fuel and melted/failed. The new pump that I installed was still good, he simply replaced the short piece of hose. Perhaps YOU will get that lucky!

http://goldwingdocs.com/forum/viewtopic.php?f=15&t=14679

Simply add water to it, shake it, let it settle, drain off the water, then put a gallon or so of the old gas in your truck. Repeat until all the old gas is gone.

elementaltoad · Nov 18, 2014

Unfortunately it looks like you are right. I put a good fuel filter on, the old one was definitely clogged and the pressure stays a bit better while running, but it still maxes at about 30psi.

And it doesn't look like they sell the regulator separately, Rock auto has decent prices on the whole assembly so I may grab one of those and just replaced the whole god forsaken thing. I'll take the bed off, it sounds like that is the easiest route, especially now that the tank is full of fuel.

Hopefully I can get that done this weekend and perhaps have the thing driving. Thanks again for your quick and informational replies, it really helps! This little truck is way too nice and useful to let it go to pot due to a seemingly simple issue.

Earl43P · Nov 19, 2014

If you are working alone, the bed doesn't have to come completely off.
All you really need is some clearance, Clarence. Prop up the front of the bed. There will be a lot of dirt on top of the tank, I pressure wash that before opening it up.

Use a long breaker bar with the T55 bit (buy several). Start spraying penetrant on the bed bolt threads from underneath DAYS prior.

One tailight connector lives at the rear center of the bed.
3 little screws by the filler cap.
Be gentle with the tank electrical plug, and clean it up!
Fun times.

elementaltoad · Nov 20, 2014

Sounds easy enough. Regardless it can't be as bad as lifting the bed on my Dodge 2500 by myself with a 5th wheel hacked in there by the previous owner!

I got the truck cleaned up tonight, such a pretty truck. It was left sitting at my buddy's house for a good long while, mold all over it and a bed full of trash and leaves. I love the color, some sort of sunset orange metallic/amber color.

I'll let you know how tomorrow goes, I'm going to try and get the bed to slide back, I've got a couple of saw horses I can set the back on. I don't have a replacement assembly yet, but he did say he already replaced it once.

My hope is that the hose inside is missing a clamp and popped off. I will upload some pics tomorrow. I may even see if I can improve the assembly to make it more hardy. Are there any typical DIY upgrades for these? I know most of these OE style units are lacking quite a bit.

elementaltoad · Nov 20, 2014

Bed is off, 15 minute job including looking for the tow straps I used to tie down the bed after I set it on top of the tires. Good call on that! Much easier than having to drop a tank, and now I get to be OCD and clean the stuff that never sees daylight!

elementaltoad · Nov 20, 2014

Got the pump out when it wasn't raining. I have an odd question. I keep reading that the fuel pressure regulator is in the tank. My pump doesn't have one, it also appears to have blown the hose off the pump outlet. Are the older pumps interchangeable?!

I'm going to at least fix the hose and see if the truck runs right with actual fuel pressure, but I thought it was odd for a 1999 built on 9/11/98 to be missing a regulator in the tank.

elementaltoad · Nov 20, 2014

Well, on second though, in 1999 they went returnless, I am assuming because my truck was built in 1998 it was equipped as a 1998. And on second look, my truck does appear to have all factory connections and a return line on the end of the fuel rail behind/under the intake. I'm going to run to the store to get a better fuel hose.

If someone can chime in before I put it back together I will double check back here, but as of now it looks like I was misleading myself by believing the truck was a "built in 1999 truck".

elementaltoad · Nov 21, 2014

Looks like I've got it figured out, I got a free hose from autozone that fits better and put twp hose clamps on each end. Truck is up and running like a champ. Oil change tomorrow and some more driving.

Can't beat a free fix!

Thanks again for all the help Earl, and now I know to get parts for a '98 when I need them heh.

1999 Ford Ranger 2.5 only runs with ECT unplugged

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