88 ranger 2.9L Inconsisent Stumble maintaining 75mph

[BillRod]

I'll try the O2 sensor once tomorrow's snow passes.

Today I hooked up the Fuel pressure gauge and drove it on the highway.
Driving in town pressure was about 30 at idle to about 39 or 40 under hard acceleration.

I was a bit surprised because I thought electric fuel pumps put out consistent pressure but this acted like a mechanical pump and increased with engine rpm. I guess that's how these are supposed to work.

Anywho... on the highway the pressure moved between 32 and 40 or so, depending on whether I was accelerating or maintaining 75.
It took almost 30 miles on the highway at 75 mph before the stumbling issue started.
When it started to stumble I had to put my foot in it the keep it running.
Pressure was almost 40 with my foot in it, but I did notice that it did not drop much when I took my foot out of it to slow down.
The fuel pressure regulator is only a year or so old as the previous owner replaced then.

Is it possible the regulator is bad and there's too much pressure and that's what is causing it to stumble?

Does this sound like a possibility?

Thanks
Bill

 

[Tedybear]

Regulator sounds fine. About the only other test would be to pull the vacuum line off from it and check for fuel. (they get cracks in the rubber and leak inside the regulator) The regulator works via engine vacuum. Lower the vacuum? The higher the fuel pressure. Higher the vacuum? The pressure should be about 30-35ish...with about 40 being the top off point at low/no vacuum. (lower vacuum=engine under load or accel and more pressure is needed. Higher vacuum=engine not under load, thus less pressure needed)

The pump does put out 'full pressure' at all times, the regulator just kicks it down and adjusts it as needed.

TPS would have been my first guess. (mines got a dead spot and it surges at idle and it's acting up surging when I run constant speed of about 30mph)

O2 sensor is possible, it's recommended to replace it every 60,000 miles. It's a heated O2 sensor, and over time it is prone to failing...MAP sensor...partly clogged injectors...etc..

Could be any number of things...but I'd recommend the basics and give it a full ignition tune up. (checking one plug won't tell the entire story.) Cap/Rotor/wires/plugs...If nothing else? It's good maintenance to get out of the way.

S-

 

[cocoasranger]

OK, here's a dumb question. Did you hook up the fuel pressure gauge before or after the fuel pressure regulator. If before, then it would not show the regulator cutting pressure too much when the stumbling happened if the regulator is faulty.

 

[BillRod]

So this is what I've done/checked so far.

Electircal stuff so far:
-TPS is brand new, Replaced that first as suggested here.
-I pulled all 6 plugs, all looked very good and consistent.
-Plug wires are pretty new and in great shape, ohmed out consistent with eachother.
-Check engine light not on, but used an OBD1. testing the KOEO and KOER tests as well as searching for stored memory codes and the OBD1 confirmed no error codes during tests or in memory.


Fuel delivery so far:
-Replaced fuel filter again. (did it when I bought it and again after I did the electrical checks above).
-Fuel pressure guage hooked to the fuel rail schrader valve after the regulator.
-Checked the fuel delivery using a pressure gauge as detailed in the Chiltons and all checked out ok.
-Chiltons suggested driving with pressure guage hooked to check for pressure under load. Did this by adding 1x2 wood blocks between the hood and hinges raising the back of the hood to allow gauge hose to fit through.
Got the results posted before, all seemed ok except the pressure seemed to remain close to 40 during stumbling.

Mechanical:
-Checked for vacuum leaks using a propane torch, Unlit, around every vacuum line and fitting I could find.
-Checked for play in the throttlebody and there does not appear to be any excess play.
-Gumout was ran through when I first bought 6 month's ago and also before and after the stumbling started, did not seem to affect the issue.


Recap:
-I have not tried disconnecting the O2 yet as CraigK suggested. Just started snowing again.

-It seems to happen mostly on flat hiway maintaining 75, But as soon as you leave the hiway it seems to run fine in town.
-I did notice it a little though yesterday after climbing a long very steep hill in town climbing in 3rd gear using a lot of pedal, when I got to the top and was on a flat road it stumbled some until I got to the office just a little over a mile from the top of the hill. got back in after lunch and ran fine.

-Does not backfire at all so the Timing chain is probably ok.

With all the diagnostics - OBD1 and Fuel pressure gauge - checking out ok I am Kinda getting stumped

Any other thoughts or ideas?

Thanks
Bill

 

[fastpakr]

You can check the O2 sensor directly with a volt meter. Unhook it from the harness, then clip the meter leads in so you're measuring voltage between the sensor ground and the signal return. Look for the voltage to exceed .5 volts as you run the engine (especially if you snap the throttle open quickly so it tries to enrich the mixture, like a carb would with an accelerator pump). If it never goes above .5 volts (or, as in my case, does absolutely nothing), you can condemn the sensor immediately.

 

[BillRod]

You can check the O2 sensor directly with a volt meter. Unhook it from the harness, then clip the meter leads in so you're measuring voltage between the sensor ground and the signal return. Look for the voltage to exceed .5 volts as you run the engine (especially if you snap the throttle open quickly so it tries to enrich the mixture, like a carb would with an accelerator pump). If it never goes above .5 volts (or, as in my case, does absolutely nothing), you can condemn the sensor immediately.

I'll try that.
Just to clarify, the Signal Return is the engine side of the wire connection, right?

Thanks
Bill

 

[fastpakr]

You want to be probing the O2 sensor harness, not the end that leads back to the ECM. I'm not sure which wires are which on your O2 sensor (or even whether you have 1,2,3, or 4 wire sensor). You'll have to check a wiring diagram for that. The test is the same, you just need to ensure you're probing the right wires.

 

[BillRod]

Ok, I jacked it up and crawled under and I've got a 3 wire O2 sensor.
One black wire and 2 White wires.
There does not appear to be any visual color difference between the 2 white wires.

Looking at the Chilton's wiring diagram it appears to state the following:
-BLK wire going to what appears to be a large ground bus.
-GRY/YEL wire that goes to the ignition switch.
-BLK/LT GRN wire that appears to go to the EEC POWER RELAY.
-A second, unlabeled wire that also goes to the ground bus. This unlabeled wire makes 4 wires, Maybe this 4th unlabeled wire is just the connection from the threads of the O2 sensor to the exhaust pipe?

This BLK/LT GRN wire also seems to be connected to ground with a dot on the schematic. Maybe that is just the way the diagram looks in the book? Idunno, sure looks like a solder dot in the diagram...

Getting back to the 3 wires on the sensor, Since 2 are just plain white how do I tell which is which?

Will it hurt anything if I put a digital meter across from ground to the wrong white wire?

Thanks.
Bill

 

[fastpakr]

You'll have to look at the wires going into the other half of the connector to see what wire pins to what on the sensor - sounds like you have a generic aftermarket sensor that doesn't match the factory wiring colors. Measure from the blk/lt grn to blk.

 

[BillRod]

Doh!!!
Didn't think about the colors matching on the other side of the connector...

It's snowing like crazy out there but this is Colorado so it'll probably nice and sunny tomorrow after work.

Thanks again.
Bill

 

[BillRod]

OK So I pulled the connector and stripped back some of the big plastic cover around the 3 wires and they appear to be as follows;

Black with red stripe
Blue with White stripe
Brown with no visible stripe.
These color combos do not match the colors in the book.

Two of these had a piece of light green tape around each of them but that's all. I assume each should have had 2 pieces of colored tape to make the colors match the diagram?

So... without the colors to match the diagram (although someone here probly could have deciphered the actual wire colors) And since it was mentioned here that the recommended replacement for the O2 sensor should be 60K miles I just decided to spend the $39 at Autozone and replace it.

Took it for a 75 mile round trip on the hiway and it ran great!!!
Stumbling did not occur at all, and I think is used less fuel from the previous trip that was less miles!!!

Thanks Fastpakr and everyone else for the help on this.

Now I can move onto the tiny antifreeze leak at the front of the engine under the thermostat.
It's either the water pump gasket or timing chain gasket.

Thanks again
Bill