88 ranger 2.9L Inconsisent Stumble maintaining 75mph

[BillRod]

Hi All

1988 Ranger 2.9L 5spdMitsubishi, 4x4, Manual Tcase and hubs, ext cab, at least 175K miles, owned about 6 months.
Last week I cut off the stupid 1foot long cherry bomb and replaced with an oem style muffler to quiet it down, and new air filter. I pulled the left front spark plug and it looked great so I put it back in without replacing any of them.
Fuel filter is only a few months old.

Around town it runs great. no complaints at all.
Until this week it would run great anywhere, any speed.
Last spring the previous owner went from Colorado to Branson Missouri and back with no issues.

The Problem that started this week is maintaining 75mph on the hiway using only part throttle it will sometimes feel like it is stumbling.

I can get on the hiway and run 5 or 6 miles at 65 with no issues in either 4th or 5th and it runs great. When I get out of town and the speed limit goes up to 75 I can easily accelerate to 75 but when I back off the throttle to maintain 75 is when it sometimes will feel like it is stumbling.
This stumble occurs at in either 4th or 5th gear.

Another odd symptom is sometimes when I go down the hiway and it starts stumbling I exit to simply turn around and the return trip at 75 may or may not stumble. Turning around like this I do not stop the truck or turn it off or anything, I simply get off and back on again, sometimes it runs great and sometimes it stumbles.

I have ran Gumout injector cleaner through 2 tanks but it does not seem to change the symptom.
Very inconsistent, been wrenching for many years and this is a new issue for me.
I was thinking of replacing the fuel filter again just to see.

I did look through the Chiltons troubleshooting setions but this is not covered anywhere.

Anyone have any thoughts or advice on this?

Thanks in advance.
Bill

 

[johndeeregarner]

I think I know what you are talking about. I have a 86 with a manual in it and they sometimes does that when you're going at a faster speed. I'm not sure how to explain it but its kinda like a slack that you get with most older manuals. If you are going 50-55 in 4th gear (that is if your tranny is the same as mine) and you let off the gas then you will kinda feel the tranny slow you down, due to it going to fast for the gearing. I think that is what you are feeling. My truck does this only at certain speeds in certain gears, 75 may be yours. This shouldn't be a big concern. You may check the U joints on the drive shaft just in case.
Hope this helps,
jdg

 

[BillRod]

Hi JohnDeeregarner

Thanks for the reply but I really don't think it is the tranny.
I have the mitsubishi 5 speed stick.

When the stumbling occurs the engine rpm will start to fall, I can watch it falling on the tach.
When it's not stumbling I can cruise at 75 without issue and the rpm will stay constant.
The inconsistency and the engine speed falling are the main reasons why I don't think it's the tranny.

There's some sort of intermittent fuel or electrical issue causing it to lose power at part throttle at high speed.

Fuel filters are cheap so today I'll try replacing that again and see how that impacts things.

Anyone else have any other thoughts or Ideas?
I'm open for any suggestions.

Thanks again
Bill

 

[AllanD]

a similar symptom can be generated by a Throttle position sensor with a "Dead spot"

it should be noted that ded spots on the TPS's internal potentiometer occour most often where the throttle is kept in "Cruise position" for the most time.

near fixed position with slight variations.

IOW if tyou and the previous owner cruised at the same speed
(and 75mph across Kansas with a 3.73 geared 2.9 is as typical as it gets) then that's where your dead spot would likely develop.

AD

 

[BillRod]

Hi Allan

Replaced the Throttle position sensor but it did not help.
Still have the same issue.

Any other thoughts?
Thanks
Bill

 

[Cyberbeer]

A shot in the dark but maybe check the fuel pressure regulator.

 

[Cyberbeer]

What was the temperature outside? Here is something I came across while browsing my alldata.

Article No. 89-3-4

SPEED CONTROL - COAST AND ACCELERATION MODES - ABNORMAL OPERATION IN HIGH AMBIENT TEMPERATURES
FORD: 1986-89 ALL

LINCOLN-MERCURY: 1986-89 ALL
LIGHT TRUCK: 1986-89 ALL

ISSUE: Abnormal speed control operation in the coast and acceleration modes may be caused by loss of electrical contact between the steering wheel slip rings and brush assembly. This condition usually occurs in high ambient temperatures when the steering wheel slip rings and brush assembly are warm.

ACTION: Improve the electrical continuity of the steering wheel slip rings and brush assembly by applying a new service released grease on the contact area. Refer to the following procedure for service details.

1. Remove the steering wheel, Refer to the appropriate Car or Light Truck Shop Manual for service details.

2. Clean the old grease from the steering wheel slip rings and brush assembly contact areas.

3. Apply the new service released grease, (E8AZ-19590-A), on the steering wheel slip rings and brush assembly contact surfaces. This new grease can be identified by its bright orange/red color.

4. Reinstall steering wheel.

PART NUMBER PART NAME CLASS

E8AZ-19590-A Grease B

OTHER APPLICABLE ARTICLES: None
WARRANTY STATUS: Eligible Under Basic Warranty Coverage
OPERATION: 890304A
TIME: 0.4 Hr.
DLR. CODING: Basic Part No. 9C899
Condition Code: 53
OASIS CODES: 2900

EDIT: My bad, guess this only refers to cruise control

 

[1987rangerxlt]

Cyberdeer!

They moved my tail light message to http://www.therangerstation.com/forums/showthread.php?p=373662#post373662.

Please check it out because I had a post about the turn turn signal switch that you might be able to provide some input to.

 

[BillRod]

I went out this morning and bought an OBD1 code reader, 21.99 at checker.
I ran the KOEO test, the stored memory test and the KOER test.
All came back as clean. No error codes at all.

So I guess I need to start looking at the fuel delivery system.
I'll post that in a new thread.

Thanks again for all the ideas and help.
Bill

 

[IMenriched]

You might be wise to double check the ground wires on this beast.

have you ever been behind a trailer at night that the tail lights flicker going down the road...generally this happens because of a poor connection and or ground.

well the same happens to these older electronic ignitions...only instead of lights flickering its the ignition going on and off....OK ..off the soap box

 

[CraigK]

Try disconnecting the O2 sensor at the end of the Y-pipe.

Also, when you did all this work recently, did you put anything into/through your fuel system that was not gasoline? The Gumout came after the problem was first noticed? Any cleaners etc. before that? (That might have damaged the O2 sensor.)

CraigK

 

[Cyberbeer]

Sorry for resurrecting an older post but I may have found the solution to this problem. About 3 months ago I pulled out my dead motor and swapped in an 88 or 89. Fast forward to a month ago I swapped my 87 TB and took off the smaller one.

About 3 days ago I noticed it kinda stumbling while holding speed above 50, sometimes it would sometimes it wouldn't. Today I took a look where the throttle cable clips on, and the assembly that ties that to the TB. Anyway, it had a good 3/4 inch of play going forward and at least 1/2 inch of play moving side to side. In my theory with such light pressure on the throttle to hold the speed stead the whole piece was wiggling and jumping around.

Either that or the TPS was just going bad I dunno which, but swapping the 88-89 TB back on fixed the problem.

 

[cocoasranger]

A shot in the dark but maybe check the fuel pressure regulator.

I had this problem for years on my wifes 87 Taurus. After it got progressively worse I took it to the dealer who quoted me $1500 to fix.Took it home and drilled out the aluminum plug in the fuel pressure regulator and turned the Allen screw a quarter turn at a time till it ran best. Has been running like a race car for 5 years since then. Not sure if the Ranger regulator is adjustable.

On my Taurus, if it started to stumble, you could let off on the gas for 10 seconds or so and it would return to normal when you hit the gas again.

 

[BillRod]

Try disconnecting the O2 sensor at the end of the Y-pipe.

Also, when you did all this work recently, did you put anything into/through your fuel system that was not gasoline? The Gumout came after the problem was first noticed? Any cleaners etc. before that? (That might have damaged the O2 sensor.)

CraigK

Nothing ran through the fuels system right before the problem started.
I have used gumout a couple of times since I bought it with no issues until now.

If the O2 sensor is bad or damaged wouldn't that show up as an engine code when using the OBD1 tester?

I bought one from Checker and it showed No error codes at all not even in memory.
Every test came out as 11, which means it passes with no error codes.

Thanks
Bill

 

[CraigK]

Bill

Probably won't show a code.
It will take you all of two minutes to go underneath your truck, locate the O2 sensor and disconnect it.
Then drive it.
If there is no change, waste another whole two minutes (okay, maybe three) to reconnect it.
Try it.
Or not.