Stumbling 2.9L

[The Fox]

Hello everyone, just had a question that I would like to have answered.

Here goes, my truck has the 2.9L with a strange problem. It runs just fine and starts perfectly, but at idle it stumbles and shakes a lot. It has a constant RPM of 1000 at idle when warm, but it shake around without the engine RPM dropping. It also does it when I hold the throttle with the clutch depressed just a little faster and less violent.

It has had new wires, plugs, cap and rotor less the 1000 miles ago, it also has a new fuel filter/air filter at the same time. I also have the problem that it will rhythmically rev up and down until it either dies or recovers with a bump up in RPM and runs normally. I got it to work better when I and my auto teacher in high school (I bough the truck from him) cleaned the throttle body while the engine was running with cleaner, but it has gone back to the way it was.

The truck has 150,000 miles on it. My auto teacher replaced the heads with aftermarket ones at 107,000 miles 12 years ago because someone who brought it to his shop and sold it to him because of the work. He owned an engine shop and took the motor out and rebuilt it, honed the cylinders, new pistons, clean it all up and the link and drove it for those 12 years as a shop truck to move engines around.

Let me know of any thing else you would like to know. I also appreciate the help.
Thanks
Nick

 

[ranger]

someone can correct me but have you replaced the injectors or ran any injector cleaner throught it they could posibly be clogged

 

[low_five]

sounds like a cylinder isnt firing good to me.

did you change the spark plugs or wires recently?

 

[The Fox]

I changed the plugs and wires, cap and rotor, fuel filter and air filter 4 months ago, but I did not drive it for about a month after doing it.

I have fun cleaner through it and it go just a little better.
Nick

 

[low_five]

what you should do is start it and let it idle. start pulling one plug wire at a time and observe the motor. it will stumble badly everytime you pull one out but its no big deal. pull one, watch the motor, and put it back in.

go to the next plug, pull it, watch the motor, etc. eventually you will find one that doesnt change the motor much when you pull it out. thats your bad cylinder. shut the engine off, pull that plug and look at it. describe the condition of that plug for us to read.

 

[The Fox]

I shall try it, I am just not sure that is what it is. It feels too soft for a misfire.
Nick

 

[The Fox]

Just something that I would like to ask, what size vacuum lines does the 2.9L uses? I am going replace them(some are hard and others are showing signs of wear). I am going to try the old propane trick next week when I get a new bottle of it.

I did try to do the plug test, all did the same thing.
Nick

 

[IMenriched]

yes check for vacuum leaks carefully...don't forget about the brake booster or CC if equipt.

also double check grounds and connections

 

[welton]

Sounds similer to a problem I'm having. Mine has a slight miss at idle, but cuts out badly when driving. I replaced plugs,wires, distributor cap and button, fuel and air filters but no help, then I noticed that my coil seems to be "SPARKING" or grounding out, (you can only see this at night). I replaced the coil but the problem must be elsewhere. Does this seem like your problem? Anyone have any Ideas?

 

[The Fox]

I am thinking it is a vacuum leak, but I am going to go get a spool of the lines if anyone knows the dia. of the hose.
Nick

 

[IMenriched]

On mine I noticed a minor one on the molded elbow on the back side of the FPR. IF i pushed on it slightly it would be more noticable.

not saying that where your is at...just a place to look
Also to point out that there is many different sizes of vacuum line...one size isn't going ot cover all souces.

 

[da_blake]

I Just got done dealing with this same problem, complete rebuild engine, but failed to clean injectors. Pulled injectors, cleaned all injectors and fuel rail. now runs like a dream.

 

[The Fox]

I know that it is a fuel problem as the last time I pulled codes, I got a low fuel pressure code. But it is quite pricey to get that work done properly. I have not done a fuel pressure test as of yet, but that is being added to my weekend project. How do you clean injectors when they are removed?

I pulled a vacuum line off the running engine, almost no change in RPM or sound. I assume this means vacuum leak somewhere. I am going to go get a spool of 5/8" and 1/8" vacuum hose this weekend and try and change most if not all of them.
Nick

 

[Psychopete]

I know that it is a fuel problem as the last time I pulled codes, I got a low fuel pressure code. But it is quite pricey to get that work done properly. I have not done a fuel pressure test as of yet, but that is being added to my weekend project. How do you clean injectors when they are removed?

The computer looks for unexpected voltages and incomplete circuits in the self test. It's pretty common that codes never point to anything in specific. Eg, o2 lean code; not only could the o2 be shot, but more than likely something else is causing the engine to run lean or misfire.

With that being said, there (although I wish there were) is no sensor that monitors the fuel pressure. I don't believe there is a fuel pump monitor circuit on that '88, but I could be mistaken. That just monitors 12 volts that are actually running to the fuel pump. What was the actual code you received?

Fuel pressure test is simple (not really a project ), and is really the only way to see problems with fuel pressure.

People have soaked them in fuel injector cleaner, then opened the solenoids, and blow through the injector backwards with low amounts of compressed air. Also replace pentle caps and o-rings. Use valsoline on o-rings when reinstalling injectors. For some reason, I am thinking that the pentle caps weren't so easy to find, but got some from Napa. Keep in mind that it's a Universal part not specific only to 1988 Rangers.

If it were me, I'd take them in to a shop to clean/check or buy new ones. I REALLY hate dealing with the fuel rail. I have flow matched from Rouge Performance that were realitively inexpensive compared to buying all new. They'll more than likely end up in my Tempo if they cross over, my 2.9L is getting replaced soon.

Pete

 

[lunghd]

On mine I noticed a minor one on the molded elbow on the back side of the FPR. IF i pushed on it slightly it would be more noticable.

not saying that where your is at...just a place to look
Also to point out that there is many different sizes of vacuum line...one size isn't going ot cover all souces.

Same issue here - stumbling at idle. Seems to run fine on the road. Didn't check for vacuum leak... found gas leaking from regulator.