Extremely Shaky Idle and Also While Driving At Low-ish RPM

[kxri318]

I've got a 1986 Ford Ranger with the 2.9 that I've been fighting to get running right for the past year now and it held an idle, but was kinda rough, misfired, and was all over the place. I decided to swap out the $65 Amazon special fuel injectors for the old oem ones and it seems to run (and shake) a lot more consistently now. It doesn't seem like its misfiring anymore. It does shake a TON at low RPM's though. It shakes the mirror and hood a bit its so bad. It shakes not just at idle, but also when driving up to about 1.5-2k RPM. It also sounds different (and shakes worse) when accelerating. I can't really describe it other than maybe it sounds more bubbly....???? I tried to take a video of the sound but the camera doesn't pick it up too well. One thing to note is that I just reset the ECU by leaving the ground disconnected for a couple hours and I only drove it around the neighborhood for about 5 mins so I don't know if it's fully 'learned' the way its supposed to run, but it didn't get better as I drove it. I would just say it's probably motor mounts since the truck is 37 years old, but it didn't even shake this bad when it ran worse, so I'm not sure.

 

[rusty ol ranger]

I cant tell shit from the videos.,.

The 2.9 is kind of a rough engine...but it shouldnt be shaking things that bad.

Sounds like a missfire to me.

First check fuel pressure at schrader valve (on fuel rail, looks like a tire valve stem)...should be around 40psi

Whens last time it had plugs/wires/cap/rotor?

Lastly...check compression. 2.9s do believe it or not get worn out from time to time.

Also...pull codes on it see if you get anything.

 

[RonD]

Each cylinder needs 3 things to fire
Spark, at the right time
Fuel, in the right mix with air
Compression, above 140psi, and consistent across all cylinders

Of these 3 only one is solely mechanical so can be tested and either ruled out or confirmed as the problem, compression
You can chase your tail on spark and fuel "til the cows come home" but do that AFTER a compression test

Compression test should always be the first stop
Cold engine
Remove all 6 spark plugs first
Test each cylinder and write down results
It will be fairly obvious if one or two cylinders are "not like the others"

The exact numbers are not as important as the difference in the numbers
If 5 cylinder are 120-130psi and one is 90psi then that's the problem
Compression gauges are not calibrated daily, lol, so you are after the differences between majority and single cylinders

Compression does two things
Liquid gasoline can NOT be ignited by a spark, yes, the movie guys take liberties with that one
Compression heats up the gasoline which turns it into a Vapor, and a spark will ignite gasoline Vapor
Compression also has a rebound effect, like winding up a rubber band, the higher the compression the great the rebound

Lower compression in one or two cylinders will cause engine to shake
Each time a cylinder fires it adds power to the crank shaft, so if all cylinders are firing equally, adding the same power, then its smooth
If a cylinder is not firing or firing with lower compression it is not adding equal power to crank shaft and engine will start to shake, the power is "out of balance"
Higher RPMs can hide this imbalance but its still there

 

[kxri318]

I cant tell shit from the videos.,.

The 2.9 is kind of a rough engine...but it shouldnt be shaking things that bad.

Sounds like a missfire to me.

First check fuel pressure at schrader valve (on fuel rail, looks like a tire valve stem)...should be around 40psi

Whens last time it had plugs/wires/cap/rotor?

Lastly...check compression. 2.9s do believe it or not get worn out from time to time.

Also...pull codes on it see if you get anything.

Each cylinder needs 3 things to fire
Spark, at the right time
Fuel, in the right mix with air
Compression, above 140psi, and consistent across all cylinders

Of these 3 only one is solely mechanical so can be tested and either ruled out or confirmed as the problem, compression
You can chase your tail on spark and fuel "til the cows come home" but do that AFTER a compression test

Compression test should always be the first stop
Cold engine
Remove all 6 spark plugs first
Test each cylinder and write down results
It will be fairly obvious if one or two cylinders are "not like the others"

The exact numbers are not as important as the difference in the numbers
If 5 cylinder are 120-130psi and one is 90psi then that's the problem
Compression gauges are not calibrated daily, lol, so you are after the differences between majority and single cylinders

Compression does two things
Liquid gasoline can NOT be ignited by a spark, yes, the movie guys take liberties with that one
Compression heats up the gasoline which turns it into a Vapor, and a spark will ignite gasoline Vapor
Compression also has a rebound effect, like winding up a rubber band, the higher the compression the great the rebound

Lower compression in one or two cylinders will cause engine to shake
Each time a cylinder fires it adds power to the crank shaft, so if all cylinders are firing equally, adding the same power, then its smooth
If a cylinder is not firing or firing with lower compression it is not adding equal power to crank shaft and engine will start to shake, the power is "out of balance"
Higher RPMs can hide this imbalance but its still there

When I listen closer, I can hear it stumbling a bit at what seems like random times.


Fuel pressure was about 34 psi when I tested it if I remember right. I know it was from 30-40.

It's had two different brands of plugs within the last 2k miles to see if that made a difference (It didn't)
Wires are still OEM I believe.

Cap is brand new, rotor is not. I think the rotor is the OEM one, but not 100% sure.

Compression:
Cyl 1: 137.5
Cyl 2: 140
Cyl 3: 145
Cyl 4: 135
Cyl 5: 147.5
Cyl 6: 145

KOEO test didnt give any codes, supposedly passed all of them
KOER test gave codes 12, 33, 25, and 74

12 - idle out of range high (Weird considering It's idling around 750 rpm I think which is what it's supposed to be at according to the sticker on the radiator support)
33 - EGR Valve fault/not closing properly (Replaced EGR valve and EGR vacuum solenoid about a year ago with Standard Motor Product ones)
25 - Knock not sensed during dynamic response test (don't know what this means)
74 - Brake on/off switch fault, not activated (don't know what this means)

While running the test it randomly blipped the throttle a little which was weird. I tried running the cylinder balance test, but I followed the instructions in my scanner booklet and nothing happened. It said to give it full throttle for a second then it would enter the cylinder balance mode test and take up to 5 mins. I let it idle for 5 mins, nothing about how it ran differed and nothing happened on the scanner.

I want to note that a couple months or so ago, I changed the ECU to one from an 86 Bronco Automatic and it ran great for about a day after putting it in, then went back to running like it used to and never ran as good as that again. It also seemed to have to relearn every time I shut the truck off. It would run weird for about 30 secs when starting it after shut down during the day it ran great.

 

[rusty ol ranger]

Compression looks good.

If your wires are original...change them...and run motorcraft plugs.

Change the rotor too.

I think idles supposed to be 650 IIRC.

Dont worry about the knock sensor code and the brake code.

Sounds like possibly a bad EGR vacuum solenoid...its over on passenger side fender...follow the red and green plastic vacuum lines from the upper plenium over to it.

EDIT...nevermind you replaced that...

Did you replace the EGR pulse sensor? The little black box by the EGR valve?

 

[kxri318]

Compression looks good.

If your wires are original...change them...and run motorcraft plugs.

Change the rotor too.

I think idles supposed to be 650 IIRC.

Dont worry about the knock sensor code and the brake code.

Sounds like possibly a bad EGR vacuum solenoid...its over on passenger side fender...follow the red and green plastic vacuum lines from the upper plenium over to it.

EDIT...nevermind you replaced that...

Did you replace the EGR pulse sensor? The little black box by the EGR valve?

I'll look into getting new wires and a rotor soon.

I checked the idle rpm when hot and its 700 in park if my tach is right. The sticker on the radiator support says 800 for a v6 auto, but it says that in neutral.

If the EGR pulse sensor you're talking about is the DPFE sensor, then yeah thats new too. Don't remember what brand that was though, can't find it in my purchase history either.

 

[rusty ol ranger]

I'll look into getting new wires and a rotor soon.

I checked the idle rpm when hot and its 700 in park if my tach is right. The sticker on the radiator support says 800 for a v6 auto, but it says that in neutral.

If the EGR pulse sensor you're talking about is the DPFE sensor, then yeah thats new too. Don't remember what brand that was though, can't find it in my purchase history either.

Yeah the little black box on the plenium by the EGR.

How did the EGR port look inside the plenium? I had EGR codes after replacing everything too and the port was completly blocked by rock hard carbon. I had to chisel it out with a bolt

 

[kxri318]

Yeah the little black box on the plenium by the EGR.

How did the EGR port look inside the plenium? I had EGR codes after replacing everything too and the port was completly blocked by rock hard carbon. I had to chisel it out with a bolt

Sorry for taking so long to reply. I didn't have much time to do anything with the truck. I finally put in the new rotor and plug wires and it changed nothing. The EGR port has a small lining of carbon about 1/16" thick. Does that seem like a big problem...? The truck was running stupid rich not too long ago (still runs a bit rich now but not nearly as bad) so not sure if maybe all that gunked up the EGR. I forgot to mention in the original post, but it surges at startup for a good 30 seconds then stops surging. It didn't surge like this with the amazon injectors.

 

[rusty ol ranger]

Sorry for taking so long to reply. I didn't have much time to do anything with the truck. I finally put in the new rotor and plug wires and it changed nothing. The EGR port has a small lining of carbon about 1/16" thick. Does that seem like a big problem...? The truck was running stupid rich not too long ago (still runs a bit rich now but not nearly as bad) so not sure if maybe all that gunked up the EGR. I forgot to mention in the original post, but it surges at startup for a good 30 seconds then stops surging. It didn't surge like this with the amazon injectors.

View attachment 96397

Thats not nearly as bad as mine was but id clean it and clean the egr while youre at it

 

[Cees Klumper]

Have you checked the fuel pressure regulator on the fuel rail? If it leaks fuel the mixture will be way off. Also, there could be a vacuum leak, these engines really need all vacuum lines to be just right, also in terms of where they are connected (before throttle body and after on the intake manifold). Ignition timing/spout connector set right/connected? There's so many things that can go wrong but once sorted, these engines run very well and smooth.

 

[kxri318]

Have you checked the fuel pressure regulator on the fuel rail? If it leaks fuel the mixture will be way off. Also, there could be a vacuum leak, these engines really need all vacuum lines to be just right, also in terms of where they are connected (before throttle body and after on the intake manifold). Ignition timing/spout connector set right/connected? There's so many things that can go wrong but once sorted, these engines run very well and smooth.

Yeah, fuel pressure was 30-40 psi with no leaks. I tested for vacuum leaks a while ago and took care of the ones I could see, haven't tested since. Timing was set with the spout connector out and to 11 degrees.

Pretty sure I found the issue though, I got the oem injectors out and went to clean them again and found out that one of the solenoids just isn't doing anything when I put power to it. They all worked a couple months ago so that's weird.