Rough Idle :(

[GluttonforGloom]

New here, looking for some help with an 89 2.6 5sp MM I bought. So, I've recently changed the oil, spark plugs, and plug wires but the truck has been idling pretty rough. I've got some semi old gas in the tank but I threw in some cleaner and it sounded a little better after letting it cycle through. Now, I'm thinking it's the fuel pressure regulator but I have no clue where it is, how I'd for sure diagnose it, and where I could get the right one. Any help or advice would be great. I'm partially new to getting hands on but I'm not scared to so let me know!

[xboxrox]

My truck 1986 Dodge Power Ram50 2.6L

Things I've done to improve idle & fix slight engine miss:
Replaced PCV valve
Set ignition timing @ 9°BTDC
Cleaned EGR port in intake manifold

Things planned to do:
Remove test inspect EGR valve
Adjust idle air/fuel mixture screw on Mikuni carb
Ajust & set idle RPM to factory specs
Replace Coolant Temperature Sensor (hope it fixes gauge & it's not a wiring problem)

NOTE: Not sure if the CTS is cause for rich running; could be..!

Welcome here & good luck fixing your truck
George

[FMS88]

New here, looking for some help with an 89 2.6 5sp MM I bought. So, I've recently changed the oil, spark plugs, and plug wires but the truck has been idling pretty rough. I've got some semi old gas in the tank but I threw in some cleaner and it sounded a little better after letting it cycle through. Now, I'm thinking it's the fuel pressure regulator but I have no clue where it is, how I'd for sure diagnose it, and where I could get the right one. Any help or advice would be great. I'm partially new to getting hands on but I'm not scared to so let me know!

Welcome to the forum. If the truck is completely stock, it won’t have a fuel regulator. Does it have any modifications? Is the carburetor the original Mikuni or does it now have a Weber?

[GluttonforGloom]

My truck 1986 Dodge Power Ram50 2.6L

Things I've done to improve idle & fix slight engine miss:
Replaced PCV valve
Set ignition timing @ 9°BTDC
Cleaned EGR port in intake manifold

Things planned to do:
Remove test inspect EGR valve
Adjust idle air/fuel mixture screw on Mikuni carb
Ajust & set idle RPM to factory specs
Replace Coolant Temperature Sensor (hope it fixes gauge & it's not a wiring problem)

NOTE: Not sure if the CTS is cause for rich running; could be..!

Welcome here & good luck fixing your truck
George


Thanks for the info! I'll take a look at the pcv valve and try changing it out. I've no clue how to adjust ignition timing or either of the fuel and air mixture but I'll youtube what I can and go from there.

[GluttonforGloom]

Welcome to the forum. If the truck is completely stock, it won’t have a fuel regulator. Does it have any modifications? Is the carburetor the original Mikuni or does it now have a Weber?


Thanks! The truck is completely stock and it just has the stock Mikuni carb. It looks a little rough so I had bought a rebuilt kit I've yet the get thrown on.

[FMS88]

Thanks! The truck is completely stock and it just has the stock Mikuni carb. It looks a little rough so I had bought a rebuilt kit I've yet the get thrown on.

The Mikuni is a bear to rebuild; many small parts like springs, plugs, check balls, o-rings, diaphragms, etc. some of which are not included in the rebuild kit. A Weber (if legal) or an aftermarket rebuild are easier options. But if you go for it, separate the three major parts (air horn/float chamber cover, the plastic mixing body and the throttle body) first, then disassemble each separately to manage better all the small parts. Layout the parts on a big table and take lots of pictures to help the reassembly. Also, ignore the exploded diagram included with the kit; it's for a different carb model. You need one for a 32-35 DIDEF-435MT carb (87-89). The FSM has a pretty good diagram and steps to disassemble and reassemble. If you need more info, just specify in a post.

[GluttonforGloom]

If I were to do the swap for the weber, which one would I need? Would it still pass smog here in Cali? Is it relatively easy to change it out and would I need to add anything? Would it solve my rough idle issue?

[FMS88]

If I were to do the swap for the weber, which one would I need? Would it still pass smog here in Cali? Is it relatively easy to change it out and would I need to add anything? Would it solve my rough idle issue?

Look at these threads about which Weber to get, what's needed additionally and what the installation involves:
http://www.mightyram50.net/vbulletin/showthread.php/8869-Weber-swap
http://www.mightyram50.net/vbulletin/showthread.php/9104-Looking-fr-genuine-webber-carb-kit
http://www.mightyram50.net/vbulletin/showthread.php/210-Weber-32-36

There are many other threads and posts concerning the Weber, so search the site. There's a wealth of information available to answer all your selection and installation questions.

Will it solve the rough idle issue? It should IF the problem is due to the Mikuni. It very well could be especially if the Mikuni is original, but all other possible causes (electrical, fuel delivery, compression, etc.) should to be checked and eliminated so you don't risk replacing the Mikuni because of some other fault.

I don't know the Cali emission rules so I can't say for certain if the Weber could pass the smog tests. That's a question for your local DMV and other California members who have considered or made the conversion.

[SubGothius]

I don't know the Cali emission rules so I can't say for certain if the Weber could pass the smog tests. That's a question for your local DMV and other California members who have considered or made the conversion.

The Weber should pass a tailpipe sniffer test when properly tuned/jetted, but obvs. it would fail a visual inspection requiring all original-type equipment, not sure if that's required everywhere in Cali or just the major metros.

[geezer101]

The Weber won't pass inspection in Cali. The Mikuni is a biatch to pull apart for the uninitiated - if you've never pulled down a carb, either this is the perfect place or possibly one of the worst (if you can strip and rebuild this thing and get the truck to run afterwards, you are well on the way to becoming a Mikuni master...) Main points of failure - accelerator pump diaphragm (easy to diagnose and relatively easy to replace even with the carb still mounted), secondary vacuum solenoid (again easy to diagnose but requires a little force to remove it from it's mount - not part of a kit as it's a large vacuum actuator), choke release assist diaphram (you'd never know if it's failed without visual inspection, causes internal vacuum leak - not part of a rebuild kit and there are 2 or 3 types of diaphragms with different actuator rods staked to them) and the biggie - water pellet choke assembly. Obvious when it fails (lots of greasy thick wax on the throttle shafts/linkages) does not come part of a kit, the wax pellet is used on Suzuki Sierra/Samurai and is obsolete/almost impossible to find and equally impossible to install. Some Mikunis have a 'rivetted' housing preventing the choke from being accessed, but the heads can be ground off the anti tamper screws and the threaded shafts backed out and replaced with regular metric screws. If you are going to do it, clean it thoroughly before removing it from the manifold, drain some coolant, take pics of everything then undo the nuts and hoses etc. Have an uncluttered work space with a tray so when you take the top housing off the fuel bowl/carb you don't lose the ball bearing and brass floats in the fuel supply gallery (you lose these - game over...) Do NOT mess with the adjuster screws on the throttle linkages. Once you start messing with these, your idle and choke will suffer.

[FMS88]

The Weber should pass a tailpipe sniffer test when properly tuned/jetted, but obvs. it would fail a visual inspection requiring all original-type equipment, not sure if that's required everywhere in Cali or just the major metros.

https://glendalesmogchecktest.com/smog-check-services/dmv-smog-check-information/

This web-page about Cali smog testing lists the 40 of 58 counties that require testing. Unfortunately for GluttonforGloom it includes Kern County of which Bakersfield is the county seat.

[xboxrox]

Hi Glutton,
You could buy a reman carb from https://www.carbtech.us/automotive.html or get a 2nd Mikuni from Pick n Pull (extra parts on the cheap) and rebuild it yourself ~ checkout my photo albums ~ if I did it then you can do it

[FMS88]

GlutonforGloom - The rough idle could be due to a vacuum leak. With the many lines for the feedback carb, their age and the SoCal heat, it's a possibility. Inspect them and brake booster line for cracks or breaks or use the propane method to check for leaks as described here:

https://www.thedrive.com/maintenance-repair/40028/how-to-check-for-vacuum-leaks

If you remove any lines, suspect that a PO has messed with them or want to confirm their routing, Post #2 of this thread has a good diagram of the hoses and their connections.

http://www.mightyram50.net/vbulletin/showthread.php/8147-1988-mighty-max-carburetor-vacuum-diagram-needed(actual-photos)?highlight=vacuum+diagram

[xboxrox]

O2 sensor ?

[GluttonforGloom]

Sooo, I changed 90% of the tubing and it fixed the mostly fixed the rough idle but every time I press the gas from a stand still, it wants to die. Still the carb? Going to take it to try and get smogged tomorrow so maybe it'll pass. Any advice is always appreciated because I'm getting ready to sell this thing ):

[xboxrox]

Carb accelerator pump squirts gas ?
Catalytic converter not plugged ?
O2 sensors - coolant temp sensors ok ?
Fuel pump is ok ?
Fuel & Air filters ok ?
Ignition timing is ok ?
Intake Exhaust Carb fasteners all tight (none missing) ?
Ground wires tight & not disconnected or missing ?
Read last two posts on this (rough idle) thread: http://www.mightyram50.net/vbulletin/showthread.php/9061-94-4G64-idle-issues?p=83005#post83005

Best wishes on the fix & sale :thumbup:

[FMS88]

Test the accelerator pump. If it coughs and sputters when the throttle is opened quickly but not when opened gradually, the circuit is suspect. With the air cleaner top removed, look down into the carb throat while opening the throttle (engine off). If you don’t see a downward stream of fuel, the circuit is plugged or the diaphragm broken.
The carb kit includes the pump diaphragm and gasket that can be replaced without removing the carb. There’s more to the circuit but trying a new diaphragm is a good start.

[GluttonforGloom]

Well guys, all the help was appreciated but one thing lead to another and with all the issues I found wrong with the engine, I learned I need a whole new one. Will make a whole new post so it stays on topic and I'll post a link.

[xboxrox]

Glutton my truck was doing the same damn thing ~ it turned out to be a leaking carburetor float ~ the heavy float would sink and cause flooding killing the engine ~ am curious how you decided a complete new engine is the FIX ??

My truck runs pretty good/great now BUT not until the following was done:
- New cylinder head
- Rebuilt Mikuni carburetor (DIY)
- Removing a 100% plugged catalytic converter
- Replacing eng coolant temp sensors (both) and O2 sensor
- Fixing vacuum leaks
- Replaced distributor vacuum advance diaphragm
- Replacing PCV & air filters (all 3)
- Setting ignition timing (initial mech & vacuum advances)
- Cleaning & testing EGR and passages in the intake manifold
- All the usuals plug wires coil NGK5BPS or whatever spark plugs your eng requires
- Setting idle RPM

------------------
Stuff never done yet:
- Set idle RPM by adjusting carb air/fuel mixture screw
- Leak test every vacuum hose & connection
- Replace any cracked/brittle/split ended vacuum hoses (leaking or not)
- Much more but my old brain is quiting for now

-----------------

YouTube has a video of a guy buying a complete G54B long block to bolt his new cylinder head onto ~ his sources saved him a ton of money ~ maybe I saved the link, will check...
HERE IS THE LINK: https://youtu.be/KEWsEmip8UU

? Why must the entire engine be replaced ? (knocking sounds/no compression/cracked block...)

Respects ~ George

[GluttonforGloom]

Much appreciated! So, the conclusion was due to the amount of issues I had found wrong with the engine. My timing is off a bit, I'm pretty sure I've got a burnt valve and I have rod knock very, very badly. I sound like the worst train chugging along when at medium/high rpms. I say all this while not having the most or best mechanical pov so bear with me! A few coworkers helped me identify the issues but sometime soon I'll post a video of it revving and let you all give me some feedback. I'm very close to selling it since I need a daily but I am fighting and holding out to keep it so any advice is appreciated!