Engine/Transmission (1994 - 1998) slight rough idle

[XJSuperman]

I've asked this over on DTR and wanted to get some opinions here as well. I'm sure there are those of us who visit both boards like me.



Any way I have a '95 2wd dually with automatic trans. 283K miles. I bought it about 8 months ago.



I've tabbed the KDP, put in a new lift pump (cleaned the screen too), and put in boost/egt/and trans temp gauges. The truck had the trans rebuilt buy a reputable shop about 6 months before I bought it and it's definitely better than stock.



Since I've owned it it has had somewhat of a rough idle. It's not enough to say it's a miss but it's noticeable even from out side the truck. Not audible really (not to me anyway) but if you touch the truck you can feel it shaking.



About the only thing I have not done is a valve adjustment but I can't see them being that bad to cause this.



It accelerates not problem. No smoke at start up or when driving (unless it the 'appropriate' time for it to). Feels as though it has the power it should for a stock 160HP motor. I've pulled a 29' travel trailer with it with no trouble and have had over a ton of weight in the bed and it ran fine.



I'm getting reasonable mileage... about 16 MPG in town with some idle time. It gets better with less idle time and I've seen close to 18MPG on the one tank where half was hwy mileage and half in town with idling... but have not put a full tank through it onthe hwy.



Per some advice from a friend with a '95 I recently increased the idle speed which seemed to help a little... but it's still got the shakes... however it does start a lot faster now even though it wasn't real slow to start anyway. I put the new lift pump on prior to that but it made no difference either.



I have also replaced the overflow valve... no change.



So I am leaning towards injectors. I've read several folks threads on how theirs lasted 500K... others say they replaced theirs at or before 200K. I am also thinking of 'upgrading' with a 50HP injector since they seem to be the same price or close to it as stock replacements... so why not right? I'm not looking for a hot rod since I know even with a good transmission I'm not able (nor do I care to) add 300 HP to the truck... but a tad more wouldn't be a bad thing.



I've looked at DDP, TST, Southern Diesel extreme, Piers and probably a lot of others. All seem to be within $100 of each other and they all seem to have a good rep (of course at the moment Southern Diesel's site won't work for me).



So a some questions now that you know my life story.



1) is there any other possible thing I shold be looking at before putting in injectors. If something else could be wrong that will be less $$ I'd rather do that

2) Are there manufacturers out there I should steer clear of?

3) Should I go ahead and run a boost elbow if I go with 50HP injectors? I don't plan on messing with the fuel plate.

 

[budnate]

adjust the valves, you will see rough idle if there loose and tight.....

 

[surfbeetle]

adjust the valves, you will see rough idle if there loose and tight.....

I agree, this was going to be my first suggestion. There's really no point in troubleshooting anything else until you know that your valves are set properly. The next suggestion is going to be that you may need to either clean or replace your injectors. Also as for your idle speed, it should be set on a 12 valve to 750-800 rpm with the AC on.

 

[JR]

Does it feel rough at all rpms or just at idle? At nearly 300k it would be a good idea to inspect the damper. Not saying this is your issue, you would more than likely feel this at higher rpms than idle, but would still be a good idea to get your eyes on it and make sure its in sound condition. A bad damper will give an engine more of a vibration through the rpm range than a miss, sometimes hard to distinguish the two... by some of what your describing it may be worth looking into.

 

[XJSuperman]

My idle runs between 850-900 in gear with the AC on. it only does this at idle. Riding down the road the only thing you hear/feel is the road and whatever else squeaks and rattles on the truck... motor is smooth at higher RPM's.

I replaced my dampener with a brand new one a couple months ago when I tabbed the KDP. I replaced the belt too.

I know I need to do the valves even if just for peace of mind. I'm lazy though... I've had the valve cover gaskets and bolt o-rings for several weeks now... just haven't taken the time to pop the covers off and do the job.

 

[XJSuperman]

Adjusted the valves this afternoon and just returned from a test drive. didn't make much difference despite having a few valves out of spec. Does seem to be a tad more peppy and it 'hits the wall' a a bit higher thanit used to. Before at 2200 RPM it stopped fueling... or at least it felt like it. Now it seems to go to 2300 or a bit higher.



It's just such a slight thing and the trucks runs so good. Should I wait and see if it gets worse?

 

[GAmes]

Those early p-pumps are increasingly be reported as failing internally, I believe from sticking plungers. Does it only idle rough after it has warmed up? If so, try pouring cold water over the pump and see if the engine smooths out (yes, I am serious). IIRC, LNaugle has stated he uses Stanadyne to overcome the sticking pump in his '96. It wouldn't hurt to try, and additive is a lot less expensive than a p-pump.



edit; Some gov spring adjustment, or installing after market gov springs will move that defueling rpm above 2200. My pump defuels at about 3300 rpm with the stock springs, but it was set up on a test stand at a performance shop.

 

[XJSuperman]

The roughness is there from initial startup. Doesn't matter if it's cold, hot, or somewhere in between. It's been very steady like this since I bought the truck. It's never gotten worse... or really any better for that matter. I'm beginning to wonder if it's just signs of the truck itself showing some age. It certainly saw some use and abuse before I got ahold of it... maybe it's just going to shake a little? LOL

I need to find someone with more experience than me to ride in/drive it for me... again this is a slight 'lope' and it may be nothing (God willing).

I know I can tweak the GS or put in aftermarket ones... but I was told by TST I shouldn't unless I add a fuel plate as the truck wouldn't run right with a stock plate and a 3K (or higher) GSK.

I'm trying to keep the truck stock as long as possible. And even if/when I do BOMB it I'm looking at 25-50 HP injectors and a #10 plate at most. It's not a rocket at all but I don't want/need it to be.

 

[BDaugherty]

to piggyback onto this thread, which injectors would be best for a small gain with best fuel economy on a 160 hp 12valve? i have a customer with a 95 model taht has 240k and a slight miss. i think it may be in the pump, but was leaning towards a set of factory 215 injectors to either fix the miss or compliment the upcoming pump repair. if i do the pump, it will get a 3k gov spring for sure, but what would be the mildest fuel plate that would work well with the gov spring and 215 inj? powere goals have already been met just by moving the stock plate forward and tweaking the afc, just looking for better running and a little more hp up top.

after looking back at what i wrote, i probably should have started a new thread but it just takes too long to type on my phone so i will just leave it and risk the backlash.

 

[XJSuperman]

HIJACKER! LOL... being the thread starter I'm not worried at all... ask away. it may help me too.

 

[GAmes]

Concerning the GSK. I currently have a totally stock, unmolested p-pump mounted on my engine. It does not defuel until about 3100 rpm. Adjusting your springs could make you engine smoother, I believe, and would move the defuel point up. You said you increased the idle speed. With the engine and trans at normal operating temp, in Drive, A/C on it should be about 850.



The Bosch shop in Austin will pop test stock 12 valve injectors for free. You might check around and see if a shop near you offers the same service. In a week or two I'll be installing a rebuild engine into my truck complete with new 215s. I wouldn't mind loaning you the ones I have in my current engine if you want to try a set.



I believe the hijacker (sorry BD, couldn't resist) needs to evaluate the turbo and the trans on his customers truck before installing bigger injectors. Plate profile would depend on how the truck is used. I really liked my #11 until I had a custom towing plate installed.