Just bought a 90 Jimmy 6.2 diesel. Great body for an eastern vehicle it's age. I plan to run it on biodiesel, but that's certainly some ways off. I know very little about diesels and for now would appreciate troubleshooting advice for these 3 issues:
1. horrible fuel consumption (15 mi/gal)
2. sluggish power: I've experienced very short bursts of power when first started - really takes off - then returns to being a slug. Can get to highway speeds eventually, but struggles on inclines.
3. Vibration (and humming) above 50.
I'm aware these have a known harmonic balancer (my new word of the day) problem, but can I just assume that's where the vibration comes from or should I test for other culprits (wheel bearing and/or drive shaft come to mind)?
As for the mileage and performance I'm going to hazard a guess they're related?
These trucks are not powerhouses.
The burst of speed when the engine is cold is cold advance which helps the engine get warm quicker.
You may have timing issues or a worn injection pump. I just advanced my timing today and it made a bit of difference.
15mpg is normal for some of these trucks with differential gearing of 4.10 or 4.56. but it can also be low from bad inj pump, poor timing, bad injectorsetc...
I know some people say they can't climb hills but I've never experienced it. Some might say your truck is normal others that it's in need of work, alot depends on transmission and rear gearing.
The fuel filter (fire wall) is new. Previous owner said he wasn't sure if he sealed it right cause it kept losing it's prime? No clue if his is BS or what as I haven't had any fuel delivery issues for 3 weeks now.
your vibration issue could be from a few different things. can you cause the eng to vibrate at idle or only while driving? does it get worse the faster you go? If it is only when you are driving, check the U joints on your drive shaft. if the bearings start to go bad it can cause a really rough ride. all you need to do to check is remove the caps on the rear dif, slide the drive shaft up into the t-case, and spin the caps. if they just dried out you might be able to grease them up.
diaric: I was intending to invest in a compressor for the upcoming paint job, but this advice has accelerated that need. Thanks!
MrBanjo: vibration is only at measured speeds ( starts around 90 klics up through 115) with or without engine in gear so it's definitely a drive train issue. Pretty sure it's up front, but I've been wrong before. Is there a way to convict or clear the harmonic balancer?
short of pulling it, not that I know of. If it is the harmonic balancer you would have the vibration in or out of gear, not just while running down the road.
I'm down with the wheel balance issue. I have noticed when I get some slush/snow buildup inside my rims i will get some vibrating. a quick run through the car wash takes care of the problem.
I would rule out tire balance first. every vibration I've ever had has been solved by having the tires rebalanced. wear on tires is typically uneven, making it necessary to re balance. I usually have to have mine done about half way through the tread wear. I've never experienced an harmonic issue, but it seems that you would be able to make the truck vibrate while sitting still.
I have had U joint issues though, and yes they cause a heck of a vibration!
while the engine is running, open the t valve at the front of the engine, well find the hose that fuel is going to come running out of first and put that in a bottle. If the motor dies when you open the valve you have a bad lift pump ( i cant remember if 90 has electric or not)
You could try advancing the timing, but usually you will get good milage if the pump is retarded.
grab the outer part of the balancer and if it moves without the engine moving its bad. also you can look at the rubber from the back of it. if its all cracked and busted up its usually bad or on its way out.
I (ok "I" means my mechanic AND I) checked the u-joints and wheel bearings today. They all passed. He agrees it could be the tires. Time for a balance job!
oh lol. thats what i like about this forum. everyone jokes around and everyone has a good time and learns what they need to know.
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