odiie

Name: Mack R688ST (1986)

Date Added: 06 September 2009 - 03:18 PM

Owner: odiie

Short Description: None Provided

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Thanks Rob, yes it does run fine once started. I'll try the temp line.

First thing I would do is remove the fuel line that is from the tank to the inlet of the filter housing. Replace this with a temporary line into a supply of diesel fuel from a can on the floor. Get the engine started and running smooth, then shut it off. Let it set the amount of time that you had trouble with prime loss and see if your temp line solves the problem. If it does, replace your suction line. If it does not and you have an inline check valve, ensure it is good, or replace it for good measure.

If it is losing prime, it is most likely due to air getting into the system from a pinhole in a line, or a drainback from some type of check whether it be a valve, the transfer pump valves, or whatever else is in the low pressure side of the system. Chances are with the engine starting right off, running a short while then dying out, it is starting on the fuel gallery storage within the pump. It runs until this supply is exhausted. The transfer pump overpowers the drainback leakage to the line and eventually refills the pump gallery and the engine restarts as you grind on the starter. This assumption is that your primary, and secondary fuel filters are physically mounted lower than the injection pump, otherwise you would drain your filters down and need to refill them to restart the engine.

I have also seen plunger barrels so worn out the truck would be difficult to start, idle fine, but have limited power when asked to deliver fuel.

I'm assuming your truck runs well once started.

Rob

My new pride and joy starts right away but only fires a few times then it cranks for quite a while. Where is the most likely place that I'm losing my prime. I assume thats what is happening. No obvious outside leaks. How do I diagnose this? Any help appreciated.

Thanks for the information fellas.

That "Dynamat" is some good stuff I'll tell you. For dinner(s) last week I had baked beans, jalapeño laced taco sauce for my burritos, a whole head of cabbage with my corned beef, plus drank nearly a gallon of spiced tomato juice from some of Other Dog's garden tomatos. On top of that I finished off a large bowl of mustard potato salad and 1/2 dozen of deviled eggs. Momma cooked me up a few hard boiled eggs too but I was too full to finish em.

When my bowels started to get a little "queezy", I fashioned a diaper from a 3 foot square section of "Dynamat" and headed to the public library downtown; (still haven't fixed the floor under the toilet at home). Upon backing up to the HVAC inlet I was able to practice flatulence in E minor, and C sharp, with nobody hearing nothing! That stuff sure does mufflle sound!! With the exception of a filtered air silent tornado, all was unoticed. I had to grab my cheeks to cease the flap, and depart quickly as a "Funk" filled the building. I surely didn't want to get blamed for something I didn't do.

That "Dynamat" stuff is pretty good. I think I'll use it in my truck. Best of all, it is not an irritant and is hypo-allergenic.

Actually, I've used several variants of "Dynamat" and there are many product just as good in quality that are less expensive to purchase. The more dense the media whether it be fiberglass, closed cell foam, or any of the like sound attenuation and difusion media all work well. If you go this type of route be sure to get the Mylar faced material which will serve to reflect the radiant heat that comes through the firewall from the engine. Use a heat resistant adhesive to adhere the material to a cleaned substrate . You will also need to cover the insulation blanket with some type of cap. I would get a sheet of black vinyl material and glue this to the mylar face of the blanket. Vinyl sheeting is readily available from most upholstery shops. One other thing; Ask if the vinyl is UV stabilized so it will not fade with sunlight.

Rob

I'm trying to find a new firewall insulator for my 86 R688. Mack says it is not available. Where can I get it or what can I use as an alternative?

idle stop yes. you were told it had a miss? Do you hear a miss?

I can't hear a miss it just sounded strange because of the high idle I think. Just makes me wonder if I'm missing something ya know?

Couple of questions, I just bought an 86 R model with a 350 6 cylinder in it. I was told it had a miss in it but it drops rpm on all cylinders if you crack injection lines. Any other way to find a miss? It was idling at around 800 rpm because of a jake switch interfeering with the throttle rod. Could it have sounded like it was missing because of the fast idle? Also on the injection pump right above the throttle shaft is a screw in a long locknut(the nut is about half inch high) what is it for? Idle stop? Thanks for your help.