macksmoke Posted November 3, 2014 Share Posted November 3, 2014 Hi guys. I work for a small town and been here about a year. The truck I'm plowing with this year is a 1990 RD688SX. From what I hear is that there is only 8 of these made, its a old NYC fire truck. Now it has a 10 yard sander in the dump body with a 10 ft. plow on the front and a 10 ft. wing plow. The problem is that it has no power, from a stop up hill I wait about 20 seconds for the boost to build enough to move and sometimes thats not enough. I just did a valve adjustment and all filters are changed. I would like to turn this up but the place I was going to bring the pump to wants $1600-$1800 and I don't have much money to spend. Also I'm worried about the automatic Allison thats in it. Is there something that I'm missing? Or is this just a 270HP engine? Thanks for any feedback!!1990 RD688SXEngine:E6-270Serial# 0B095411GBA75936Inj. pump:Bosch#95110112Trans:Allison model#HT750-DR Thanks, Steve. Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/ Share on other sites More sharing options...
j hancock Posted November 3, 2014 Share Posted November 3, 2014 Are you loosing boost through a faulty air to air exchange, bad hose connection or bad hose? Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265482 Share on other sites More sharing options...
General Ike Posted November 3, 2014 Share Posted November 3, 2014 I'm nearly positive that there were no FDNY rigs that ever ran the RD model as a piece of front line apparatus. In 1969-1970 a handful of R model crew cab pumpers were delivered.... Mack did run a handful of RD's in support roles as wreckers and carrying roll-offs and maybe even as fuel rigs. But they never ran an RD as a "fire truck" Quote Ed Smith1957 B85F 1242 "The General Ike" Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265505 Share on other sites More sharing options...
macksmoke Posted November 4, 2014 Author Share Posted November 4, 2014 Sorry guys, its a old NYC truck. I'm not sure if its highway or sanitation or PW. It was a bright lime green when we got it and it had a plow on it. Anyways I dont see any turbo leaks and the turbine seems good. I don't seem to have any fuel restrictions, (return or feed). All cylinders are running about the same temperature. What I don't understand is why it takes so long for the boost to build, (15-30 seconds)? It's so bad that if I was loaded and came to a stop uphill, I may not be able to pull away! Sometimes I have to back up and get a running start. Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265574 Share on other sites More sharing options...
macksmoke Posted November 4, 2014 Author Share Posted November 4, 2014 Are you loosing boost through a faulty air to air exchange, bad hose connection or bad hose?I don't seem to have any air leaks, just low HP I think. Where in N.H. are you from? I'm in Wilton. Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265578 Share on other sites More sharing options...
Dirtymilkman Posted November 4, 2014 Share Posted November 4, 2014 Sounds like the reversing relay on the intake or the puff limiter is bad. Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265590 Share on other sites More sharing options...
gearhead204 Posted November 4, 2014 Share Posted November 4, 2014 are you getting FULL throttle at the pump? the lever on the side of the pump that the throttle pedal linkage hooks to should hit the internal pump stop , and then OVER TRAVEL a little as the throttle pedal hits the floor/stop. Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265623 Share on other sites More sharing options...
Popular Post MACKS Posted November 5, 2014 Popular Post Share Posted November 5, 2014 I have the same plow truck from nyc same year same engine same tranny,I could pull a house down with this truck it has amazing power for a 270 hp,pulls the same empty or loaded it just goes and its not turned up at all as far as i know.. 3 Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265668 Share on other sites More sharing options...
macksmoke Posted November 5, 2014 Author Share Posted November 5, 2014 Hey Macks, thats the same truck! I guess NYFD ordered 6 of theses as tankers, the at some point the put dumps on them to haul aspalt. I'll send some photos wen I get home today. How can I go about testing the puff limiter and relay? Thanks, Steve. Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265717 Share on other sites More sharing options...
Dirtymilkman Posted November 5, 2014 Share Posted November 5, 2014 The puff limiter is located on the injection pump. It's about 3 inches long, cylindrical shaped with a air line screwed on the end of it. The puffer is screwed into the injection pump horizontally at the end of the injector rack. If you unscrew the air line and cap it off and then unscrew the puffer out of the injection pump. This will allow the injector rack open all the way when you drive without having to wait for boost to build. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265723 Share on other sites More sharing options...
macksmoke Posted November 5, 2014 Author Share Posted November 5, 2014 Is the puffer screw at the front or the back of the pump? Does it come out and do I have to plug the hole after? Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265727 Share on other sites More sharing options...
Dirtymilkman Posted November 5, 2014 Share Posted November 5, 2014 Its on the back of the injector pump. U should cover the hole. When you release your brakes air is sent to the puffer and it pushes out a little pecker that keeps the rack from opening. As boost pressure builds in your intake that builds pressure in the reversing relay which then allows the puffer to back off more and more. I always just took the puffer off, applied shop air to it and cut off the pecker on it. Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265744 Share on other sites More sharing options...
mrsmackpaul Posted November 6, 2014 Share Posted November 6, 2014 Its on the back of the injector pump. U should cover the hole. When you release your brakes air is sent to the puffer and it pushes out a little pecker that keeps the rack from opening. As boost pressure builds in your intake that builds pressure in the reversing relay which then allows the puffer to back off more and more. I always just took the puffer off, applied shop air to it and cut off the pecker on it.you might wanna bung some photos up to explaine what your talking about you no the old saying about a picture been worth a thousand wordsPaul Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265747 Share on other sites More sharing options...
farmer52 Posted November 6, 2014 Share Posted November 6, 2014 Its on the back of the injector pump. U should cover the hole. When you release your brakes air is sent to the puffer and it pushes out a little pecker that keeps the rack from opening. As boost pressure builds in your intake that builds pressure in the reversing relay which then allows the puffer to back off more and more. I always just took the puffer off, applied shop air to it and cut off the pecker on it.Is that a new technical term? 1 Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265748 Share on other sites More sharing options...
Dirtymilkman Posted November 6, 2014 Share Posted November 6, 2014 Those are the scientific terms. 2 Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265749 Share on other sites More sharing options...
Dirtymilkman Posted November 6, 2014 Share Posted November 6, 2014 I'm horrible at explaining and my old ch is on the road. Everything else I have is newer. Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265750 Share on other sites More sharing options...
macksmoke Posted November 6, 2014 Author Share Posted November 6, 2014 Sorry guys! My pictures aren't showing up. The puff limiter on this is on the back about the throttle or govenor. I really cant find a small pecker anywhere! (I'm French!) I can't even find a relay valve on the intake. The air line to the puff limiter comes from the intake manifold direct. It seems like the vaceum from the manifold controls the puff limiter. Thanks again for all your help! Steve. Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265766 Share on other sites More sharing options...
theakerstwo Posted November 6, 2014 Share Posted November 6, 2014 Yes and a lot of bad info on here. Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265768 Share on other sites More sharing options...
Dirtymilkman Posted November 6, 2014 Share Posted November 6, 2014 If that air line is coming direct the puffer will be doing opposite of what it should. Also the only way I can post pics on here is to use the desktop site. Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265775 Share on other sites More sharing options...
MACKS Posted November 6, 2014 Share Posted November 6, 2014 Try this test and see what happens,warm up the engine and with the maxi brakes applied snap the throttle to full open,you should see a nice puff of black smoke come out the stack,then with the brakes released do it again,now there should be little to no black smoke.If you dont get that black smoke with the brakes applied I would look for a fuel restriction or maybe a pin hole leak in one of your fuel lines.I will take a look at mine and see how its hooked up,will check in here later. Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265802 Share on other sites More sharing options...
macksmoke Posted November 6, 2014 Author Share Posted November 6, 2014 I get some smoke with the brakes applied also when I'm trying to go from a stop. It takes about 15 seconds for the boost to build enough to climb out of a hole. The air line that feeds the puff limiter comes from the intake manifold with nothing in between. There is also a fitting on the side at the front of the pump with a air line on one side and a fuel line on the other. I think it's the return line? I'm going to keep trying to get a picture on here! Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265803 Share on other sites More sharing options...
MACKS Posted November 6, 2014 Share Posted November 6, 2014 The puffer on these engines are very different from what these guys are talking about,im not sure how to dissable it and to be honest i dont think thats your problem,does your truck have and air throttle like mine if make sure its working right,have some one watch the the lever on the pump when you apple the throttle from inside the cab. Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265805 Share on other sites More sharing options...
macksmoke Posted November 6, 2014 Author Share Posted November 6, 2014 I thought the puffer was different! Yes it has a air throttle and it is going wide open. This thing is bad we had a load of sand in it when we first got it and we back in some soft sand, we had to pull it out with the loader because it didn't have the power to climb out. When loaded it will not climb a hill out of 1st gear! Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265808 Share on other sites More sharing options...
macksmoke Posted November 6, 2014 Author Share Posted November 6, 2014 Yesterday I disconnected the air from the puffer and plugged it, took it down the street and it was far worse the before! Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265809 Share on other sites More sharing options...
MACKS Posted November 6, 2014 Share Posted November 6, 2014 Yesterday I disconnected the air from the puffer and plugged it, took it down the street and it was far worse the before!That line comes from the manafold right,when the air pressure builds in the manafold it goes through that line to the puffer and alowing the rack in the pump to open,that means the puffer is working assuming your getting enough air to it for it to open fully,if your turbo is working ok and air filter is not plugged and that air line is clear then i just think you have a severe fuel restriction problem,hope you figure it out,youll be amazed how that truck pulls a load down the road. Quote Link to comment https://www.bigmacktrucks.com/topic/37599-my-truck-needs-more-power/#findComment-265812 Share on other sites More sharing options...
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