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motts

help to diagnose a sick r model

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Hi, ya'll i have a 1987 rss 688lst with a E6 4 valve well it starts and runs it just don't seem to make any power no black smoke slow to rev and build boost it has new fuel filters and a lift pump where do ya'll suggest i should start troubleshootin this thing i don't much know how on these here things any help would be greatly apprieciated

Thank you

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Not sure but years ago in a company truck I had similar problem. I think it was governor in pump that failed. I know we ended up changing pump. Hopefully someone on here can elaborate.

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My '90 RD had a bad diaphram in the aneroid valve,that wouldn't let the rack open all the way. No smoke,little power. Not saying thats your problem,but something to check anyway.  Al

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Put a T fitting and gauge after the transfer pump to verify fuel pres. It should be between 17-31 PSI under load.  Going to be hard because you can't get RPM out of it but you may have a clogged or collapsed fuel line between the tank and transfer pump.

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17 hours ago, 57 bcr said:

My '90 RD had a bad diaphram in the aneroid valve,that wouldn't let the rack open all the way. No smoke,little power. Not saying thats your problem,but something to check anyway.  Al

yes i found that was bad and i replaced it and that did not solve the problem which is why i ended up here you guys are awesome thank you 

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15 hours ago, j hancock said:

Put a T fitting and gauge after the transfer pump to verify fuel pres. It should be between 17-31 PSI under load.  Going to be hard because you can't get RPM out of it but you may have a clogged or collapsed fuel line between the tank and transfer pump.

i will give this a try i blew thru the lines when i replaced the lift pump and they seemed fine but as the wife says blowing and sucking ain't the same thing  

and a little update as i been poking around at it i rigged up some caps and did a leak test on the air charge cooler and it held 30 psi with no leaks 

this old dog has 670000 on the ticker i don';t know if the engine has ever had any werk performed on it or not but it does look like someone has been messin with the governor on the pump as all the wire dohickeys that hold the adj screws are missin. 

i went and yanked out the fuel injectors gonna send them out for testing i was gonna pick up one of them diesel compression test kits from the harbour co. and see what the compression is on it do you know what kind of numbers is should be seeing on it

Thank you

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About 450-460 PSI new.  After half a million miles will be less.  Consistent PSI range from front to back hopefully.

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ok i so i picked up the the tools a did a compression test and good thing all cylinders were equal with that being said 400 psi is what i seen but i ask ? should this be seen on the 1st compression stroke as this took 3 bumps on the gauge to hit the 400 mark 1st hit on most  cylinders was around 250 and also the injector shop said that 5 of the 6 injectors were leaking and had bad spray patterns still waiting to get the rebuilts back. 

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Sounds about right on the compression test.  Usually takes 4 or 5 hits for the PSI reading.

Would be nice if it was a little higher a number.

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the no smoke issue on a e-6 sounds like a fuel issue for sure, or perhaps the air cleaner in upside down, but I would think you would still have smoke, but it would make for a lazy engine response.   

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if you dont have no smoke you arent getting enough fuel to leave smoke 

This could be a range of issues if the fuel rack isnt moving all the way because the governor isnt working right this could be the problem

Or maybe a lack of fuel from the tank 

If it was a lack of air it would be making heaps of black smoke as the fuel wouldnt be getting burnt because of a lack of air 

Or at least this is what my brain tells me 

 

 

Paul

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Thank you for the replies after i get the rebuilt injectors back in it i will test the pressure after the lift pump and let you what that is.

Thanks again

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so i picked up the injectors and the new o ring kit has only 2 orings and 1 sealing washer and the manual and my memory tells me that there are 3 orings and 1 sealing washer and both the stealership and the injector shop are telling me i only need 2 but i am getting conflicting information as to which groove the little o ring goes into stealership says use the bottom slot and the injector shop says use  the top slot and leave the small weep hole exposed to cool the cylinder.

so can anyone  tell me which is right 

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Double checked a 1984 Mack manual and it shows a top O ring seal.  Then 2 O rings about 1/3 of the way down either side of the weep hole.  The bottom has gasket at the injector nozzle.

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yes mine too so that is what i went with if you have to do these orings the kits from the dealer will only supply you with one of the smaller ones which is what brought about this dielemma any way back to the patient injectors are back in and fired it up 20 psi on the lift pump at idle it didnt seem to change any when revved up. still only seeing 2 psi on the boost gauge and engine is slow to rev and exhaust color is mostly a blue color no black what so ever     so i take it that it is most likely a gov/inj pump issue       what do you suggest i should do from here?

Thank you

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Seems like a party with partying down the governor is coming.

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Pressure test the aftercooler for leaks.

 

FW

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10 hours ago, motts said:

yes mine too so that is what i went with if you have to do these orings the kits from the dealer will only supply you with one of the smaller ones which is what brought about this dielemma any way back to the patient injectors are back in and fired it up 20 psi on the lift pump at idle it didnt seem to change any when revved up. still only seeing 2 psi on the boost gauge and engine is slow to rev and exhaust color is mostly a blue color no black what so ever     so i take it that it is most likely a gov/inj pump issue       what do you suggest i should do from here?

Thank you

My RW had a similar issue. The injector pump has a splined shaft that the throttle linkage connects to. The splines are worn off, and the throttle linkage would work as it should, but it would just spin on the the shaft coming out of the injector pump. Truck would rev up all the way with no load, but was a complete dog under load. 

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Sounds to me like the puff limiter is stuck out on the injector pump. 

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only 2 psi of boost tells me no fuel. I had a bad turbo once and it still made 14psi of boost under load. if its not the injection pump it could also be a restriction in the fuel hose or in the bottom of the fuel tank. try running it out of a 5 gallon jug and see if it runs better. if it does you have a clogged fuel line. if no change start looking at the injection pump. the E6 should make about 25psi of boost under load.

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Unscrew the puff limiter out of the injection pump and run it. 

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i don't  have any info on the gov/inj pump is there anything i could do to check the gov for proper operation or how do you tell if the rack is getting full travel?

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On 2/10/2017 at 8:24 PM, RSD501 said:

My RW had a similar issue. The injector pump has a splined shaft that the throttle linkage connects to. The splines are worn off, and the throttle linkage would work as it should, but it would just spin on the the shaft coming out of the injector pump. Truck would rev up all the way with no load, but was a complete dog under load. 

i will look into this

Thank you

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the shaft and spline connection seems fine everything is rotating in sync 

shure seems to be gov/ pump related  is there anything else i can do or check out or is it best now to take it in and let pump  shop pull the pump and do the reinstall as i dont have the timing light tool to reset the pump engine timing 

one last thing i am going to check into is the manual talks about a fuel overflow valve on the pump may be faulty is there anyway that this can be checked out or just replace it?

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here is the latest info i can provide i took for a run with a boost gauge finally in the cab and what i am seeing is it will only get about to 5psi boost in low range before it revs out and in top gear i seen 18 psi once mostly it was around 16 psi so am i still chasing a fuel issue? 

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I think before i started taking the pump off I would try what Dirtymilkman suggested.  Check the puff limiter rack limiting cylinder on the front of the pump.  

Before you do this …. If you mash the throttle with the brakes on , does it blow black smoke ?  From what you said it won't , I just wanted to make sure you did this simple test

to see if it is pump related or puff limiter related.  

My 350 4V seemed lazy . It would only get boost around 1600 - 1700 rpm . It turned out to be the puff limiter relay valve  on the manifold. 

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