E6 350 4v Short On Power, Worse Than Ever, Gutless!

[treemuncher]

I'm very glad to have found this website - THANK YOU, THANK YOU!!!

Patient: 1986 RW613 Superliner w/ Mack E6 350 4v motor, 13 spd eaton, 4:42 ratio, lacks power to get out of its own way

Symptoms: max about 950 degrees under load post turbo, max 22-25 psi turbo pressure depending on weather conditions, operates around 190 degrees on coolant temps, 30-65 psi oil pressure dependent on rpm's, air cleaner restriction less than 5 on the meter. Last pull home with 15k lbs on a 50 ton lowboy trailer - truck takes close to 1/2 mile to get to 55 mph on nearly flat ground. Some light smoke under load but not excessive. Truck is normally used to pull a 92k - 95k lb gross weight load.

Past history: Motor out of frame less than 10k miles ago, new rings & new bearings installed. Mack stamped .010 crank and all parts still showing hone marks & looking like new. Valve jobs done on both heads. Rebuilt injectors installed. Within last 5k miles installed a rebuilt fuel injection pump after old one siezed up. Mack set the fuel timing last year & dyno test showed 265 hp output. Repaired leaking intercooler last year. Puff limiter valve on front of AMBAC pump has never been connected or working to my knowledge.

The truck has always been slow but then again, it was always much faster than the old B61 I started with!

The truck sits sometimes for months at a time before it is used. My last check of the fuel flow looked good, the vent tube on the fuel tank is routinely checked as dirt dawbers have clogged that in the past causing problems. While the fuel filters have not been changed recently, they have not seen 3k miles yet. I do not believe that they are the problem.

I'm thinking that this puff limiter valve could be an issue although the injection shop made no mention of it when I got the rebuilt pump. I plan to go over the valve adjustment again while it is here at the shop. Last check of the turbo and the intake system looked good without any slop or serious leakage. The EGT seems low most of the time like there is very little fuel getting to the engine. Prior to Mack setting the fuel timing, I had timed it by ear and smoke and they said I was very close. It ran better the way I had it adjusted but it has always been slow on the pull. The dyno test proved my thoughts that this engine was putting out less than it should be.

Any suggestions to remedy this situation would be appreciated. I'm even considering turning up the pump if that will help. I've about had it with this old mutt and I'm thinking of looking for a replacement if I don't get it to behave!

[MACKS]

Sounds like it's not getting fuel, if the puff limiter is not hooked up it should be smoking like a freight train with thick black smoke.

[Maxville Truck]

Are you certain you have the ambac pump and not the robert bosch? If you have the bosch and the "puff limiter (Aneroid)" is not hooked up you will have a slugish low power feeling .... But as MACKS said

Sounds like it's not getting fuel, if the puff limiter is not hooked up it should be smoking like a freight train with thick black smoke.

You would have plenty of power. If you do indeed have the ambac and your puff limiter is hooked up your reverse relay valve could be faulty, someone correct me if Im wrong, Tha way the puff limiter works on the ambac, is compressed air goes through the reverse relay to the limiter cylinder on the pump under no boost conditions (idle), and as the engine builds boost it takes away pressure from the limiter cylinder and allows for more rack travel..

One thing I ran into with an 89 r model one time is one of the fuel lines had collapsed inside and restricted fuel flow bad enough to cut the power on the top end (4vh 350 ambac pump). We started replacing all the fuel lines around the filters and fuel pump of course it was the last one we changed that had the problem....

could be lift pump also good luck!!

[b61mack]

Are you certain you have the ambac pump and not the robert bosch? If you have the bosch and the "puff limiter (Aneroid)" is not hooked up you will have a slugish low power feeling .... But as MACKS said

You would have plenty of power. If you do indeed have the ambac and your puff limiter is hooked up your reverse relay valve could be faulty, someone correct me if Im wrong, Tha way the puff limiter works on the ambac, is compressed air goes through the reverse relay to the limiter cylinder on the pump under no boost conditions (idle), and as the engine builds boost it takes away pressure from the limiter cylinder and allows for more rack travel..

One thing I ran into with an 89 r model one time is one of the fuel lines had collapsed inside and restricted fuel flow bad enough to cut the power on the top end (4vh 350 ambac pump). We started replacing all the fuel lines around the filters and fuel pump of course it was the last one we changed that had the problem....

could be lift pump also good luck!!

I, like Maxville had the fuel lines collapsed on the inside , the long ones you might try blowing through, the short ones you could take off and look through them .

[Noid93]

A dyno test tests hp at the wheels, not at the motor, and i have been told that generaly you lose up to 10% of power per set of gears(i think thats a bit excessive) but by the time the tranny goes thru 2-3 sets of gears and then the rears(if you have mack rears also), you could be loosing 75 to 100 hp in no time. I dynoed a cornpicker with a dt533 motor(junk) that was recent remaned. So long story short, that pile should be 250 hp and was putting out 165 at the wheels in direct on the tranny. Im not real knowlegable on this but the math is close. Also, I feel the spec you should look at is torque. Hp(top end) maintains a working load, Torque(low end) gets you there (0 to 60). I have found torque to be a much easier sensation to feel on a truck. You cant have one without the other but torque seems to be the number that will fall off big if somethings not right.

Also, I drove the 89 R modle that MAXVILLE is talking about and for the E6 300 loaded to 90k with grain on, ONE MILE was not bad for 60 mph. One little secret of maxville and mine was putting the screws to it. We made a little smoke and watched the pyrometer and couldnt break 950 degrees. Im not asking you to settle for what you have, but as easy as some pumps are to turn up, the previous one could have been tweeked and after a reman process, they usually put them to factory.

Hope this helps

Noid93

Edited June 19, 2007 by Noid93

[Packer]

Noid93,

Back in the '60s and '70s, Consolidated Freightways ran two axle short COE.

These trucks ran a 6 speed only and were powered by both Cummins and Detroit engines.

They were used to pull doubles.

At the time, the thought was that every gear box cost 25 hp and by droping off one transmission and one drive axle, they 'picked up' 50 horses! There was also a fuel savings.

In real life, the Detroits were splitting in half, the Cummins pulled sleaves and fuel milage was the pits. (Maxidynes would have been the ticket)

I'm sure some pencil pusher came up with the idea, but I'm also sure that there is some truth about HP loss in gear cases.

Packer

[mudslut28]

Those e6 4v's were never noted for being big on power. They almost always need a shot of fuel if you want them to pull and for me they never even responded to that the way the 2v's did.. I had the e6 3004v and above 1600 power was non-existent. Torque seems to be their big thing. I'm betting yours is starving for fuel. I always turned mine up and watched the pyro to tell me when i got where I needed to be.

[GearheadGrrrl]

Even with a 350 horse motor, at US wide maximum weights (80,000 pounds) you've only got about 10 horses/metric ton. That will produce good performance for a truck, bit might still take 1/2 mile to reach 60 MPH. As for drivetrain losses, the standard figure I've read is about 2% for every gear reduction. That explains why many fleets use a direct drive transmission with single drive. BTW, while the double reduction Mack axles theoretically have more friction, in practice it works out about the same because their high input gives better driveline alignment and thus less friction in the U joints. As for direct drive, with engines putting our over 1500 lbs./ft. of torque the drivelines won't last, so overdrives have become a neccessity.

[treemuncher]

Thanks for all of your inputs. I ran the valve clearance again, checked and cleaned one injector (#6), turned up the fuel according to one of the posts I found on this site and checked for good flow out of the supply line. I would guess it pumped between 8-16 oz into the bucket within a 10 second cranking period. To me, that flow should seem sufficient. I would appreciate any comments on required flow rates and pressures that I should expect to the pump.

I took it out for a test drive with an empty trailer and it finally leaves a smoke trail like an old dog should. The pyro still only hit 950 pulling a long hill at 1200 rpms in top gear but the turbo was hitting 25+ psi on a summer day, which is better than ever. I won't know how much better it really is pulling until I move my trackhoe but it sure seems to be better than before. My lowboy has always been a tough pull compared to my old dump trailer, but the lowboy is what is used 95% of the time.

The only problem that I had turning up the fuel was that the adjustment screw was nearly at the end of its travel prior to my adjustments. Now it is at the end of its available travel. Does the little sloped ramp piece on the fuel stop adjust down? This would provide more travel if it did. I can see on there where the wear mark is from the previous adjustment and it looks like it used to run considerably more fuel than it currently does. This is a reman AMBAC pump that I got when my old one seized a few years back.

Anyone have any comments on an e9 500 hp mack v8? I had one dealer tell me they were junk. Others have told me they are real pulling monsters. I'm tired of dealing with this slow old dog of mine and I've been looking at CL's or CH's with 450+ hp, 18 spd and heavy axles. I want to move up to cruise control and a nicer ride for my longer trips. Got to live a little!

[Mack Doctor Jr.]

Sounds like its running better. Id still check the puff limiter most pump shops dont shim the correctly.(on the front of the injection pump) It usually causes low power on the low end. most of the time i just un hook it.

My 2 cents on the V8's is they arent junk.. Most of them had broken cranks cause noone would check the torque on the buttress screws. Other than that ive have not heard any bad things about em. If u ask me the horsepower is unbelievable it would be great for pulling a lowboy.

~Joe

[mudslut28]

LOL To drive an E9 is to love an E9!! Beware you will be smitten!!

[GearheadGrrrl]

My first experience with an E9 was when I made the mistake of getting into the Monfort (left) lane next to one stopped at a red light. The E9 was pulling a fully loaded flatbed, while my 6V92TT pulled but a light load of bread. I managed to stay with him for the first couple gears... Then he took off and I had to retreat in shame to the McLean's (right) lane.

[treemuncher]

UPDATE:

As of last week, I finally pulled my trackhoe home with the old dog. I usually gross about 92k - 95k lbs loaded.

Before following the posts on this site, every little hill knocked the tar out of my speed but now that the fuel has been increased to a more reasonable level, fewer shifts are required and you can finally feel the old dog pull. It is still a dog and slow to get to speed. I expect it always will be but at least, now it pulls with a firm grunt!

I think an adjustment of advancing the timing would probably help the horsepower but I doubt I will mess with it. I still don't get above 925-950 degrees on a long hill so I think that I can still increase the fuel rate IF I machine down the locking nuts within the fuel pump. These are currently maxed out but the old wear marks on the pump show that it used to deliver considerably more fuel than the current setting. I think the nuts were replaced during the rebuild and have a taller profile than the originals did.

Anyway, for a little increase in smoke, I've had a big increase in performance. Thank you to the members of this board who help others with your step by step instructions and all suggestions. I hope that I can share my expertise and help others in the future.

[dragonslayerpa1]

could someone please explane how to increase the fuel presure on my 350 mack i have a ambach pump i can only get about 850 on the pyro when pulling the mountians...very little black smoke and the no puffer valve the truck is very lazy.. been looking but cant find anywhere to help me out... thanks

dragonslayerpa1@yahoo.com

I'm very glad to have found this website - THANK YOU, THANK YOU!!!

Patient: 1986 RW613 Superliner w/ Mack E6 350 4v motor, 13 spd eaton, 4:42 ratio, lacks power to get out of its own way

Symptoms: max about 950 degrees under load post turbo, max 22-25 psi turbo pressure depending on weather conditions, operates around 190 degrees on coolant temps, 30-65 psi oil pressure dependent on rpm's, air cleaner restriction less than 5 on the meter. Last pull home with 15k lbs on a 50 ton lowboy trailer - truck takes close to 1/2 mile to get to 55 mph on nearly flat ground. Some light smoke under load but not excessive. Truck is normally used to pull a 92k - 95k lb gross weight load.

Past history: Motor out of frame less than 10k miles ago, new rings & new bearings installed. Mack stamped .010 crank and all parts still showing hone marks & looking like new. Valve jobs done on both heads. Rebuilt injectors installed. Within last 5k miles installed a rebuilt fuel injection pump after old one siezed up. Mack set the fuel timing last year & dyno test showed 265 hp output. Repaired leaking intercooler last year. Puff limiter valve on front of AMBAC pump has never been connected or working to my knowledge.

The truck has always been slow but then again, it was always much faster than the old B61 I started with!

The truck sits sometimes for months at a time before it is used. My last check of the fuel flow looked good, the vent tube on the fuel tank is routinely checked as dirt dawbers have clogged that in the past causing problems. While the fuel filters have not been changed recently, they have not seen 3k miles yet. I do not believe that they are the problem.

I'm thinking that this puff limiter valve could be an issue although the injection shop made no mention of it when I got the rebuilt pump. I plan to go over the valve adjustment again while it is here at the shop. Last check of the turbo and the intake system looked good without any slop or serious leakage. The EGT seems low most of the time like there is very little fuel getting to the engine. Prior to Mack setting the fuel timing, I had timed it by ear and smoke and they said I was very close. It ran better the way I had it adjusted but it has always been slow on the pull. The dyno test proved my thoughts that this engine was putting out less than it should be.

Any suggestions to remedy this situation would be appreciated. I'm even considering turning up the pump if that will help. I've about had it with this old mutt and I'm thinking of looking for a replacement if I don't get it to behave!

[Fastduramax]

OK Dragon Im prolly gonna get torched for this post but here is what I did.... My 88 E6 350 RD tri-axle went fom being the best running but most under powered 350 Ive ever owned or drivin to running like a scalded dog and still have the EGT's in check.... Pull the return line off your Ambac and then the brass fitting off the pump, there will be a small spring that sits in a small cup, find 3 small washers that will fit in that cup drop the spring back in and slam it back together.... My pressure went from 17lbs at idle to 28lbs.... I popped the top cover off my Ambac and slid the rack stop all the way forward, loosened the 3/16 screw on the ramp slot and slid the ramp all the way down to now get FULL rack travel.... Also changed the air cleaner in the process.... I went from a max of 16lbs boost to 24lbs and that is with some damaged fins in the compressor side od the turbo ! Yesterday I also adjusted the valves which were WAY out of spec and pressurized the system for boost leak test, hoping I gain even more as I have not driven it yet since yesterdays work.... Holy shit this truck came to life way more than I expected freakin actually fun to drive again !!!

[bullhusk]

Now on the back of the Ambac pump there is a plug, take that plug out,inside there's a long screw with an allen head turn that out 2an 1 half turns. Thats your GOV.ADJ.when the engine calls for power that rod moves foward to give the engine more fuel ERNIE PS KEEP YOUR EYE ON THE PYRO.

[Fastduramax]

Counter clockwise ?

[Fastduramax]

Any reason why 2 1/2 turns is the adjustment of choice ?

[bullhusk]

Yes, when you took the top off of the pump to turn your rack to full fuel,you could see the long screw about 2.5 inches long in the back of the fuel rack.When you start the engine, give it full throttle, you'll see that Gov. rod go foward an then slide back. Now, when you come to a hill or a hard pull, that Gov. will start moving foward giving more fuel to your engine giving you more torque or staying power,so, if you turn the screw counter clockwise the rod will go foward more.I don't advise this if you got a cowboy driving your truck though as you could blow it up! So watch your Pyro an down shift the trans. if the Pyro. starts to go where it shouldn't Ernie

[bullhusk]

2.5 turns won't get you in trouble, but i have a 1988 R model with a E6 350 thats turned out 5 full turns, but the truck isn't used much an when it is I drive it. A guy from Mack Truck Allentown PA. Came an turned our trucks back in 1987 when I bought 5 new Macks with EM6 300's 4V 6 Speeds. These trucks were so so bad I had no choice but to find a guy who (after hours) could help us out an boy when he did we were the cats meow on the jujtown. ERNIE.PS the Mack guy only turned our trucks 2.5 turns on the Gov. side that was because i had drivers on them

[Fastduramax]

Makes total sense Ernie thank you.... Opened my pump back up and made the 2 1/2 turn adjustment, Ill report tomorrow night on any improvement I may see.... My ass is the only one in the seat of my truck ever and is fully equiped with autometer digital gauges so I dont mind playing around with power settings....

[Fastduramax]

Ernie What are you seeing for no load full throttle RPM ? Im currently seeing 2200, a Mack mechanic told me years ago he likes to see 2300 ??

[bullhusk]

Mine tach's out @ 2300 but if it's a mech. tech it could be off a little, an remember those 1800 rpm motors are only about 2000 to 2100 no load an some of those pull ok ERNIE

[Warpman89]

OK Dragon Im prolly gonna get torched for this post but here is what I did.... My 88 E6 350 RD tri-axle went fom being the best running but most under powered 350 Ive ever owned or drivin to running like a scalded dog and still have the EGT's in check.... Pull the return line off your Ambac and then the brass fitting off the pump, there will be a small spring that sits in a small cup, find 3 small washers that will fit in that cup drop the spring back in and slam it back together.... My pressure went from 17lbs at idle to 28lbs.... I popped the top cover off my Ambac and slid the rack stop all the way forward, loosened the 3/16 screw on the ramp slot and slid the ramp all the way down to now get FULL rack travel.... Also changed the air cleaner in the process.... I went from a max of 16lbs boost to 24lbs and that is with some damaged fins in the compressor side od the turbo ! Yesterday I also adjusted the valves which were WAY out of spec and pressurized the system for boost leak test, hoping I gain even more as I have not driven it yet since yesterdays work.... Holy shit this truck came to life way more than I expected freakin actually fun to drive again !!!

Hey man i have an 88 also with the same engine and pump combo, so you caught my interest when you said your boost went from 16 to 24

if you have some pictures of this modification so i can better understand the procedure, i would greatly appreciate it

keep on truckin!

[bullhusk]

Well Fastduramax,

Tell us all how the truck is running !!!

BULLHUSK