ENDT864 Twin Turbo V8 engine Power

[Phil Bennett]

Hello,

Wonder if anyone out there can offer any views / comments on my 'problem' ?

I have a 1970 R719 with the ENDT864 twin turbo V8 fitted, all pretty original.

Understand that engine should deliver around 300hp, but was not Macks finest and had 'issues'...

My Problem: Thought not used for everyday haulage (just shows), if I pull a ballasted 20' container (32 tons), I struggle to get much 'get up and go' over 35mph.

As if the 300 hp is just not there.

On a slight downhill road, it can (and will) do 50 mph.  But a slight incline, not really.

Compression fine.  Injectors fine (clean exhaust), fresh diesel, filters and replaced fuel lines.  Fuel pump pressure as per Mack manual.

Checking the Turbo boost pressures (no gauges fitted, but have added aftermarket to be able to check) only give (under load pulling 32 ton)

 

Mack Max RPM = 2300

 

1600rpm – 1800rpm = 2 to 4 psi.

 

Best PSI reading is just about 5psi when accelerating up to 2000rpm.

Am I expecting too much in the way of 'performance' from a truck of this age / era / horsepower ?

Thanks

Phil

 

 

 

 

[j hancock]

Not enough boost!  Time to check the turbochargers.  Also check for leaks on the compressed side.

[JoeH]

+1 on boost. Every Mack I have puts out around 25psi boost, and yours isn't much older.

1979 r686st,

1980 dm686sx,

1995 rd688s

Disconnect puff limiter, see if you get a cloud of black smoke when you gun it. If you don't then you could have fuel issues.

[AZB755V8]

8 hours ago, JoeH said:

+1 on boost. Every Mack I have puts out around 25psi boost, and yours isn't much older.

1979 r686st,

1980 dm686sx,

1995 rd688s

Disconnect puff limiter, see if you get a cloud of black smoke when you gun it. If you don't then you could have fuel issues.

No can do on this engine, no puff limiter and boost is less than 12 psi max on the twin turbo set-up. 

Clear no smoke exhaust, Pump needs turned up plus turbo boost is low. Injectors may be fine but that old spider pump need to put out more fuel. Then worry about turbos and boost psi. For hobby I would not worry about low power unless you plan on pulling 32 tons to a show.

Check pump timing as it can be off wit not enough advance.

[Rob]

10 - 11psi is what you would normally see on those engines when they were running well under a good load. Used to work for a place and swapped one for a six cylinder as couldn't keep it reliably running and it was in that range of boost pressure. The other R model with that engine was too far gone, (rust) to work with although it too was problematic to keep operational. The same party purchased both the truck, and then spare engine in some kind of deal.

As mentioned look at the fuel pump as it sounds as if you are just not getting enough fuel as the root cause. That engine should smoke pretty fair under a pull just off of low idle speed before the turbochargers have time to spool up. Both I was around did when they were running well.

[Freightrain]

Is the throttle linkage working?  Getting WOT?

I know the arm on my 237 pump come loose and it would drop boost/power randomly(as it slid on the shaft).  After addressing the clamp it holds fine.  You could drive it, but under a load it would not pull(due to lack of fuel and boost).

[Phil Bennett]

Hello Larry,

Thanks for comment.

In answer to your suggestion, "No", I do believe the linkage is working just fine.  But I will double check tomorrow.  Ironically I did have an issue with the linkage in that it was 'catching' on one of the exhaust clamps, but that was easily solved by loosening clamp and swivelling round.  I am aware that the external  'arm linkage' (which is connected to the throttle rods) on the side of the pump is kinda 'spring loaded' (looks by design) to avoid overstraining said arm when throttle at full stretch.

General consensus seems to be that the engine is running too lean (and that the turbos may be a little 'tired', though the lean fuels seems to be the first place to start.

Understand I need to slightly adjust the stud (slacken lock nut first) by winding 'in' 1/4 of a turn...  See image enclosed.

Thanks

Phil

 

[Freightrain]

Have you checked fuel pressure?   That was the second stage of my lack of power issue I had the second year I had the 237 in my truck.  First the bushing on the throttle arm.  Once I fixed that it started loosing power on hills, randomly.  I finally put a fuel pressure gauge on the pump and hung it on the air filter so I could watch it running down the road.  I had very low pressure, like 5 lbs at idle and it would drop off under load.  I replaced the lift pump and suddenly I had 20 psi at idle and about 10 under load.  Truck runs fine.

 

Oops, just reread your post.  Says pressure was fine.  But is that under load?

Edited May 29, 2019 by Freightrain