Throttle pedal response question

[HeadWizard]

I just got done driving both my '66 M35A2 and Shorty the Bobbed Deuce (1970 M35a2) and I noticed a very different response from the throttle pedal between the two of them. Just to make this clear, I'm talking about throttle response when running and in neutral - no load. Shorty obviously doesn't accelerate that great with the 16.00-20 XL's.

The '66 has a very crisp and quick increase in rpm's with a blip of the throttle pedal. It's very easy to rev it to 2500 rpm. Shorty on the other hand is much more sluggish, definitely taking more time to rev up. Both Trucks have LDT465-1C's in them and they both have Whistler turbos.

Shorty also exhibits another odd symptom. While it starts almost immediately when the start button is pushed, the rpm's remain very low (400-500) until you blip the throttle pedal (or use the hand throttle). It then levels out nicely around 800 or so rpm.

I know this is more of a perceived issue, but there is definitely a BIG difference in the way the two trucks react to throttle input. Could some of you experts please ponder up some potential causes and fixes for this problem?

 

[Jones]

If you've got good power throughout the RPM range I might look at the injection pump; either timing or sticky governor components. If it's sluggish or falls off towards the higher engine speeds then maybe it's a fuel problem like filters partially clogged or weak in-tank pump.

 

[Westech]

it also depends on how much the fuel is turned up. mine is like a race car motor and will bounce off 2900 rpm right NOW! you can just put a flat or two in the adjuster and that may help.. also check fuel filters. that could cause sluggish a response

 

[dirtyfingernails]

Headwizard,
My duece was acting the same at startup. If you didn't goose the throttle it would rough rough at 400 rpm. I bled my fuel system and the problem went away. However, I started it this evening with the same problem again. I think I may have leakdown. Air is getting in somewhere. Tomorrow I'm going to try to let the in tank pump run a minute before I try turning it over. If you find something different, please let me know so I can look into it also. Thanks.
Steve

 

[rmgill]

PM the ENTIRE fuel system first. Filters, check for lines that are crimped, clogged pickups and trash in the tank. Drain the sump on the tank and look for water. I had a 5 ton that would run fine, then get down the road and the rpms would float and not drop back down BUT power would be off, I'd sort of languish a bit in 4th, usually on a hill, then when it was finally time to downshift to 3rd and I had a line of cars the power would come back on. I chased that around by checking the filter a bunch and it turned out it was a combination of sludge/water in the fuel tank AND a bit of plastic wrapper from a soda can in the fuel pickup blocking fuel flow. I pulled all that out and it ran like a champ.

 

[HeadWizard]

Thanks for the info so far.

The filters were just changed and the fuel is fresh diesel. It appears to have consistent power through the rpm range, though not what the other truck has. Doesn't really blow any smoke whatsoever. The low idle at start up is troublesome and certainly could be leakdown somewhere, but seems strange that it will idle that low for an extended period until the pedal is blipped. There are no fuel leaks.

I'm going to check further on sludge, crud and whatever in the tank. If there were clogs, etc wouldn't there be a real problem at WOT? Maybe I do need to try turning up the fuel a flat or two?

Thanks again for the suggestions - keep them coming.

 

[Westech]

mine smokes like a fright train! Turn that fuel up a tad!!

 

[Jones]

A clog may be intermittant if whatever is the problem is loose in the tank or system. When it floats over to an orifice and gets in the way then your problem shows itself. I've seen leaves, bits of plastic wrapper, bits of duct tape, water at just the right level, a 'personal hygenic protective device'-- in fuel tanks. Sometimes the inner layers of rubber-lined fuel lines delaminate and act as dams; ballooning and blocking the passage or deflating back to normal. It's often what you dismiss as 'couldn't possibly be it', so a full shakedown of the fuel system may be in order. Might be time to run a few cans of fuel injector/fuel system cleaner through to get the gunk moving so that the filters can trap it. A tip: You said your filters are fresh but I've seen people driven to distraction with the runs-great-at-low-speed-but-like-hen poop-at higher-RPMs syndrome; turned out to be a paper element filter with the paper saturated with water which closes the pores and keeps fuel from flowing through.
Hitting the throttle and having things settle down keeps making me think of sticky governor weights; which a dose of fuel system cleaner will also help.
Could be something as strange as a bad electrical connection which sometimes interferes with the in-tank pump being able to fully do it's job. You just never know.

 

[jeli]

I've got the exact same thing. Hit the start button and it pops right off. I always work the pedal until it gets going above 500 rpm. My 1C is idling at 900 to 950. I haven't had time to turn it down a tad nor do any PM on it since buying it.

 

[m-35tom]

very poor responce at low rpm is possible if the droop adj is off or the ip head is worn. check for 5 psi at 1500 rpm at intake manifold. (this is at WOT)

 

[HeadWizard]

very poor response at low rpm is possible if the droop adj is off or the ip head is worn. check for 5 psi at 1500 rpm at intake manifold. (this is at WOT)

sorry to be ignorant but what is �droop adj�? Also, 5 psi of what at the manifold? Manifold pressure, fuel pressure?

Thanks for the help. Also glad to see I'm not the only one with the �won't idle at first� issue.

 

[m-35tom]

see the ip manual for adj, it is through a plug in the rear of the govenor housing. 5 psi at the manifold is boost pressure, if you do not have a turbo you won't be able to do it this way. i have found several trucks that fall on there face when you want to start out at low rpm and always backing the droop out a little fixes it

 

[acetomatoco]

Oh no... the dreaded manuals... see what I mean!! Read em in bed and then buy the truck...

 

[cranetruck]

Don't believe that's covered in the TMs (what Tom is talking about...).
IMHO getting info from a person/teacher is more fun and fullfilling than reading the textbooks alone.

 

[m-35tom]

ace, you're not keeping up... i used 'there' incorrectly and you didn't catch it. well it is in some manual, 'cause i used to have several pages of it but can't find it now. details on how to check and adjust fuel rate in the field so to speak. head, how does that truck perform with those big tires? about like my .71 od project in respect to final gearing.

 

[DDoyle]

I'm with check the simple stuff first - it needs to be done anyhow. Also verify that the intank fuel pump operation is consistent. Turn pump on a bang-on, try to shift, the tank. I too have the publication concerning droop screw settings - don't remember if it is in the IP manual, or if it is in an engine manual, or even in one of the LDS-427 related pubs (I think the later) - and since I am in Dayton, can't look!

Best wishes,
David

 

[cranetruck]

Since you are on line David, do you know of an official procedure for bypassing the FDC and the necessary re-adjustment of the fuel delivery?
According to the TMs, few if any of the IP adjustments are to be done "in the field", so why would the droop screw be suspect?

 

[dirtyfingernails]

Headwizard,
Keep us informed. My did it again tonight. I had to goose the throttle twice and it ran perfect after that. All fuel filters are new, tank was drained completely and replaced with fresh diesel. No smoke whatsoever unless you hit the accelerator, then it's only a brief puff of grey. I let the pump run for 1 minute before starting, but that didn't help. Fires right up everytime though!
Steve

 

[HeadWizard]

Thanks for all the info. If anyone can find/provide procedures/pics of the droop adjustment that would be great. Fuel system is supposed to be PM'd tomorrow to make sure all is good. Will also check fuel pressure at tank and after filters. Plan to add a good dose of BG 44K for diesels to get everything else cleaned internally.

Someone talked about governor weights possibly being a problem? What TM?

Also going to make sure all linkages and cables are lubed properly and work freely. Tighten up all connections to make sure no bleed down of air infiltration.

As to how it performs... if I use only high range, it's about how you'd expect, like a dog. When I use the modified shift pattern starting out in 2nd low thru 5th low then 4th and 5th high it works pretty good. Haven't spent the time to do the math of effective gear ratio with the larger tires (51� high measured). Speedo is way off - wish I could fix that, but it will run 70mph on the highway with not much problem. Amazingly stable on the interstate but wanders pretty bad on the back road. I'm planning to get a leaf or two added to each spring to firm it up and source corresponding shocks to match.

This is not a serious off road truck, but rather a part time fun driver. You wouldn't believe how many times I've heard - What the heck is that?

Thanks-
Don

 

[m-35tom]

with that size tire 2500 rpm = 71.4 mph the gears i am having made will give 65 mph at 2500 rpm with 14.5R20 or 11:00-20 tires so wanted a comparison, thanks