7780z stumble under load. 5k rpm 1st gear,4k in 2nd,3k 3rd

[derik]

I'm workin on a mostly stock '77 280, except msd 43 gph f.pump(noisy bastard). feels electrical. primary coil resistance is .3ohms, secondary is 10.75k, resistor block is 2ohms wires range from 7.99k to 10.20k, plugs are new, cap & rotor look good, pick up set at .3mm. I tried downloading the manual from this site because I don't know the actual acceptable spec range(s).  fuel pressure is 30psi with regulator under full vacuum and 43psi with no vac. I installed an inline filter before the pump and a new factory filter under hood. I even tried bypassing the fuel damper, that just made the pump noise louder. I insulated the pump in the factory bracket by wrapping in rubber to make up diameter, reamed out the mount plate holes under the mount bracket and the mount plate and insulated with 1/8" rubber and o-rings around bolt to prevent metal to metal contact. Still annoyingly loud, any ideas on either? obviously the performance issue is more important. Who wants to be my new buddy??

Derik

[Zed Head]

You said you tried.  Did it work?  Do you have the FSM?

You're kind of rambling around on what the problem is.  There's a lot of "load" that happens before 5000 RPM.  What kind of "stumbling" does it do?  Is there any popping through the intake or is it just a spark problem?  What does the tachometer needle do when it's stumbling?  

The pump noise might be from the filter before the pump, making it too difficult to pull fuel.  Your fuel pressure is higher than spec.  

Not looking for buddies.  Good luck.

[derik]

The engine feels like it's misfiring during hard acceleration(wot), high rpm, 5000 in 1st, 4 in 2nd, and most noticable in 3rd starting around 3100rpm. no popping , just the sound of the engine stuttering from a misfire, like  a plug wire shorting intermittently. the tach needle is steady throughout rpm range. No, I don't have the FSM, no info in my alldata for this vehicle. I am hoping someone familiar with this engine experienced the identical problem.

The only reason for the MSD pump is because the oe was leaking and I needed an affordable fix asap. got a price of$1170 for direct fit. The filter is a spetre glass inline with plastic screen. I am most likely going get send the original out and get a reman.

Thanks for your reply

Derik

[Zed Head]

These old EFI systems tend to run lean once you get all the bugs worked out, ofent it's so bad that you'll get popping back through the intake.  I have a method of richening the mixture and I can get a misfire/stumble if I have it set too lean.  You could try it, it's pretty easy.

http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

The electronic ignition modules fail also but that problem tends to be more obvious than what you're describing.  I'd try the the "fuel tweak" first.  I have mine mounted in the cabin so I can tune it to the finest level.  It makes a difference.

[derik]

That sounds like a simple and cheap enough fix. I'll let you know how it works out. Thanks for the help Zed Head.

Derik

[siteunseen]

I chased the "lean stumble" for a month after a complete rebuild and all new fuel system.  Probably spent $2,000 and my car would spit and buck like crazy.  A friend of mine clamped off the return fuel line to the tank, it ran much better so I put the potentiometer inline and in cabin like Zed Head says.  Finally have the newish running car I worked so hard on.

If your's has the high PSI you posted your under hood fuel lines should be as hard as a rock.  I would pull the hose off the fuel filter and run the pump into a catch can just to see how the pressure and volume are.  Sounds to me more like clogged fuel injectors.  Anyway, good luck.

This might be worth reading too, "quieting a noisy pump",  http://atlanticz.ca/zclub/techtips/fuelpump/index.html

A cheaper pump option, http://atlanticz.ca/zclub/techtips/fuelpump/upgrade/index.html

Here's the whole EFI page, there's a lot on here that will be helpful, most of this is done to a '77 too.  http://atlanticz.ca/zclub/techtips/EFI&fuel.htm

I bought one of the last OE Bosh's, I guess, for about $250 5 years ago.  haven't seen another one anywhere online since.  Now they are all Beck Arnley.

https://www.google.com/search?q=Beck+Arnley+152-0253+Fuel+Pump+-+Electric&rlz=1C1BOFA_enUS494US494&oq=Beck+Arnley+152-0253+Fuel+Pump+-+Electric&aqs=chrome..69i57j69i60&sourceid=chrome&ie=UTF-8

[siteunseen]

Another thing I forgot to mention.  The '77s had a recall for the EGR coupler to the intake manifold.  Mine was never corrected and caused the aluminum intake to rot out all around that thing over the years, HUGE vacuum leak.  You can take a mirror see under the back end and underside of the intake where the EGR connects to the intake.

[sweatybetty]

On 11/9/2016 at 3:11 PM, Zed Head said:

 Not looking for buddies.  Good luck.