A stumble problem

K

ken-r-mer

Senior Member
I'm experiencing a stumble by what appears to be an intermittent electrical short when accelerating between the rpm ranges of 1800 and 2000. My theory: as I accelerate I occasionally hear the radio or a cd hesitate ever so briefly thru the 1800-2000 rpm range enough to cause a CD song to be interrupted. My thinking is the brief electrical short affects the fuel pump enough to cause the A/F ratio to jump, which it does when viewing A/F numbers on the laptop in the garage, under no load. So I'm assuming the electric fuel pump is also affected causing the Air/Fuel mixture to rise ever so briefly from 14-15 up to 17-18 in.-Hg. From idle to 1800 rpm smooth acceleration, 2000 on up to 4000 rpm, smooth acceleration.


My setup: '35 Ford 5 Window Coupe, late model Flathead V8, 12 volt system, 100A alternator, 2 – 1988 Ford Escort TBI's, Megasquirt II V2.2, Mallory Unilite distributor, Mallory coil, Mallory Hyfire 6A Microprocesser controlled CD ignition, electric fan, radio/cd player, T-5 manual trans.


I THINK it all started at the end of last summer when I got caught in a rain downpour about 1 mile from home with no hood on the engine. When I got home, I wiped everything down. The next day I noticed no power and realized the system 50A fuse had blown at the battery. So with everything having a chance to dry off overnight, I replaced the fuse and it started right up.



So far, I've: verified solid tight grounds, had the alternator load tested at a shop, new fuel pump, 12v battery tests ok at rest and overnight holds its charge (thinking of having it load tested at the local parts store), replaced the Unilite module, inspected the advance springs below the module, replaced the coil, inspected the distributor cap for cracks, replaced spark plugs and wires, replaced the wide band O2 sensor, checked for loose wiring at the fuse box, replaced the injectors, cleaned the pin connectors at the TBI's, disconnected the wiring to the Classic gauges (tach, voltage meter, oil pressure in case there is a short in the gauges), cleaned the pins to the Megasquirt ECU, replaced the vacuum line to the MAP sensor,…all with no change. I turned the fan, radio, and lights off…no change, I even removed the three associated fuses… no change.
I'm running out of ideas...after I take the battery to be load tested. Arrrrgh!


Ken
 
Yes, I did, got them thru MSD.
One thing I looked at this morning were the advance springs. The one Bubba did for me for a stock flathead V8 in my F1 were a blue (medium gauge and a fine gauge unpainted) springs. The ones in the '35, built by the previous owner, are a yellow heavy gauge and a blue medium gauge. Think the rate of advance could cause the stumble?
 
Oh, the cam in the '35 is an Isky 77B, and Edelbrock aluminum heads (slightly higher compression than the stock heads) and the block was bored out to 254 cu.in w/ a stock 3 3/4" stroke. Was thinking of swapping out the springs and see what happens.
 
If you had left it as Henry built it, you wouldn't be having this problem. LOL (The devil made me do it.)
 
But the EFI's ($100 each, out of a parts yard) have been leak free, and trouble free for over 4 years, unlike the old Strombergs I had. Just got tired of constantly cleaning the carb bodies and intake 2-3 times a season. And just like my manifold, and TBI's, my hands stay clean too, since tuning is done by laptop.
 
If there was some way to hide EFI inside a Stromberg 97, I would be tempted. Maybe hide the wires inside the choke cable?
 
Maybe try running it with the alternator disconnected? I'd also check the bearings in the distributor. Is the tach signal coming from the distributor?
 
Lawson Cox said:
If you had left it as Henry built it, you wouldn't be having this problem. LOL (The devil made me do it.)
Click to expand...

I agree. This thread is getting waaaaay off-topic. To the O/P : This is a board for stock (and maybe a little modifications on original engines). If you want some help, there are much better boards than this. Good luck on your quest to get your EFI working.
 
https://www.youtube.com/watch?v=SjJYNZirQCU

1242698526_3.jpg


Have nothing for you. Maybe check shield wires... but it worked before.
 
I had a similar situation about 10 years or so back.
Without boring you with all the details, it turned out to be a broken breaker-plate ground strap. This connected on the bottom side of the breaker plate and then to the side ofthe distributor (also underneath the breaker plate). The breaker plate was then trying to do all of its grounding through the pivot stud and was intermittently just breaking contact.
I've since worked on a half dozen or so other cars with similar issues. A couple had no ground strap at all, but you could see where they had been connected at one time.
 
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