Hmmm, loss of power won't hold speed...

classic Classic list List threaded Threaded
58 messages Options
123
Reply | Threaded
Open this post in threaded view
|

Hmmm, loss of power won't hold speed...

reamer
I usually don't drive on the highway, but the car show was 28 miles away, Soooooo, on the highway flat road holding 75mph, up hill losing speed, down shifting to 4th, still losing speed, Step on it and boy the growling noise under the hood IS impressive but still losing speed, What the H***!

Regular street driving seems fine, but again stepping on it, Great "toilet flushing" noise, but no increase in speed!

Yet and a stop sign, it will chirp from a dead stop, (rules out clutch)

So, back in the bat-cave I investigate....


4 year old Edelbrock 1406? Non EGR 4-v and intake. No visual leaks stains.

15 inches vacuum, 10 BTC (with vac advance plugged)

Pulled all the plugs, while all out, did a compression test, 145 to 150 psi throughout.

Installed new Autolite plugs, gapped to 44.

Thought the rubber fuel line might have been collapsing, Sooo bent up a new 1/4" brake line.

6 psi of pressure on 4 year old mechanical fuel pump.


Head down the road, just as crappy as before, 40 mph and step on it, lots of deep growling but no increase, actually decrease in speed....

Just for fun, swapped out modules, same result.
Thoughts?
1986 F-150 Flareside 4x4, 351, 4-v, ZF5 speed. AC, Cruise, Tilt, Slider, Digital clock, Radio, Lariat seat, Pwr doors/locks
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

Rembrant
You didn't mention the fuel filter...I assume you changed it?

What about the fuel tank and sending unit? Have they been replaced?...Maybe the "sock" on the sender is plugged up?

I know, I'm not much help...
1994 F150 4x2 Flareside. 5.0 w/MAF, 4R70W, stock.
1984 F150 4X2 Flareside. Mild 302 w/ 5spd. Sold.
1980 F150 4X4 Flareside. 300i6 w/ 5spd. Sold in 2021.
1980 F100 4X2 Flareside. 351w/2bbl w/NP435. Sold in 1995

Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

ArdWrknTrk
Administrator
In reply to this post by reamer
Lack of volume, not pressure?

Something amiss with the secondaries?
Links, interlocks, hanging butterflies???
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

reamer
Yes new inline filter too, My Brother mentioned going to a 3/8" (minimum) ID fuel line but the original line from the tank is only 1/4" and the fuel pump won't take 3/8"

Tank and pick-up are @6 years old....
1986 F-150 Flareside 4x4, 351, 4-v, ZF5 speed. AC, Cruise, Tilt, Slider, Digital clock, Radio, Lariat seat, Pwr doors/locks
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

grumpin
In reply to this post by ArdWrknTrk
I’m still suspicious of the clutch. Or an intake leak.
Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

ArdWrknTrk
Administrator
This post was updated on .
Intake leak would have been my guess, but he doesn't mention any other symptom like high idle.
Slipping clutch would show on the tach.
EGR leak would sound that way at cruise, but he said it just gets louder if he floors it.

Clogged catalytic converter fits the symptoms.
Is there anything left of the A.I.R. thermactor system left on this truck?

3/8 feed and 5/16 return seem standard on any Ford I've ever seen.

1/4" is a -4AN hose, 3/8 = -6AN, etc...
I'm having a hard time finding flow rates for 1/4" at any pressure, let alone 6 psig.
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

reamer
Idles at 600 650, nothing left to the emissions, Eddy intake is a non-EGR, ran great for a few years, Three years ago did the ZF swap new hydraulics, slave , master, clutch.
 Idles fine.
Tach. is steady, no jumping....
Still a clean top end no oil or coolant leaks.....
Don't remember if it still has a catalytic converter.... will have to look
1986 F-150 Flareside 4x4, 351, 4-v, ZF5 speed. AC, Cruise, Tilt, Slider, Digital clock, Radio, Lariat seat, Pwr doors/locks
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

ArdWrknTrk
Administrator
I would definitely give a look for a clogged exhaust.
You have all the symptoms.

Just for giggles, unbolt the front of the muffler (or Cat if you have one)
and take it for a spin.

15" Hg is pointing at a clog too.
Stock should have 20+, and it takes a pretty healthy cam to put you at 15.
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

reamer
Well did more testing, At idle (600 ish is smooth) look down the carb no dripping at idle..
did the Cat "snap" test, says that snap to WOT, vacuum should drop only for a second and recover almost instantly (if not clogged) and it does this.

Did second Cat test, Hold at 2500 rpm, if vacuum steadily drops over time, its clogged, this comes right back to 15 and over time looks to be increasing to 16 inches.
Runs great standing still...


Timed to 10 BTDC, (with vac advance hose plugged) but wondering if timing goes out the window, with an acceleration load....
1986 F-150 Flareside 4x4, 351, 4-v, ZF5 speed. AC, Cruise, Tilt, Slider, Digital clock, Radio, Lariat seat, Pwr doors/locks
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

ArdWrknTrk
Administrator

Standing still,.     but not under load.
That's why I said secondaries....
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

1986F150Six
Administrator
Is it possible that the mechanical timing advance is not working properly?
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

reamer
Seems to pass the Cat tests, appears to be breathing well, what is going in appears to be going out.... I don't know how old the engine is, or if any work done to timing chain/water pump.
1986 F-150 Flareside 4x4, 351, 4-v, ZF5 speed. AC, Cruise, Tilt, Slider, Digital clock, Radio, Lariat seat, Pwr doors/locks
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

ArdWrknTrk
Administrator
Might be interesting to throw a light on it and see where the marks are in relation to the#1 event.

When my plastic gear wore out it was spitting back through the carb anytime I accelerated.
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

reamer
Explain? Timing light shows 10 BTDC, firing off #1 plug.  is there something else I can do?
1986 F-150 Flareside 4x4, 351, 4-v, ZF5 speed. AC, Cruise, Tilt, Slider, Digital clock, Radio, Lariat seat, Pwr doors/locks
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

ArdWrknTrk
Administrator
If the chain skipped the crank and cam (that drives the distributor) would not be synced.

Your timing would be way retarded.

David had a good idea.
Does the timing advance with rpm's?
Up to about 3k..
How about the vacuum?
What's the timing with it connected?
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

1986F150Six
Administrator
This post was updated on .
If you do not feel comfortable checking the advance curve vs. engine speed, try setting the initial timing @ 14 or 15 degrees BTDC. It might be harder to start, but once it does, go for a test drive and see if any different than before [10 degrees BTDC].
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

reamer
So if I pulled the water pump and timing cover right now, IF it is in correct position, (nothing skipped) the small indicator divots in the crank and cam should still be in 6 o clock on the top one and 12 o clock on the bottom one correct? If it skipped they would not line up with a straight rule?

Thanks
Ron
1986 F-150 Flareside 4x4, 351, 4-v, ZF5 speed. AC, Cruise, Tilt, Slider, Digital clock, Radio, Lariat seat, Pwr doors/locks
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

ArdWrknTrk
Administrator
Why would you even go there?  (Where I am right now)

If you want to know how much slop is in your timing chain just get a 15/16 socket and a breaker bar.
Pull off the distributor cap and rock the crank back and forth.

If you move the crank 5* or more before the rotor reverses direction it's SHOT.
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

reamer
5 Degrees, correct?
1986 F-150 Flareside 4x4, 351, 4-v, ZF5 speed. AC, Cruise, Tilt, Slider, Digital clock, Radio, Lariat seat, Pwr doors/locks
Reply | Threaded
Open this post in threaded view
|

Re: Hmmm, loss of power won't hold speed...

ArdWrknTrk
Administrator
This post was updated on .
More or less.

That's about the most slop you'll get before it starts skipping.
*** if you still have a plastic cam gear.
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.
123