Starvation at higher RPM

Carbs & F.I.

Moderators: Sluggo, Amskeptic

Post Reply
luftvagon
Old School!
Location: Little Rock, AR
Status: Offline

Starvation at higher RPM

Post by luftvagon » Sun Nov 18, 2012 4:41 pm

This just started happening with no changes to the fuel injection and other fuel system. It does not happen very often. Yesterday and today happened well into the ride after the van was fully warm. This was well into 2 hour drive.

The van started having micro-stumbles at higher RPM. It was mostly noticeable in second gear; stopping and starting. It was least noticeable in higher gears.

The AFM is tuned to the edge of lean, as suggested by the procedure. This has not changed. I changed the brake master cylinder recently.

The stumble is not noticeable with no load.
It feels as if the van is not getting enough air or fuel, but there are no pops; or maybe it felt as if the time did not follow the throttle.
The van felt like it had less power, and revved slower.
1981 Volkswagen Vanagon Westfalia - air-cooled Type4 1970cc CV (hydraulic lifters, 42x36 valves, stock cam, microSquirt FI with wasted spark ignition)
1993 Ford F-250 XL LWB Extended Cab 7.3L IDI

User avatar
Amskeptic
IAC "Help Desk"
IAC "Help Desk"
Status: Offline

Re: Starvation at higher RPM

Post by Amskeptic » Wed Nov 21, 2012 7:37 am

luftvagon wrote:This just started happening with no changes to the fuel injection and other fuel system. It does not happen very often. Yesterday and today happened well into the ride after the van was fully warm. This was well into 2 hour drive.

The van started having micro-stumbles at higher RPM. It was mostly noticeable in second gear; stopping and starting. It was least noticeable in higher gears.

The AFM is tuned to the edge of lean, as suggested by the procedure. This has not changed. I changed the brake master cylinder recently.

The stumble is not noticeable with no load.
It feels as if the van is not getting enough air or fuel, but there are no pops; or maybe it felt as if the time did not follow the throttle.
The van felt like it had less power, and revved slower.
Start simple. In any given instant, a vacuum hose can split. Look at the decel valve/fuel pressure regulator circuit and make sure it is OK.

Next, this is a classic warning of a fuel filter/pump that is not quite putting out. A quick road experiment is to get the symptoms to occur. Run back and unplug the vacuum line to the fuel pressure regulator, stick a golf tee or a screw into the vacuum hose. Have symptoms diminished?

Finally, try a slightly richer mixture. I find that these engines do not arrive at full operating temperature until every single piece of sheet metal, every single part with any mass whatsoever, has fully absorbed operating heat. This can take up to a half-hour or more. Your CHT sensor will continue to react by leaning the mixture as overal temps find their homeostasis. I have found that if I do not have a thoroughly warmed engine, my "tuned-to-the-edge-of-lean will tip over into lean.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

luftvagon
Old School!
Location: Little Rock, AR
Status: Offline

Re: Starvation at higher RPM

Post by luftvagon » Wed Nov 21, 2012 8:04 am

Thanks Colin. I suspected it could be the fuel pump. I no longer have the de-acel valve; it was getting in the way.. I have a vacuum hose off the intake plenum going directly into the FPR.
We are going to give all vacuum hoses another look, warm her up, and give her a another AFM and AFR check.... Fuel pump on order. I trashed a brand new pump moving brake fluid through it (speed bleed).
1981 Volkswagen Vanagon Westfalia - air-cooled Type4 1970cc CV (hydraulic lifters, 42x36 valves, stock cam, microSquirt FI with wasted spark ignition)
1993 Ford F-250 XL LWB Extended Cab 7.3L IDI

User avatar
Amskeptic
IAC "Help Desk"
IAC "Help Desk"
Status: Offline

Re: Starvation at higher RPM

Post by Amskeptic » Wed Nov 21, 2012 8:19 am

luftvagon wrote:I trashed a brand new pump moving brake fluid through it (speed bleed).
I know we are in "Fuel Delivery" here, but that sounds intriguing. When, what, why, and how quickly did it get killed?
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

luftvagon
Old School!
Location: Little Rock, AR
Status: Offline

Re: Starvation at higher RPM

Post by luftvagon » Wed Nov 21, 2012 8:50 am

It still runs, sucks and pushes fluids fine. I'm just not sure if I would put it back on a vehicle. I also run it dry for a bit.. 2-3 minutes at the time, pulling brake fluid through the line :)
1981 Volkswagen Vanagon Westfalia - air-cooled Type4 1970cc CV (hydraulic lifters, 42x36 valves, stock cam, microSquirt FI with wasted spark ignition)
1993 Ford F-250 XL LWB Extended Cab 7.3L IDI

luftvagon
Old School!
Location: Little Rock, AR
Status: Offline

Re: Starvation at higher RPM

Post by luftvagon » Wed Nov 21, 2012 12:51 pm

Vacuum hoses check out.
I'm 4 and 1/2 turns on the idle air mixture screw.
On idle, I'm pulling 14.1 AFR, and at 3000 RPM and no load, I am also pulling 14.1 AFR. Dangerously close to lean, should you add load...
1981 Volkswagen Vanagon Westfalia - air-cooled Type4 1970cc CV (hydraulic lifters, 42x36 valves, stock cam, microSquirt FI with wasted spark ignition)
1993 Ford F-250 XL LWB Extended Cab 7.3L IDI

User avatar
Amskeptic
IAC "Help Desk"
IAC "Help Desk"
Status: Offline

Re: Starvation at higher RPM

Post by Amskeptic » Wed Nov 21, 2012 6:54 pm

luftvagon wrote:Vacuum hoses check out.
I'm 4 and 1/2 turns on the idle air mixture screw.
On idle, I'm pulling 14.1 AFR, and at 3000 RPM and no load, I am also pulling 14.1 AFR. Dangerously close to lean, should you add load...
"Dangerous" is too histrionic a word for any no-load reading. You know that the wiper reacts instantly to subtle increases in air flow, I can and do run 16:1 up to 23:1 at no load overrun, and it dives to 11.9 upon acceleration, where it matters. Do you have misbehavior at light loads or at transition from no to heavy load?
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

luftvagon
Old School!
Location: Little Rock, AR
Status: Offline

Re: Starvation at higher RPM

Post by luftvagon » Wed Nov 21, 2012 7:34 pm

slight hesitation... 14.1 is also steady state cruise...
1981 Volkswagen Vanagon Westfalia - air-cooled Type4 1970cc CV (hydraulic lifters, 42x36 valves, stock cam, microSquirt FI with wasted spark ignition)
1993 Ford F-250 XL LWB Extended Cab 7.3L IDI

luftvagon
Old School!
Location: Little Rock, AR
Status: Offline

Re: Starvation at higher RPM

Post by luftvagon » Thu Nov 22, 2012 11:37 am

*** SOLVED ***
The timing adjustment lock-ring got loose. Timing was slowly advancing, and making things worse and worse. The dead give-away was oil under the distributor. I barely touched it, and off she went.
I got the van re-tuned again. This time I got it on the money...

The range (as referred to dynamic adjustment in the AFR procedure) was adjusted to give me 13.5 AFR at steady cruise at 3000 RPM.
The throttle enrichment gives me close to 11.7, with a hint of black smoke. Range could be tightened up a bit.
The idle is set to 14.7 AFR... So far so good. According to the procedure, I am on the money, just where the motor likes it. Moving the wiper in either direction doesn't slow or speed up the motor.

Score!! Now for a 30 minute test run.
1981 Volkswagen Vanagon Westfalia - air-cooled Type4 1970cc CV (hydraulic lifters, 42x36 valves, stock cam, microSquirt FI with wasted spark ignition)
1993 Ford F-250 XL LWB Extended Cab 7.3L IDI

User avatar
Amskeptic
IAC "Help Desk"
IAC "Help Desk"
Status: Offline

Re: Starvation at higher RPM

Post by Amskeptic » Fri Nov 23, 2012 8:47 am

luftvagon wrote: *** SOLVED ***
on the money...
So far so good.
Score!!

Now for a 30 minute test run.
Make it an hour and you can make a quickie fuel mileage test of it. 16-18 mpg is good. 22 is too lean. 11 mpg suggests a tad rich.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

Post Reply