bad pressure regulator?

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wpinnix
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bad pressure regulator?

Post by wpinnix » Wed Dec 26, 2012 5:08 pm

I have a 77 bus, stock except for pertronix ignition. I was having issues with cold start idle, bucking or hesitation at mid-rpms, and decreasing fuel economy over the last year. I drive it about once a month not my daily driver, except now I'm driving daily because I'm waiting for a new head for my vw pickup. So, I replaced spark plugs and wires, cap and rotor, air and fuel filters, vacuum lines, and ensured timing is spot on and good advance.I removed the auxiliary air valve and cleaned and adjusted. Temp 2 was out of spec, so I replaced it. All new fuel and vapor lines about 5 years ago; had injectors serviced at the same time and put new Injector seals on.

My afm had worn thru tracks about mid way through the sweep, so rolled the contacts to get them in good clean black. Adjusted per instructions on this forum.

It now idles perfectly when cold and drops to spec in a few minutes. It is running more smoothly, but I still get occasional bucking.

The fuel pressure reads about 30 at idle (not the best gauge, so might be off by a couple of psi) climbs to 36 when vacuum removed from pressure regulator, doesn't seem to return to 30 quickly when vacuum restored, but eventually gets there. Spikes to 60 with return line pinch. Holds pressure when engine stopped.....30 psi after 30 minutes. But, when I apply vacuum to pressure regulator with engine off, pressure does not drop at rails.

I'm thinking the pressure regulator is bad but wanted to get others opinions.

Thanks, Bill

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Amskeptic
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Re: bad pressure regulator?

Post by Amskeptic » Thu Dec 27, 2012 4:36 pm

wpinnix wrote:I have a 77 bus, stock except for pertronix ignition. I was having issues with cold start idle, bucking or hesitation at mid-rpms, and decreasing fuel economy over the last year. I drive it about once a month not my daily driver, except now I'm driving daily because I'm waiting for a new head for my vw pickup. So, I replaced spark plugs and wires, cap and rotor, air and fuel filters, vacuum lines, and ensured timing is spot on and good advance.I removed the auxiliary air valve and cleaned and adjusted. Temp 2 was out of spec, so I replaced it. All new fuel and vapor lines about 5 years ago; had injectors serviced at the same time and put new Injector seals on.

My afm had worn thru tracks about mid way through the sweep, so rolled the contacts to get them in good clean black. Adjusted per instructions on this forum.

It now idles perfectly when cold and drops to spec in a few minutes. It is running more smoothly, but I still get occasional bucking.

The fuel pressure reads about 30 at idle (not the best gauge, so might be off by a couple of psi) climbs to 36 when vacuum removed from pressure regulator, doesn't seem to return to 30 quickly when vacuum restored, but eventually gets there. Spikes to 60 with return line pinch. Holds pressure when engine stopped.....30 psi after 30 minutes. But, when I apply vacuum to pressure regulator with engine off, pressure does not drop at rails.

I'm thinking the pressure regulator is bad but wanted to get others opinions.

Thanks, Bill
How much vacuum are you applying to the regulator when the engine is off?
Engine idle vacuum of 15in is a strong suction for a human to mimic.

I think you might have a leak in the vacuum diaphragm, but you would know that when you applied vacuum to the nipple to see if it holds. You know that holding fuel pressure after shutoff is a different component, right? The spring and ball/seat look to be in good condition if it is holding fuel pressure.

Any vacuum leak would only increase fuel pressure. If you have a bucking symptom, it would suggest a perhaps slightly rich condition. Try leaning out with a simple temporary 4 clicks lean on the black cog. Report back with results.
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

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wpinnix
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Re: bad pressure regulator?

Post by wpinnix » Thu Dec 27, 2012 7:13 pm

Thanks Colin,

I applied 25psi of vacuum with a hand pump....the vacuum held for a couple minutes. I noticed today after parking on a hill that I had difficulty getting enough power to leave my parking spot. Maybe something in the tank? I've been meaning to install my new fuel level sender and filler boot so have begun the process of pulling the tank. I did that seven years ago and did the sealing process re rat well, so not expecting to find much unless the sealer has failed. I cut open the old fuel filter and it was clean....

I have a five day weekend so going to tackle it. One it gets back together if I don't find anything in the tank I'll do the temporary leaning that you suggest.

I will keep you advised, Bill

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SlowLane
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Re: bad pressure regulator?

Post by SlowLane » Thu Dec 27, 2012 9:29 pm

wpinnix wrote: I applied 25psi of vacuum with a hand pump....the vacuum held for a couple minutes.
<pedantic> 25 psi of vacuum is, honestly, impossible, at least on this planet. I expect you're meaning 25" Hg of vacuum. </pedantic>
Sorry, can't help myself sometimes. If your pump has a good seal on the regulator and isn't attached to anything else, the vacuum should hold indefinitely. If it's bleeding off after a couple minutes, then I'd suggest replacing the regulator.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

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wpinnix
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Re: bad pressure regulator?

Post by wpinnix » Thu Dec 27, 2012 10:37 pm

My mistake, yes 25 inches of mercury, not psi. My suspicion is the regulator is bad, since putting vacuum to the regulator when engine not running didn't drop the pressure in the rails. Also, when I rev it to 3000 rpm there is no increase in pressure at the rails stays steady around 30 psi.

Thanks for the input, Bill

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SlowLane
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Re: bad pressure regulator?

Post by SlowLane » Thu Dec 27, 2012 10:49 pm

wpinnix wrote:My suspicion is the regulator is bad, since putting vacuum to the regulator when engine not running didn't drop the pressure in the rails. Also, when I rev it to 3000 rpm there is no increase in pressure at the rails stays steady around 30 psi.
I'd say you've accumulated sufficient evidence to make the regulator your prime suspect.

When monitoring the effect of revving the engine on fuel pressure, it's very instructive to have a vacuum gauge teed into the line controlling the regulator. That way you can watch the vacuum and fuel pressure simultaneously. The fuel pressure fluctuations should track the vacuum signal pretty much exactly.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

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wpinnix
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Re: bad pressure regulator?

Post by wpinnix » Fri Jan 04, 2013 5:45 pm

OK

So, gas tank was sparkly clean, no problem there. Replaced all fuel lines and vapor return lines...it had only been 5 years, but worth it. Rechecked all valves, timing, etc....everything in spec. Drove for a day and no issues....who hoo.

Next day, issues crept up again. Replaced fuel pressure regulator with known good. Still having bucking or hesitation. In 4th gear at 55, if I back off accelerator slightly (still putting load, but less throttle), it hesitates or bucks. Acclerating through 30 mph in 3rd gear, it bucks and hesitates. At full throttle, at higher rpms, I have no problem, just have issues in the preceding situations (at least it is most repeatable in those situations)

So, moved black cog 4 clicks to lean....as Colin suggested still having issues. There is now a delay in coming down from higher rpms....I assume because tension is reduced. But, when I tested AFM (before moving black cog) I showed slightly lean at idle and slightly lean at 2900 rpm so I don't think it is running too rich. I moved static adjustment 1 click rich, slightly better at 2900....moved one more click, higher rpms spot on. Idle went pretty high, bottomed out idle adjustment at 1000 rpm, used afm 'c' to get idle down to 950. When I check afm idle, I still get a 'lean' reaction, even though I'm pretty sure it's on the rich side (due to bottoming out of idle adjustment screw on throttle body). The bus seems to perform better, smoother at higher rpms and better throttle response.

ANYWAY, I'm a little stumped. So....(I don't know why I didn't do it before) I checked the AFM terminals as per Bentley. Temp Sensor 1 was 2350 ohms. Terminals 6-9 were 280 ohms. Terminals 7-8 were 625! Could this be the source of my problem? What do those terminals do and how would it affect the performance of the fuel injection system?

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Amskeptic
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Re: bad pressure regulator?

Post by Amskeptic » Sat Jan 05, 2013 12:29 pm

wpinnix wrote: Temp Sensor 1 was 2350 ohms.
Terminals 6-9 were 280 ohms.
Terminals 7-8 were 625!
What do those terminals do and how would it affect the performance of the fuel injection system?
6-9 and 7-8 are potentiometer terminals, Get a fine piece of 1000 grit sandpaper under the wiper with the grit side up paper side down and rub wiper back and forth about a half an inch one or two times. Remove sand paper and clean contact ends with a paper towel. The top of the wiper has a copper "brush" that meets the copper contact piece that goes to the terminal block. You can do a continuity test while gently pressing down on that contact piece, just to see if there is a change in continuity. Have you established, under bright light, that there is no "wear-through" on the black track?
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

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wpinnix
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Re: bad pressure regulator?

Post by wpinnix » Sat Jan 05, 2013 12:56 pm

I 'rolled' the contacts to get them into clean black as the previous tracks were worn through. I tried to get the board to move but couldn't budge two of the screws so no luck there.

I will try cleaning the wipers as you suggested, get it warmed up by taking it for a drive and report back if I've changed the continuity at the terminals.

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wpinnix
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Re: bad pressure regulator?

Post by wpinnix » Sat Jan 05, 2013 4:32 pm

I used the sandpaper on the contacts and took for a drive.....success, no hiccups no bucking! But I'm not claiming victory yet....I had a day with no problems last week and then the next day they came back.

So I tested the continuity on the AFM terminals after I got back from the test drive. I broke out my AFC manual that I downloaded a number of years ago and the specs are different than what the Bentley manual says....anyway I digress. So my measurements were:

6 & 9 = 280 (in spec)
6 & 8 = 180 (in spec)
8 & 9 = 100 (in spec)
6 & 7 = 820 (not in spec)
7 & 8 = 835 (not in spec)
6 & 27 = 2540 (in spec)

So, I'm realizing that those wipers are darn sensitive, that my issue was with terminal 7 which is the one that connects to that big copper bar that goes to the top of the wiper. When I pushed down on the terminal seven contact to top of wiper, the ohms increased to 843 or so...strange...so I ran the sandpaper over those contacts...brought it down to 745 or so...better, but still out of spec. So I gently pushed down on the wiper contacts...inside wiper, no change, outside wiper...ohms dropped to 440! So I wasn't getting quite a good contact with that outside one. I used my wifes awesome little jewelry pliers to make super subtle adjustments to the wiper arms until I got it so settle at 430 (out of spec for bentley, but in spec according to afc manual). So now my numbers that changed are:

6 & 7 = 350 (out of spec...afc says 40-300)
7 & 8 = 430 (in spec according to afc 100-500)

Took it for another drive and again, no hiccups, no bucking, no hesitation. And, since I've adjusted the afm it's running way better than it has in the last couple of years. I'll give it another week of driving before I claim victory.

So, what I learned.....a LOT about the afm, especially those wipers and contacts and their sensitivity to changes. Also, I think I'll invest in another AFM...realizing the sensitivity of the one I have and that the specs are borderline, it would be nice insurance to have a spare just in case. Now I feel confident about making adjustments....I have the skills to get a 'new' one into shape.

I believe the problems i've had have all been related to the AFM. I previously had lots of bucking through the midrange of the sweep, coinciding with where the board was worn out. When I rolled the wipers, it cured 90% of the problem. I forgot to mention, that before I did the sandpaper, ohms were 650 and there was a spike to 1300 right in the middle of the board adjacent to my old worn out tracks.....my theory is this is the spot where I was getting the recent hiccups (accelerating through 30 mph, and coming off accelerator at 55 mph). Since re-tensioning the contacts, I've eliminated this spike in the middle and brought the resting ohms down into spec. So, that's my theory, lets see if it stays running fine...I think it will.

Thanks Colin and SlowLane....awesome advice!

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Amskeptic
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Re: bad pressure regulator?

Post by Amskeptic » Sat Jan 05, 2013 7:22 pm

wpinnix wrote:
Thanks Colin and SlowLane....awesome advice!
Very diplomatic of you, but I think you narrowed it down.
Chime in on satchmo's thread "cutting out" in trouble-shooting forum. He might find your experiences helpful.
ColinCongratulations. . .SoFar
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
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Re: bad pressure regulator?

Post by luftvagon » Sun Jan 06, 2013 8:13 am

Good luck finding a good and in working order AFM. May want to save those pennies for *squirt conversion.
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

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