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Intermittent loss of power
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jeremypbeasley
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Joined: September 18, 2018
Posts: 164
Location: Seattle, WA
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PostPosted: Mon Mar 29, 2021 10:31 am    Post subject: Intermittent loss of power Reply with quote

Howdy there, internet people.

I would love some help trying to solve a problem I'm having with my van!

Symptoms:
- Intermittent loss of power
- Ranges from momentary loss of forward motion (not unlike when you get going too slow in too high a gear) to sounding like you're running out of gas
- Tends to happen more on the highway than in the city
- Seems to occur more often at higher speeds or otherwise high fuel demand.
- Replaced the already noisy fuel pump and filter thinking this was the cause, but it didn't help
- Occasional exhaust pops during and after this occurs.
- Gas mileage is right around 11 mpg

Background:
- 1985 Vanagon GL. 1.9 Swap. Digijet.
- Fuel pump and new filter have been replaced this week. All Bosch good parts with solid new lines and clamps.
- No fuel leakage.
- Unknown fuel pressure (gauge is broken at the moment!)
- No clutch smells or oddness in the pedal.
- Voltage measures good with engine off (12.6) and engine on (13.75+).
- No issue with gas pedal or cable.
- No oil or coolant leaks.
- New muffler/tailpipe is slightly angled too high being somewhat obstructed by the rear body panel. Will adjust today.
- Visually checked all vaccum lines. Everything looks tight and to spec.
- Noticed one small rip in both CV boots on the gearbox side, throwing grease a bit (rockford brand, rebuilt 6 months ago)

Any ideas of what I could investigate here?
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hdenter
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Joined: October 14, 2008
Posts: 2749
Location: San Luis Obispo, CA
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PostPosted: Mon Mar 29, 2021 1:07 pm    Post subject: Re: Intermittent loss of power Reply with quote

Did you crack open the fuel filters to look for rust? You can have rust in your tank preventing flow to the filters.

Have you tested the AFM for continuity through the full sweep of the arm? There could be a dead spot on the track that corresponds with average highway speed and load.

Your fuel economy seems rather low to me. What do your plugs look like when you pull them?
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'84 sunroof vanagon
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Ronzo_volvo_guy
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Joined: December 31, 2015
Posts: 194
Location: Connecticut
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PostPosted: Mon Mar 29, 2021 2:32 pm    Post subject: Re: Intermittent loss of power Reply with quote

Jeremy;

The first thing I thought of as hd, was a fuelfeed interruption, although if that occurs due to tank sediment blocking the Fuel Filter, it is usually fatal (and not intermittent), and doesn't fix itself until FuPu is shut off, some of the particulates blocking the FuFi drop away from filter material to allow starting, and the cycle to repeat.

If you have a Fuel Pressure Gauge (are you sure you didn't mean Fuel Tank Gauge) "Unknown fuel pressure (gauge is broken at the moment!)"...I'd see about getting it working, as fuel delivery pressure is such a critical part of the FI sys, it would be nice to see if there is a correlation between a momentary drop-out and drop in fuel pressure. ...otherwise, Ignition is the next suspect sys (and intermittent failure is more often associated with electrical or Ignsys)...observe Tach when drop-out occurs...does Tach indication drop to zero? I'd also have a preliminary look at Distrib Cap/Rotor to check for anything suspicious...

Intermittents are always a pain to locate...until they fail "hard", and you have something specific to work on, the best you can do is try to correlate their occurrence with other things...like "only does it with under 1/4 Tank", or "only happens on engine braking down a hill" or during left turns... etc.

Good Hunting!
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davlance01
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Joined: May 10, 2013
Posts: 224
Location: Ohio
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PostPosted: Tue Mar 30, 2021 5:40 pm    Post subject: Re: Intermittent loss of power Reply with quote

I had that same issue.
First time it was the thermostat connector.

What was happening was the incorrect fuel trim was pulled from the map in the ecu based on intermittent coolant temperature readings.

Second time it was the ignition switch loosing connection and cutting the power off to the coil.

Third time it was a bootleg bosch fuel pump off of amazon. Correct fuel pressure and flow until under load.

In short...your going to have to break open the digijet/digifont manual and check for the proper values being fed into computer.

If you look for what is wrong instead of what part to buy you will be way further ahead.

If you don't have the skills to diagnose automotive systems it's time you learn or your van will never run right even if you fix this issue.

I started by watching tst seminars on YouTube and purchased a lab scope and stopped asking people what could be wrong. Have you ever heard a mechanic say he wasn't really that good at his job?

Save yourself some time and learn these systems and you'll never worry again about what is wrong with your car.
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