Tricky fuel delivery problem-please help!

[72westie]

Hello friends! My 1979 2.0 FI motor has a strange fuel problem. If the gas is less than half a tank it will sputter and die out under load up a hill or any WOT for example (stays running but takes a nose dive). It will drive at half throttle in a higher gear if I'm ginger with it. When it really gets bad, if I shut off the car and immediately start it back up again (2-3 seconds), the car runs fine.

Fuel pump? Vapor lock? Idk but its really shorting my drive distance.

Also to be fair, my gas gauge is weak. At a full tank the gauge reads 1/2. But between 1/4 and R it starts to buck. I had the sender replaced last year but maybe it was a bad unit or something. It seems the fuel pickup should be good though as my mechanic was in there.

I don't know anything about FI but I love having it! I've replaced the fuel pump twice. The second time I opted for the more pricey Bosch unit. Doesn't sound noisy usually but sometimes I can hear it.

Thanks so much!
Kyle
Sarandë, Albania

[cmonSTART]

There should be a place to hook up a fuel pressure gauge on the 3/4 side fuel rail. I'm curious to see what it's reading normally and when you have problems.

Is your FI complete/stock?
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'78 Bus 2.0FI
de K1IGS

[SGKent]

when did you last replace your fuel filter?

Are you determining full and 1/2 off the gauge or off filling the tank to where it won't take more, and counting mileage. When it starts to buck you could be near empty. See how many gallons it takes from 1/4 full, to full.
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[busdaddy]

My first guess is there's some sort of debris in the tank that blocks the outlet momentarily, know anybody with a snake like inspection camera?
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[SGKent]

[my59]

Change the fuel filter, yeah that cube shaped one.
I added a gas rated shut off valve upstream the first time I did it to make future changes less messy.
Is it tuned, valves adjusted, points set, plugs gapped, timing set?
Ignore the fuel gauge. Keep a record of gas in, odometer reading, and do the math.
You can get a fuel pressure gauge cheap and build the fittings to screw into the FI at a hardware store.
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my59: Well son, my grandfather died before I got to drive it, so does that answer your question?
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[Wildthings]

Does your FI system use an O2 sensor? If so perhaps your problem is O2 sensor related.

[72westie]

Thanks so much for the quick responses. I have not changed the fuel filter. It is not a California model, but is stock in all its forms except exhaust. I'm not sure about O2 sensor but it does have EGR (retrofitted into an Empi style header because the OG exhaust was not available re-pop and I was in CA and had to fit a cat as well)

The fuel pressure monitoring is a good idea and I do have tools and gauges but unfortunately they are buried in storage and not accessible now. However maybe I can pick up a cheap one or borrow one. I moved to the far away country of Albania and there aren't many tools or stores available here. I have a snake cam too but thats also buried! But I don't think its for liquids anyway.

Points were recently replaced and the valves should be good as well (hydraulic). Runs great except for this problem. Winds up and pulls nicely. Dunno the mileage of the motor but it had a piston and head rebuild about 4 years ago.

As far as the gauge, it never reads full. I always fill up as much as the gas pump will allow. So far I have not been watching mileage but can do over the next few days. Just topped off yesterday. I have wondered if there is some reason the gas pump thinks the tank is full when it is not. Like, is there some sort of blocked vent or something. Where I live now the pumps do not have the emissions collar on the pump handle.

For the pressure measurement, does it matter where in the line I tap in so long as its after the filter?

Thanks again for all your suggestions!
Kyle

[SGKent]

[Randy in Maine]

When you get the old filter out, cut it open with a utility knife and see if it is full of rust particles.

Make sure you own something like this. Handy for all sorts of troubleshooting including replacing the fuel filter..

https://am-ebay-images-items.s3.amazonaws.com/item/AM-628398464.jpg

[SlowLane]

Also check that your EVAP system isn't plugged somewhere, causing a partial vacuum to build up in the fuel tank as the fuel level drops. A hint that this is happening is if you get a brief sucking sound when you remove the fuel cap to fill up.
I encountered this when going through the process of sealing up my EVAP system in preparation for CA smog check. Turns out that the inlet in my charcoal canister from the fuel tank was clogged up solid, preventing the tank from venting altogether.
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[my59]

[72westie]

Thanks for the leads. I'll get a filter and see if I can find a gauge this week. It'll be a while before I can repost. Thanks again for your help.

[72westie]

Thanks for the archives, my59. The AFC manual is great. I think its better, or seems easier than the factory shop manual.

Kyle