Bad Fuel Pressure Sensor? Or bad main fuel pump?

[Skid]

I agree with Tom. I had this same issue with an oil pressure sensor. I added a ground wire, just like Tom stated, and the problem went away.

[Saville]

Thanks everyone for all the comments. Really very helpful.

Ok so I think what I'll do is progressively more complex tests starting with:

1) Tom Martin's suggestions of an alternate Ground using a hose clamp

If that fixes it then the permanent solution would be to unscrew the sensor from the bock, clean the threads, and re-attach?



If that doesn't fix it then:

2) Tom Swearengen's (and others) of testing with a mechanical pressure gauge.


My plan would be to plumb in a T fitting then hook one output back to the fuel sensor. The other output through a couple feet of hose to the mechanical gauge.

I have a couple questions on that:

- Will all that plumbing still be properly pressurized so that I get accurate readings?

- Can anyone recommend a good mechanical gauge?

- would the gauge first have to be calibrated?



I suppose I could just forego the T fitting and hook up a mechanical gauge, temporarily, for the test. But I would feel better if I saw the gauge reading pressure but the EFIS showing the "---". That way I would know the mech fuel pump is fine and the issue is somewhere between (and including) the sensor on down to the EFIS.

Any comments/criticisms of the plan are welcome.

[TS Flightlines]

Actually---if you wanted to keep the existing setup, AND tee in a mech gauge---that would cross test BOTH systems at the same time, inflight. So---if you get a low press indication on the EFIS, and the Mech guage is normal----that would indicate to me that we have a electrical issue, either sender, connections, or maybe even a software issue, but thats really doubtful. BOTH if both the EFIS and the gauge read the same, then its an actual pressure failure.
Then you can start looking at pump, hoses, fittings, etc.

Seems like alot of work and testing, but I know of a builder that paid alot of money for parts, and needed to replace a crimp connector at the sender.
Tom

[Saville]

Originally Posted by TS Flightlines

Actually---if you wanted to keep the existing setup, AND tee in a mech gauge---that would cross test BOTH systems at the same time, inflight. So---if you get a low press indication on the EFIS, and the Mech guage is normal----that would indicate to me that we have a electrical issue, either sender, connections, or maybe even a software issue, but thats really doubtful. BOTH if both the EFIS and the gauge read the same, then its an actual pressure failure.
Then you can start looking at pump, hoses, fittings, etc.

Seems like alot of work and testing, but I know of a builder that paid alot of money for parts, and needed to replace a crimp connector at the sender.
Tom

I'd rather test a lot and pin down the exact issue before I start spending a lot of money on replacing parts.....and/or pulling the engine.

To TEE in a mech gauge I would need to:

1) identify the T fitting I need to get.

2) Identify the bulkhead passthrough I need to get.

3) Identify the pressure lines I need to get.

4) Pick the pressure gauge. I have an unused 2.25" hole in the instrument panel that I could use for that purpose

Lots of research to do.

[Sam Buchanan]

Or you could just replace the mechanical fuel pump. Those things have a finite life span and I suspect this will cure your low fuel pressure. I had the same issue and the new pump brought everything back to normal.

If in the off chance the new pump doesn't fix the problem, you will then have a spare pump on the shelf.

[SMRacer]

Since you have observed the errant readings on the ground (at your 1800 RPM runup), I see no reason to run a mechanical gage in a semi-permanent install through the firewall.

You can tee into the sender with a mechanical gage, and then with the cowling off have an observer watch the mechanical gage during your start-up, idle, and run-up. If you have a significant difference between the mechanical gage and the EFIS, then you probably have enough information to resolve the problem.

If you are uncomfortable with having an observer in proximity to a rotating propeller, then you can run a short hose from the tee to the gage so that it is visible from the cockpit.

[Saville]

Originally Posted by SMRacer

Since you have observed the errant readings on the ground (at your 1800 RPM runup), I see no reason to run a mechanical gage in a semi-permanent install through the firewall.

You can tee into the sender with a mechanical gage, and then with the cowling off have an observer watch the mechanical gage during your start-up, idle, and run-up. If you have a significant difference between the mechanical gage and the EFIS, then you probably have enough information to resolve the problem.

If you are uncomfortable with having an observer in proximity to a rotating propeller, then you can run a short hose from the tee to the gage so that it is visible from the cockpit.

That is actually my plan. Go from the NPT plug on the top of the manifold block to a gauge which is visible by me from in the cockpit. Run the plane with the upper cowl off (carefully watching CHT all the time) and note the results.

I would be very uncomfy with an observer near the prop.

[Lenny Iszak]

Unlikely that it's a grounding issue. You have two terminals on that sender, there's no extra ground needed, it's already grounded through one of the terminals. If it was a Stewart Warner type single terminal sender then yes, but looking at your picture that's not the case.
The sender is about $50. You need a spare anyway, if it hasn't quit yet, it will soon. Don't go poking holes in your firewall just yet.
I like Bill's idea to check the sender with a compressor that way you can sweep through the whole pressure range easily. That's how I calibrated mine.

Lenny

[Saville]

Originally Posted by Lenny Iszak

Unlikely that it's a grounding issue. You have two terminals on that sender, there's no extra ground needed, it's already grounded through one of the terminals. If it was a Stewart Warner type single terminal sender then yes, but looking at your picture that's not the case.
The sender is about $50. You need a spare anyway, if it hasn't quit yet, it will soon. Don't go poking holes in your firewall just yet.
I like Bill's idea to check the sender with a compressor that way you can sweep through the whole pressure range easily. That's how I calibrated mine.

Lenny

If the grounding terminal is bad somewhere along the line, the grounding test will reveal that.

I do agree about having a spare sender.

[BillL]

Originally Posted by Lenny Iszak

Unlikely that it's a grounding issue. You have two terminals on that sender, there's no extra ground needed, it's already grounded through one of the terminals. If it was a Stewart Warner type single terminal sender then yes, but looking at your picture that's not the case.
The sender is about $50. You need a spare anyway, if it hasn't quit yet, it will soon. Don't go poking holes in your firewall just yet.
I like Bill's idea to check the sender with a compressor that way you can sweep through the whole pressure range easily. That's how I calibrated mine.

Lenny

Ya can even use a small portable tank.