Fuel pressure jumping all around...SPA F/P guage

[Motorhead]

I put in some new SPA's a month ago. It seems that the fuel pressure readings are a bit jumpy. It will read 16psi then 9. I have replaced the lift pump and filter. There isn't a restricter on the sending unit.

Anyone with SPA's have the same result???

 

[barryg41]

Have you tried to increase the Average Time? I was trying to remember someone else who had this problem. He said he just increased the AT till it didn't jump around so much. It didn't take to much adjustment tho'.



I think the AT comes from the factory at . 04 (might be wrong). It still reads every . 01 but only displays the AT that you pick.



HTH

 

[Motorhead]

I got rid of the decimal point when I first put them in. Today I switched sensors with the boost. It now reads smooth. I don't know if SPA carries any warranty but I'm going to get a hold of them on Tuesday. I'll look into that Average time. THANKS!!

 

[BarryG]

Motorhead:

When I moved my spa fuel pressure gauge from prefilter to post filter on the bottom of the fuel filter cannister with a 3' ss braided hose and mounted the sender up by the firewall I ran into a similar problem. It would work fine for a couple weeks then start jumping up to 30 then down to 2 etc etc. If I unhooked the sender from the hose it would clear up again for a couple weeks. I installed a needle valve at the sender. I have it closed except for just enough to get the reading and it has been rock steady since and its been several months now.

 

[Motorhead]

barryg41, I found that feature in the instruction book. It was set at . 4 (seconds?). I re-set it to 2. 0 and it seems to be better.



BarryG, I agree with what you said about fooling with the sender line and then the guage working ok for a few weeks. I made up a "plug" out of 5/16th aluminum round stock and drilled a . 035" hole through it to make a restrictor. It seemed to help for a while but then as you found with your guage, it started to "roam". Try what barryg41 (are you two related?) said to do. This feature is a time delay in the guage as to how often it takes a reading from the sender. I am going to try a smaller restrictor in the line also. I have always noticed that pressure sending units have a very small bore hole.

 

[BarryG]

Motorhead:

I think what we are seeing is the pulsation of the vp44 wreaking havoc on the sender. I no longer have a problem since I put in that needle valve and been about 4 months. I think my avg is set to . 5 second. My needle valve is almost all the way shut. I think you are right if you use a smaller hole for your restriction you should be ok. I would start with the smallest you can make and only make it bigger if it doesn't read on the gauge.



By the way no relation to barryg41 at least that I know of anyway.

 

[barryg41]

The only thing barryg and I have in common is that we lived in the same state for one week. I stayed with some friends a loooong time ago.



Did you guys completely bleed the hoses to your sender? I have bleeders on both pre and post hoses. You can see my install in the readers rig. The Dakato Digitals is limited to hi and lo reading times. NO problem! It works good for me.



It seems to me that if you have any air in the lines that it will cause pulsing on the gauge readout. I know! I know! A lot of guys on TDR has not had this problem. I think that any time you get rid of air you can't compress it. If you get all of the air out and have the right AT. I think it will be a good setup.



Bleed air or not... :-{} that is the question... .

 

[Motorhead]

bg41, the guage actually worked with less roaming around when the line was NOT bled out. I set the "AT" on the guage at 2. 0 and it is smooth now. I AM going to put in a smaller restricter.

Thanks for all input..... BarryG:-{} barryg41... ...

 

[JohnMcIntyre]

Needle valve set-up?

Originally posted by BarryG

Motorhead:

I installed a needle valve at the sender. I have it closed except for just enough to get the reading and it has been rock steady since and its been several months now.

Don't suppose you have any pictures, or part numbers to hand Barry? I experienced this sporadic effect some time ago and generally, I've been happy with my SPA set-up. I basically maxed out the AT time, so that the elapsed time between consecutive samples of instantaneous fuel pressure values would be more steady and it was a big improvement.



Apart from ensuring the electrical connections are all rock solid, it seems that the proximity of the sender to the fuel filter, even in the post filter location, like you have it, go a long way to achieving a steady reading. But, you and the little trick with the needle valve and hose to reduce the sensitivity of fuel pressure surges seems to have nailed this once and for all. Was it a bit of trial and error to get the correct setting for the needle valve and now that you've effectively reduced the sensitivity to "normal", did you change the AT value to something less than MAX or leave that at MAX? Like I said before, pictures and some more words would be very useful Cheers!!

 

[illflem]

TST who sells fuel pressure adaptors for 12 valves recommends air in the lines to smooth out the pulsations. In fact they carry it a step further and recommend also installing a inline fuel filter full of air in the line to the gauge. They also say that it won't be long till all the air is replaced by fuel. Needle valve works for me.

 

[BarryG]

John Mc:

I don't recall the part number but it was just a 1/8npt female to 1/8npt female needle valve that I got from Grainger. I took a look in their their catalog (which is no where near complete to what they have online) their stock number 6MM66 is similar. Except the one I got is 1/8 npt female on both ends instead of 1/4 compresson fittings. If you go to www.grainger.com and do a search on needle valves you will come up with quite a few and just read through until you find the one that fits your setup. If I recall it was less than 5 dollars. Though shipping to you will certainly add to that.



I just did a quick search this may be the one I got



http://www.grainger.com/Grainger/productdetail.jsp?xi=xi&ItemId=1612835366



Hope that helps.



Almost forgot John. I closed the valve all the way and opened it just enough to get a reading. Which by the way is barely open at all. I then used a zip tie to secure the valve handle hoping that vibration etc wont let it slowly open. So far so good. I used a 3 foot section of either 3 or 4 an braided stainless line (summitt racing fuel gauge connector kit) attached to the bottom of the fuel filter canister. I figured that 3 foot of line would take care of vp44 pulses but looking back using braided line probably was not the best thing for that idea since it does not flex - the pulse has no where to go except right on up the line- the ss braided hose can't absorb the pulses like a rubber line might. Anyway since that didn't fly I added the needle valve that I read about a long time ago from a thread that I think Illflem posted. My AT is set to . 5.

 

[JohnMcIntyre]

Thanks for the input guys!

Cheers! this'll give me something to tinker with when I get back to England later this week.



JMc

 

[illflem]

Here's a link to any kind of needle valve configuration you may need

http://www.grainger.com/Grainger/ww...atable=true&adobeCompatable=true&CatPage=3016