Info for users of the SPA FP gauge

[Bigsaint]

I originally had my SPA pressure/temp. gauge set up on the Schrader test port, pre-filter. In this location, the SPA was taking pressure measurments at every 0. 1 second, averaged out over a period of 0. 4 seconds. This is the factory setting for the SPA, I believe. The display will always update at a rate of 0. 4 seconds, according to the manual. This was fine for a pre-filter location, the psi's were stable at idle and at WOT.



When I upgraded my fuel lines and moved the SPA sender to a post filter location, directly under the OEM fuel filter housing, a problem arose with the psi's. Not really a problem, persay, more of an annoyance. The psi's were fluctuating (sp) with a +/- of 3 psi's, whether at idle or at WOT. I have my Mallory set at 12 psi's @ idle, but in the new location I would see a constant jump from 12-11-12-13-12-11-12 and WOT runs would read 8-9-7-8-7-6-8, etc.



I found a simple fix by just adjusting the 'At' average time from 0. 4 seconds to 2. 5 seconds, so that my SPA now averages the readings it receives over a time of 2. 5 seconds. Psi's are now again rock solid at 12 psi's @ idle and 8 psi's @ WOT.



Probably most of the SPA users are aware of this feature, but I thought I would throw it out here for anyone who is not and is experiencing the same fluctuations that I had and in need of a cure. My only thought of why it is happening at that location is the proximity of the VP44, less than a foot of fuel line away. My guess is that the VP44 is sucking fuel as the Mallory is pushing, causing a slight turbulence in the line ? If you doubt that the VP44 sucks fuel, when my Mallory went toes up, my SPA was showing -11 psi's at idle. This was at the post filter location.



Scott W.

 

[dresslered]

Are you running your sender remotely, Scott? If you are post filter you are seeing the pulses from the injection pump. These pulses can be extremely tough on the senders and you might be looking at a failure down the line. Mount the sender on the fender with some rubber tubing to act as a snubber and your problems will go away. Changeing the averageing might clear the display, but will not relieve your sender.



P. S. I had a friend loose three SW senders when mounting directly on the injection pump. When he finally mounted the fourth remotely, it has been problem free (no fluctuations either).

 

[Bigsaint]

That's good information David and the pulses from the VP44 are something I didn't consider. Both of my mounts, pre and post filter, were/are not mounted remotely. Something to consider... .



Scott W.

 

[HVAC]

You Da Man!

Thanks for alerting the other SPA users super Scott



For the last year plus I've been studying fuel pressure with my SPA's and I too slowed the AT down. I would add that being able to read negative numbers is a nice feature the digital gauges provide.



Enjoy your SPA gauges!

 

[Rambling]

Sender types?

What were the type of pressure senders that failed? Were they both analog and electronic pressure transducerstypes or just one type?



I had an electronic pressure transducer that failed. It was mounted on the filter's monitor output port.

 

[Bigsaint]

Nowel, no, THANK YOU!!!

The support and advice that I received from both you and Brandon were beyond my expectations. I agree, very strongly, on the negative pressure readings as well. Don't want to beat a dead horse here, but the -11 psi's @ idle was my first clue on the Mallory episode. Guess that an analog gauge would have shown zero, which would obviously be a good clue, but it was sure interesting to see that the VP44 does suck, no pun intended .



Rattlin, that's a good question and I don't have the answer. I can tell you that I have spoken with Brandon in regards to this matter and I believe he has yet to see a SPA sender fail, and he has done a ton of SPA FP installs at his shop, so I'm sure that, if one did fail, the customer would let him know.



Scott W.

 

[Swayse]

SPA Fuel sender

Do you have to ground the fuel sender? I just used a short piece of 3/8 hose to mount my sender on the injection pump(until I get my Ray T Banjo bolts). I worked fine for a little while. Then it started to jump around any where from 40 to -40. I tried to ground it with wire and a couple of hose clamps, still jumps around. Is my sender toast?



To you guys that use a long grease gun line to mount remotely, are you grounding it and how?

 

[Steve St.Laurent]

Here's how I mounted mine:



#ad




My lines are running to a different location than yours would be because I have a '98. 5 with a different style fuel filter head. What I did was cut two slots in an aluminum bracket and ran a hose clamp through the slots and around the sender. It seems that nearly everyone that's had a sender fail has had it mounted direct and not remotely, that engine shakes big time - HARD on electric senders.

 

[dresslered]

I use the grease gun hose to mount my sender remotely. I am using the autometer electric fuel pressure sender which uses a 3-pin conection which already includes a ground. If your sender does not include a ground, you will have to adapt one (maybe solder one directly to the input port???).



The vibrations from the engine are enough by themselves to warrant remote mounting. However, it is the pulses from the injection pump that usually end up killing the senders. The impulse load (known as waterhammer) is devestating to ALL transducers regardless of whether the gauge is digital or analog (this is the same phenomenun as when you flush your toilet that does not have an air column, the pipes will rattle). The pressure transducer sensors utilize a rigid diaphram (which usually only moves on the order of a thousandth of an inch) as the primary sensing element which is literally "pounded" when proper snubbing is not utilized. When a large impulse of fluid hits this diaphram it can be bent beyond its elastic limit. Even if the sender is not completely damaged, the diaphram can become distorted enough to give inacurate readings. Pre-filter mounted senders are isolated from the injection pump but are still prone to the vibrations from the engine. Like I have already stated, I use rubber tubing and purposely left a column of air in the tubing. This effectively dampens the pulses traveling through the noncompressible fluid.



Nowel, I don't know why you would ever want to measure the "sucking power" of the injection pump?

 

[HVAC]

Toilet Analogy???

Dave, maybe you could take a ride with me at the next Ram Runners meeting. I think my truck may have that waterhammer problem. It seems to occur when I floor it and it's accompanied by a loud squeeling sound Should I install a vent stack on the tank

 

[dresslered]

Actually Nowel, I think that it was a very good analogy! Your truck is the only one that I know of that uses sewer pipe for the exhaust.

 

[Rambling]

I believe the type of sender shown in Steve's photo are resistive/mechancial type senders. If anyone has a sender that is about 2. 5 inches long and aobut . 75 inches in diameter, they are most likely the solid state pressure transducer.



I mispoke in my earlier post calling them analog and digital. More correctly the two types are mechanical and solid state senders.



Any info on the type that had problem being mounted directly on the fuel filter would be appreciated.

 

[dresslered]

Both types of senders experience the problems for the previous mentioned reasons. The friend that I referred to had the SW sender. This seems to have the most frequent failure rate, though it is probably also the most commonly used. Stewart-Warner senders also seem to be the most common sender used in small aircraft applications as well, although different scales and gauges are used. I think that they are probably a very good sender.



Mine is the autometer which is what I believe that you refer to as the transducer type. I have also heard of failures of this type. I don't think that there is any substitute for proper mounting methods. Both types of senders, whether they are resistive or capacitively coupled, require a mechanical movement.



Temperature gauges on the other hand which use a solid state thermistor (no mechanical movement) are perfectly safe to mount on the engine.

 

[Swayse]

Good news and Bad news

Good news is that I mounted it remotely and it works perfect now. Bad news is that I have -1 psi at WOT! Here we go again, time to save up for pumps and lines. I don't think the Ray T Banjo bolts are going to do it, but we'll see after I get them and get them in.



Going to the drag strip tomorrow, I'm going for a 14. 9. Last time I went I got a 15. 41 @ 90. I took down the 2. 5" lift in the front and lowered it 1. 25 in the back, and took off the 315/75/16 and put the stock 265/75/16 back on. I even took off my tool box. I took off the stock air box with the paper filter and went to the Psycotty air. Think I can do it?

 

[Bigsaint]

Peter, this is just me talking, but if my FP was -1@ WOT, the last thing I would be doing is racing. It's just not worth the risk of the VP44 IMHO. Curious, what's the psi's @ idle reading?



Scott W.

 

[Swayse]

At idle, I've got 11 psi. If I bump the starter and let the fuel pump run I've got 13 psi. Cruising at 70 with about 7 psi boost, I've got about 7 pounds of fuel pressure. This is my second lift pump, the first one was really bad, 8 psi at idle.



My EGT's are really high too, 1700 degrees pre and 900 post. My stock clutch is slipping a little, I haven't had time to put the new SB clutch in. But, racing is just a blast, I can't help myself. This is the only time I'm really rough on it, the rest of the time I drive pretty good. I've got 53,000 miles on this thing, and I'm planning on keeping it for four more years. I shouldn't go racing, but I just added diesel fuel conditioner, so everything should be alright, right?

 

[Bigsaint]

Thanks Peter. My idle psi's are at 12, post filter. Maybe the banjo bolt upgrade will help you as I can't drag it down below 8 @ WOT with the Aeroquip elbows and no inbound banjo bolts. Certainly won't hurt ya.



Scott W.

 

[Swayse]

Didn't get to go racing, my parents had a wreck about 120 miles into a short vacation. Had to pick them and their car up. Nobody was hurt, just a little shaken. Somebody decided to make a u-turn right in front of them.



I think I may go with a fuel pump and fuel line upgrade, this bombing thing is getting a little$$$$. Pay now or pay way more later.

 

[Bigsaint]

Peter, sorry to hear about the accident, glad no one was injured. Big 10-4 on $$$$. I can tell you that I am REAL HAPPY with the fuel line upgrades. As for the Mallory, so far so good on the second one, keeping my fingers crossed. I really like Steve's idea of having a second pump pushing fuel up to the first, if, for no other reason then having the ability to still limp home if one fails.



Scott W.

 

[Swayse]

Thanks. I may try that Holley Blue pump I have laying around. Put close to the tank and push the fuel to the stock pump. Since I have a fuel pressure guage I can see what's going on.



Cool Dogs by the way.