17 replies to this topic

[Andy Mitchell]

End of last season I started to get small but significant fuel pressure variations that I think were the fault of my adjustable fuel pressure regulator. Anybody else ever experienced this? There's not a lot inside of one of these things, so I'm trying to figure out what could be wrong with the thing.

 

The item in question is an Aeromotive, if that makes any difference. It's on a 1.6, and normally is set around 38 PSI. After quite a long time of just faithfully doing it's job, it has started to meander around thru the race day. Always goes higher than desired (to a max about 48 or so), but it isn't consistent - FP goes up then comes back to normal like it's got a mind of it's own. Any thoughts? Should I rebuild or just chuck the regulator and buy a new one?

 

Thanks in advance for an help that is offered.

[MPR22]

End of last season I started to get small but significant fuel pressure variations that I think were the fault of my adjustable fuel pressure regulator. Anybody else ever experienced this? There's not a lot inside of one of these things, so I'm trying to figure out what could be wrong with the thing.
 
The item in question is an Aeromotive, if that makes any difference. It's on a 1.6, and normally is set around 38 PSI. After quite a long time of just faithfully doing it's job, it has started to meander around thru the race day. Always goes higher than desired (to a max about 48 or so), but it isn't consistent - FP goes up then comes back to normal like it's got a mind of it's own. Any thoughts? Should I rebuild or just chuck the regulator and buy a new one?
 
Thanks in advance for an help that is offered.

It is more likely your fuel pump is the culprit. If it isn't running optimally you might think you are having regulator problems because the FP will drift up and down quite a bit. Had a pump going out last weekend, once we changed the pump out we gained 6 lbs of fuel pressure. Pull pump, check sock filter, if clogged, change and reinstall see if pressure goes up. If not, change fuel pump, if it doesn't go up then you may have regulator problem.

[Andy Mitchell]

Cool! Thank you very much, I've got a spare pump that I'll swap over to. I would never have imagined that the FP could go high with a failing pump.

 

But then again, I couldn't see how anything short of a bad diaphragm would mess up the operation of the regulator, so it's at least as logical as anything else I've considered.

[FTodaro]

I can be the pump, it can be the gauge, it can be the regulator. 

when you turn the car off how long does it take for the pump to bleed off the pressure? if it bleeds quickly like a Minuit or two that could be pump issue. I would start with a different gauge or check it with another gauge to see if the reading is correct. easier than pulling and replacing the pump as the first step.

then if the gauge is accurate I would go to the pump since you have one. then if it still persist go with the regulator.

 

I have had issues with all three at some point. I now run an electric fuel pressure gauge in the cockpit and keep an eye on it.

[Andy Mitchell]

Thanks for your interest! the System holds pressure fine, don't know exactly how long to bleed down but at least 10 minutes or so. Probably longer actually, I never really checked. Lots of time to get out of the car, pop the hood and look at the gauge, anyway.  

 

I don't think its an incorrect reading on the FP gauge, as the mixture really seems to be going rich. I saw readings down into the high 10's on the A/F gauge during a 1-hour enduro we ran near the end of the season, and it did it again in a 3-hour race a week later. We started right on the button in both of those races (A/F 12.8 or so at the end of our back straight, which is the only place I really have time to check).

 

That one hour race ended with the mixture rich, but for some reason I didn't bother to look under the hood right away (it was last points event of the season, and it was a hot day - I guess I was thinking more of having a beer than fixing the car at that point). Anyway, the regulator was back to 38 on the next cold start, so it was sort of a mystery what was going on. However, in the 3-hour race the next weekend things started out fine, then it all to hell for a bit and then came back to almost normal by the end. Regulator was reading 46-48 at the end of that. Plugs were black afterwards, which is not normal with this car when it's running well.    

[davew]

Probably not the pump. Pumps do not fail with more pressure. If you replace, use only a new (expensive) Mazda pump. They are the best.

 

Sounds like debris in the regulator to me.

 

Dave

[MPR22]

Probably not the pump. Pumps do not fail with more pressure. If you replace, use only a new (expensive) Mazda pump. They are the best.

 

Sounds like debris in the regulator to me.

 

Dave

Pump has a clog, you set FP with regulator, clog goes away intermitently, fuel pressure goes up.  

[Ron Alan]

Pump has a clog, you set FP with regulator, clog goes away intermitently, fuel pressure goes up.  

I dont think that is how the FP regulator works. Pump would have to be putting out the exact pressure you wanted to start with and the regulator be set above that pressure...then the pressure could actually go up if the pump began to create more pressure. Regulator will not allow more pressure than it is set for regardless of how much above that pressure the pump is making....assuming it is working correctly

 

Recently found out the hard way that the fuel pump pressure can change with the amount of voltage it is running on!! (warning to all)...make sure your alternator is working! Car will run on less than 12 volts but shit happens!

[MPR22]

I dont think that is how the FP regulator works. Pump would have to be putting out the exact pressure you wanted to start with and the regulator be set above that pressure...then the pressure could actually go up if the pump began to create more pressure. Regulator will not allow more pressure than it is set for regardless of how much above that pressure the pump is making....assuming it is working correctly

 

Recently found out the hard way that the fuel pump pressure can change with the amount of voltage it is running on!! (warning to all)...make sure your alternator is working! Car will run on less than 12 volts but shit happens!

Pressure or vacuum is not just a matter of set it an forget it.  It is directly related to the VOLUME of air, liquid..... that is being flowed through an orifice.  In my scenario the pump is clogged, the orifice is reduced.  Then we set the fuel pressure, when I changed out my pump what we thought would be 51 psi now became 58 because of the increased flow.  Real world example of what happened to me last weekend.  And on these damn cars, when in doubt about the fuel delivery problem change the fuel pump.  10 minutes of work.  

 

My father, the brilliant engineer, who holds patents for some of his designs could actually explain some of this stuff much better than me.  I just do trial and error and look for results.  I do have a good memory so I can remember the cause and effect relationships i have witnessed through experimentation.  

 

Your favorite Savage

[Ron Alan]

I think we said the same thing?  And I'm not an engineer...so being corrected is constant learning! And god knows I'm always learning (and forgetting ) 

[Duane Polsley]

I think I've seen similar problem with a restricted return line.

[Andy Mitchell]

Thank you all for your comments.

 

Pump, return line, regulator - those are all plausible sources of the problem, so I guess it's time to pull everything apart for a good cleaning/inspection. I was secretly hoping that a whole bunch of people would jump in and say they'd experienced similar problems caused by bad regulators alone, but no such luck.

 

Just a question: can you still get OEM Mazda fuel pumps? The spare that I carry is one of those cheapo Chinese jobs, the kind Dave warns against. I bought it because I never thought I'd have to use it except in an emergency, and it was about 1/4 the list price of the Mazda one. We get a discount on OEM Mazda parts through a local dealer that sponsors our series though (and I've got some contingency money built up with them anyway), so I'd have no problem going and buying a 'good' one if it actually was going to be better.

[Dave D.]

Fuel pumps from Mazdaspeed(with our discount) are still expensive relative to what they really are at $200 (just a pump,not an all inclusive tank "module") and I can get a Denso unit  for around $80  Jobber price(I own a repair shop). I wonder if Denso makes the pumps for Mazda?

[Steve Scheifler]

And what's wrong with the Bosch units for about $80?

[Dave D.]

And what's wrong with the Bosch units for about $80?

Nothing as far as I'm concerned, I can get either for the same price basically. I was just wondereing who the OEM supplier is??

[davew]

Take it as friendly advise given for free. Which is always suspect.

 

If you check with the most experienced people, shop owners, who deal with these cars on a daily basis. You will find that we use new, Mazda units only. They are expensive to buy. But in the long run are better.

 

dave

[Steve Scheifler]

Dave, who makes them? Whatever it is, it almost certainly is not exclusive to Mazda. I appreciate your experience and advice, but there are tens of millions of cars running the major name brand pumps for 100x more miles than any SM will ever see, without problems. It is a very standard piece that is used in countless different makes & models with nothing more than the wiring connectors and/or screen connection to tell them apart. So if there is something special about the severely over priced mazda unit, I would very much like to know what.

[ChrisA]

The OE unit on a NB and I think most NAs is the China made Mitsubishi UC-T30. It was used in the stellar 1.3L Suzuki Sidekick. It was also was used in some sport bikes. I do not think it is a "better" unit than a Bosch/Denso, but it does fit better. Bosch & Denso may now be the same unit rebadged. Specs for any of these units are difficult to find. On the NB, the Bosch/Denso does not mate with the OE pump hanger cleat well at all. The Walbro 190 Standard does come with an isolator that mates with the cleat. However, the Walbro utilizes a gerotor design, which may not perform as well in the low gas/no gas (sloshing) that we can see towards the end of a race. The impeller design of the OE/Bosch/Denso should work better in that regard. It is also a more current hungry design.