When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have a 4303 magnafuel pump and think its on its way out.
On start up and at idle we have right at 40psi. As soon as you give it a small amount of throttle the fuel pressure begins to drop in to the high 30's. The higher rpm the more the pressure continues dropping into the low 30's to high 20's.
I checked voltage at the pump and its between 13.7 to 14v's at idle and when revving the car up, so I don't believe we have a voltage problem. I swapped the pressure sensor for a gauge and the confirmed its not the sensor.
I've checked the fuel filters and the are pretty clean. Reassembled the filters and the problem is the same.
Fuel pressure hasn't been an issue until now, right before I put it away for the winter I ran a tank of 93 through it so the fuel system would not be sitting for months with E85 in the tank. Also pulled all the injectors and had them flowed and cleaned over the winter.
Before I send this pump to magnafuel for them to service it is there anything else I should check over and has anyone else had a similar problem?
Might check the filters as well. FWIW I sent my 4303 in to be checked since i'd ran ot for 3+ years and bought it used. They were super quick and overhauled it cheap. If your filters and voltage are good, send the pump in. They are pretty sensitive to pre pump filtration. I didn't even filter mine pre pump and used a 12An supply off a sump. It was a work horse and them some. Also blasted it with 16v.
Might check the filters as well. FWIW I sent my 4303 in to be checked since i'd ran ot for 3+ years and bought it used. They were super quick and overhauled it cheap. If your filters and voltage are good, send the pump in. They are pretty sensitive to pre pump filtration. I didn't even filter mine pre pump and used a 12An supply off a sump. It was a work horse and them some. Also blasted it with 16v.
Filters were pulled / looked pretty clean and the problem is still there. Glad to hear yours lasted a few years.
I think I will buy another pump, get this one repaired and keep as a spare.
What size and type of pre-filter did you use? Feed line size? Its odd it would crap out. They are basically some rock crusher gears w a high quality electric motor. If you do send it in, they will be able to tell if the inlet side was starving for fuel… or if it was a brush issue. Aside from that, there’s really no reason for them to fail. Might look into a small pump like an aem400 or similar. Then stage the big pump in parallel. MUCH quieter and doesn’t heat up you fuel near as much as a big pump.
I've been running a 4303 for about 5 years. I run a -12 from the tank to pump with no pre filter. The post filter may "look" clean, but that doesn't mean it is. I spray mine out with brakleen and run them under the faucet. That is exactly what magnafuel told me to do. The water on full blast should run out of the filter as fast as it goes in. Simple test to see if it is actually clean. I thought mine was clean too until I tried that under the faucet test.
Feed to the pump is 10an with a 100micron filter then through the 4303 pump to 8an line with 10 micron filter.
I have a new pump and new filters cartridges.
Also going to add an inline ball valve before the filters and pump to make filter changes less of a hassle.
Are you using the magnafuel filters or some other brand? You really need a -12 an feed as that is what Magnafuel recommends. What regulator and where is it located? Return system correct? The magnafuel is good to 900 rwhp on E85, but it's a little picky on how it's setup to get you there.
100mic pre filter is likely too much as well. Just depends how much it flows at 100mic. They will be able to tell when they tear it down if it was starved on the pickup side.
i use one as an aux pump on a hobs, lasts about 2 years usually
the brush kit is like 35bux and the oring kit is about 20 iirc, these pumps are very simple to rebuild. only other thing that needs to be done is to clean up where the brushes make contact to the armature.
That seems odd. Using one as an aux pump, you’d think it should last like 10 years. Do you use a -12 supply unfiltered? Might try it. I ran mine constant duty over 3 years and bought the pump used that already had 2-3 years on it. As an AUX pump, it would never really wear the brushes. What wears out in 2 years time? Genuinely curious, not being a ******! Lol. Thanks for the pics... do you ever take apart the pump housing?
Since discovering 2 AEM400’s flow more than a 4303 (and are cheaper) That’s what I run these days. I’d build 2 aem400’s and use that rig as my “aux pump”. Then run a small quiet pump to cruise around on. Another AEM400 would likely make the most sense. This way you’d have all the same pumps in the system and could carry a spare or two.
problem with using as an aux, im guessing, is it goes from off to full blast as soon as the relay closes. there was still some brush left it just broke away from the lead
10an feed with magnafuel pre filter for a while, then the aeromotive 12an (was going to switch it to a 7gpm). i think they were(are) 75 or 100microns
I'll see if i can find the pictures but the rest of it is just assembled stator on the housing and the armature just free floats and the bearings on each end center it, pain in the *** to get back together. where the brushes make contact was a little ate up so i just flattened that back out, brushes are spring loaded so i didnt worry about removing material from it.
the actual pump gears i took the cover off of just to inspect for any damage to the gears but it all looked clean.
I'd almost have to think there was excessive friction on the gear side causing the motor to work too hard? Restricted feeds will do that as well. They cause odd gear wear patterns according to magnafuel. I had -10 on mine as well. They of course suggested the -12. Though I always run un filtered pre pump. Figured they basically have rock crusher oil pump gears, little dirt wont' hurt them much. I run the large 10 mic spin on agricultural paper media filters post pump.
those gears may look tough but it doesn’t take much abrasion to murder pump efficiency
Makes sense. Can only go off of what i've done personally with that pump. Seemed to make 800-900ish whp on E85 ok for many years without a pre filter. Could have just gotten lucky.
Update, brand new prefilters and post filters along with a new 4303 pump and we are right back to good fuel pressure.
I think my attempts to clean the filters with brake clean and compressed air were a waste and moving forward I will just swap the filters out for new rather than try to clean them.
As for the original 4303 its going to magna fuel for them to check out and I will keep it for a spare or add it for a 2nd pump if needed down the road.
i use one as an aux pump on a hobs, lasts about 2 years usually
the brush kit is like 35bux and the oring kit is about 20 iirc, these pumps are very simple to rebuild. only other thing that needs to be done is to clean up where the brushes make contact to the armature.
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Slideshow: From wobbling harmonic balancers to failed EBCMs, these are the issues that define long-term C5 ownership and what repairs typically involve.
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Slideshow: A modern Camaro transformed into a retro icon, this limited-run "Bandit" build blends nostalgia with brute force in a way few revivals manage.
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Slideshow: Cadillac didn't just crash the high-performance luxury vehicle party, it showed up loud, supercharged, and occasionally a little unhinged...
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Slideshow: A one-off sports car that looks like a vintage Italian exotic-but hides a C6 Corvette underneath-just sold for the price of a new mid-engine Corvette.
4303 Fuel Pump Troubles 
