Fuel starve in left or right corners?

[Croc]

Fuel pumps have this annoying habit of slowly failing so it is very plausible that this is what yours is inflicting upon you.  I would test again and if you think you are getting starvation then replace the pump.  

 

In the meantime just order a new pump from Rimmer Bros and have it on the shelf ready to go.  The pump comes from POS Rover shitbox.  Cross referencing that code on the top of the pump usually cross links to a pump on Rimming Bros.  

 

That comes out via pushing in the little tabs to pull the line out.  Best achieved when you use all 8 of your tentacles at the same time!  Annoying thing.  

[KnifeySpoony]

I've read mixed instructions on the internets - some say simultaneously push in the 3 little tabs. Other people say to push in the ring. I tried the later but was unsuccessful.

[Croc]

2 hours ago, KnifeySpoony said:

I've read mixed instructions on the internets - some say simultaneously push in the 3 little tabs. Other people say to push in the ring. I tried the later but was unsuccessful.

 

Yes I observed the diversity of recommended approach.  However, what eventually worked for me was to channel my inner octopus and use all my tentacles simultaneously to depress the three tabs while cursing the engineer who designed this piece of shit with many bad words not repeatable to nice gentlemen like yourself. 

 

Your approach may differ.  

[KnifeySpoony]

Switched back to hard compound ZZR and still getting apparent starve, but not quite as quickly. Still nothing like the car was behaving previously. Trying to figure out the best way to diagnose before I just throw a new fuel pump in hoping that's the issue (or is that the best strategy?). I could tap the fuel rail for an electronic fuel pressure meter, then monitor for dropouts. Anything that can be done via easymap to confirm that fuel supply is actually the issue?

[MV8]

If you have a ford fuel pump driver module near the tank, then it is an electronic returnless system and has an electrical fuel rail pressure sensor. If you do not, then the system is a mechanical returnless system with a fuel pressure regulator inside the tank next the pump.

 

A mech sys remote  regulator is not as responsive as one mounted to the rail at the injectors. A returnless sys is not as responsive as a return sys off the fuel rail but an electronic returnless should alter injector pulse width based on the pressure sensed by the electronic rail pressure sensor and how long it stays low. A pic of your pump assy outside of the tank would help to confirm regulator placement.

 

I suggest adding a mech regulator near the rail on the firewall with a 1/8npt port for a gauge or electric pressure sensor you can monitor while driving. You can adjust the reg so it has no affect and serves only to provide a pressure indication. If you want to add a return and eliminate the in-tank reg, your half way there already. The original type pump assy can be reused with the mech reg removed and a bulkhead fitting added to the top of the tank to dump return fuel on to the pump inlet but it would be better to swap if there is a return bucket pump assy that will fit the opening. The return should have a tube extending inside the tank to near the bottom to reduce splash/aeration of the fuel.

 

 

Edited Monday at 11:43 AM by MV8

[MV8]

Ok, it is a mechanical regulator returnless system. It is a basic 90s fuel pump system with a bucket to help with slosh. The shiny piece in the middle is the regulator with a ground wire to prevent static build up from the fuel pumping through. It is not as good at maintaining pressure as a return system with a regulator on the rail, but your issue seems to be slosh. The flow out of the regulator could be better directed down into the bucket with a .050" sheet metal baffle at a 45 degree angle in front of the reg outlet, clamped on to the regulator with a heater hose worm gear clamp. Simple to make the baffle with snips and pliers.

 

The float arm that provides the level indication is the only thing that could come loose in the tank and would have no effect on pressure loss during cornering. The bucket is spring loaded against the bottom of the tank when the retaining ring is installed.

 

The three tab snap hose connection is typical of euro fords.

Edited Monday at 02:27 PM by MV8

[KnifeySpoony]

I fixed the float, which fell off into the tank. I have that external fuel pump module thing on outside of the tank. I'm just not sure why I this issue arose. I never had fuel starve before. What is likely to be failing?

[MV8]

I'd add a pressure gauge to the port on the fuel rail then run the engine to check for variation between 35 and 70 psi.

 

Edited Monday at 06:59 PM by MV8

[KnifeySpoony]

I don't have a port on the rail - will a port/bung need to be welded on? Also what do you recommend for a simple datalogger?

[MV8]

I thought this sounded familiar. Not using sensors and the CAT ecu is running a fixed pulse width through the pump drive module to drive the pump at a fixed output with no feedback and the regulator is a safety set to 90 psi it will never see with the CAT setup. It appears to be a 2000-2002 domestic ford focus pump assy. See catmando's post here on page two:

 

Edited Monday at 10:33 PM by MV8

[MV8]

So, as the pump wears, output is less and less like any pump. With this setup, the wear results in less and less psi because the pump drive output is fixed by the CAT ecu. If there were a regulator and a pump running full voltage/output, it would maintain psi until the pump was no longer capable AND the regulator was not bypassing at all at high rpm and WOT.

 

You can't just add the FRP to the rail or fit an oem rail becuase you are not using a ford ecu.

 

Also, as-is, you don't get the benefit of return flow to dump in the bucket when cornering.

 

A bandaid would be to bypass the pump drive module for a full 12vdc to the pump, then swap the internal regulator spring for a lower pressure (whatever a new pump puts out key on-engine off for the CAT tune; 45-55psi?) with no return and performance should return to original. You could also just replace the pump assy but the life will be shorter than modifying the original as described above. Another alternative is to replace the pump assy with a return line type so no drilling to fit a return to the tank. The 2001-04 Ford Escape/Mazda Tribute looks like the best bet but would require a new electrical connector and the gauge ohms may not match up with a focus.

 

What do you want to do?

 

 

Edited Monday at 10:44 PM by MV8

[KnifeySpoony]

I mean, I hate adding complexity, and I'm extraordinarily lazy/dislike "projects" or "upgrades", unlike most of my car-modding/racing peers. So my inclination is to just drop in another pump, if that's likely to solve the issue. It just seems odd that the pump would already be failing in a 4 year old car with 5k miles on it, when they go for 150k miles in a focus/etc...

[MV8]

The pump isn't worn out. It is running at less than full capacity (i.e. running part-throttle in the CAT). In a focus, the ecu would sense the pressure loss, then tell the pump drive module to increase pump output.

 

The CAT also can't compensate for any change in restriction such as a partially clogged fuel filter so you might change that as well.

So many ways to address this but I understand the concern about fuel system changes.

 

A replacement focus pump (from CAT or anywhere else) is not an exact copy because the required output tolerance is wide due to the ability to "throttle" the pump output. For example, you could replace an engine that made 200hp with one that produced 190 at the same rpm because you can throttle the engine to produce the speed you want to go. The CAT has a fixed throttle for the fuel pump.

 

Try a $50 focus pump and see if your problems change.

 

 

[Croc]

19 hours ago, MV8 said:

..... It is not as good at maintaining pressure as a return system with a regulator on the rail, but your issue seems to be slosh. 

 

 

I'm not sure it is just slosh in this instance?  While the Cat tank is a long wide thing susceptible to slosh, you can confirm this by just filling the tank and trying it out on track.  I think the OP has done this and still gets the symptoms.  So not slosh in this case.

 

 

11 hours ago, MV8 said:

So, as the pump wears, output is less and less like any pump. With this setup, the wear results in less and less psi because the pump drive output is fixed by the CAT ecu. 

 

Exactly what I tried to say and failed earlier - very well said.

 

 

 

11 hours ago, MV8 said:

If there were a regulator and a pump running full voltage/output, it would maintain psi until the pump was no longer capable AND the regulator was not bypassing at all at high rpm and WOT.

 

This would be my preferred set up if I was redesigning the Cat system for production plus adding a return line.  

 

Keep in mind, any modification away from stock Caterham fuel system quickly strays into needing to modify ECU map and that gets very expensive in a hurry as you need a password to change it (not readily available).  If you want to change the map then the agents for MBE make you buy a new unlocked ECU, new map and then their tuning time.  As a result the cheapest and only practical solution is usually to drop in a new pump.  

 

 

8 hours ago, KnifeySpoony said:

It just seems odd that the pump would already be failing in a 4 year old car with 5k miles on it, when they go for 150k miles in a focus/etc...

 

Yes but Caterham is not using the pump as Ford designed it to be used which is what MV8 has been saying.  You are also doing track work which loads a lot of physical forces on the pump.as it now sits in its very own gasoline wave pool.  I'm replacing my similar fuel pump every 5 years on average.

 

 

On 10/19/2025 at 4:25 PM, KnifeySpoony said:

Anything that can be done via easymap to confirm that fuel supply is actually the issue?

 

Easimap is quite good for diagnostics but its not going to give you a fault code and say replace this.  

 

You need to buy the not cheap proprietary cable from SBD Motorsports.  Software is free download.  Then go out and log a session on track with Easimap running on a laptop.  Yes I saw it done last weekend by another USA7s member.  Laptop strapped down in passenger seat and recording away while a 420R owner did 25 mins on track.  The data quickly gave the pointer to the problem so the owner could work around it to keep him on track (likely failed lambda in this case).  

 

 

 

So you have two options:

 

1) Modify things like MV8 is suggesting which takes you down a road of making things better than Caterham designed it but may be more complicated and expensive than you want or are technically proficient in.

 

or

 

2) Drop in a new fuel pump and see if it fixes the problem.  If not then save the extra pump as a spare.  

 

 

 

 

 

[KnifeySpoony]

6 hours ago, Croc said:

 

I'm not sure it is just slosh in this instance?  While the Cat tank is a long wide thing susceptible to slosh, you can confirm this by just filling the tank and trying it out on track.  I think the OP has done this and still gets the symptoms.  So not slosh in this case.

So you have two options:

 

1) Modify things like MV8 is suggesting which takes you down a road of making things better than Caterham designed it but may be more complicated and expensive than you want or are technically proficient in.

 

or

 

2) Drop in a new fuel pump and see if it fixes the problem.  If not then save the extra pump as a spare.  

 

 

 

 

 

Slosh is definitely a factor. The starve doesn't happen until after a certain amount of time on track; quicker on stickier tires, slower to happen on less sticky tires. 

 

I think I will just drop in a new pump and see what happens. Simple job and no complexity added. The only challenge is that stupid little connector. Oh and tariffs.

 

Thanks all for your guidance. If the pump doesn't fix it, I'll be back, probably ready to redesign the whole fuel system. Shudder...