8 replies to this topic

[dickcdawg]

On 1.6l, have OEM type adjustable fuel pressure regulator set at 46 psi at idle. With rear on jack stands, wheels off, I run the engine up to 5000 rpm in 3rd gear while applying brakes to load engine for a few seconds.  We observe the FP increasing to around 56 psi on same gauge. Is this FP increase normal, if so is it due to tube connected to intake manifold sensing increasing vacuum?

 

Dick Hancock

#39 ITA, SeDiv

[Tom Hampton]

I don't have your type of AFPR, I have the Advanced Autosports 1.6L kit and I do NOT see this magnitude of change.  I see a fluctuation of maybe 2 psi throughout the RPM range, which more wanders around the idle set PSI (not a monotonic increase under load). 

 

PS: 46 psi at idle seems high, and 56 psi is waaay high.  Do you have a wideband O2? 

[OctaneNation]

Dick,

 

The vacuum hose will lower fuel pressure when there is engine vacuum (i.e. anything other than wide open throttle). It helps the computer control idle mixture as the fuel injectors can be open a little bit longer because the fuel pressure is lower. With that said your fuel pressure sounds quite high.

 

On a related note, is the vacuum connection necessary? Modern EFI systems correct the AFR when closed loop (i.e. low speed, part throttle), and apply this same correction at WOT. Is the 1.6L system is primitive enough then this doesn't matter. I have to do something with my 1.6L FPR and was likely going to modify the one I have but would lose the vacuum reference.

 

Cheers,

Matt

[Bench Racer]

Check out the 5X Racing FPR claims. They start with the OEM FPR, they continue using the vacuum lie to maintain constant pressure as was set via their added adjustment feature. Have one and maintains preset pressure. 

[davew]

The vacuum does nothing at wide open throttle, which is all we really care about. It is strictly for low rpm drivability and idle quality. Unless you have a turbo or supercharged car. Then you need a reference for increasing fuel as boost increases.

 

Your stated numbers seem VERY HIGH for a 1.6 car. But since you are ITA you may have optional equipment that a SM is not allowed.

 

dave

[dickcdawg]

Yes, I realize my static FP is high.  My core issue is that I added a header & cold air intake after moving from SM to ITA, and in the first weekend out I had unexplained changes in AFR on my wideband O2 meter.  With the FP set at 38 psi (same setting I ran before the header & cold air intake) I could run several laps and AFR would be in the 12.5:1 area as expected(on straightaway pulls in 4th gear around 6000 rpm).  On the very next lap the guage would peg at 16:1 and stay there, not fluctuating when I lifted or coasted.  Not wanting to risk engine damage I came to paddock immediately to check FP & plug condition.  Plug insulators did look a lot whiter that before the header, but base circle color didn't seem to indicate being way too lean.  So, as a precaution I bumped FP to 46 psi and went out for 2nd qualifying session where I ran all laps with AFR in the mid to high 11's.  Next session was a 90 minute Enduro & AFR stayed in the 11's for 7 laps, then it pegged at 16 again so I had to DNF.  Raised the FP to 50 psi, and was able to complete another quaifiying session and 2 Sprint races, with the AFR in the high 10's to low 11's.  Plug insulators were still white but the base circle was definitely black - matching the rich AFR reading. 

So, back home I started trying to figure out the 2 'pegged at 16 occurrences'.  That's when I ran the 'brake loading' tests and noticed that the FP was NOT CONSTANT as engine load increased.  I chatted with the NGK tech guys about O2 sensor failure modes, and one comment they made was that running too rich could 'fuel wash' the sensor & make it output the 5 volt max that gives a 16:1 AFR reading - when it cools back down it operates normally.  So, I'm wondering if my Adjustable FPR is randomly allowing unregulated 'pump pressure' to occur and cause the fuel wash scenario.  Next step will be to put a good OEM FPR on, run the test, & see if FP still rises with load.  Any other ideas I should consider??  

 

BTW, motor is a crate motor several years old, head has never been off it, but compression is still very good & leak down is <5% on all cylinders.  Timing is at 12 deg BTDC, & ECU is OEM.

[Bench Racer]

A year or two ago my AFR went from 13.5 to 21. Didn't finish race. Plugs looked ok. Found the Innovate Motor Sports 02 wide band sensor required to be recalibrated in free air. Removed the 02 sensor, recalibrated with sensor laying on floor. Found the recalibration was required by reading the potential faults in the instruction booklet. Works great since.

 

Using a cold air intake if cooler air is entering the filter will lean your mixture, hence higher AFR number. May not be your total high number issue.

 

These ^ are two items that could be impacting you AFR number.  

[dickcdawg]

Thanks Bench. Have new O2 sensor for the AFX wideband arriving this weekend - will make sure to calibrate it in air...

 

Dick H.

[Diller]

The need to add FP also could be an indicator that one or more injectors are not opening and closing as they should and you are needing the others to add a lot more fuel to get the total AFR back down. May just be a wonky 02 sensor but something to keep in the back of your mind.