Topic: A/F Ratio

[chrisfranklin]

Just checking opinions here. If you suspect the A/F ratio may be off on your slightly modified, fuel injected 2.5L, and you are able to accurately establish the present A/F ratio of the engine at all RPMs (and do find a lean condition along the way), which, if any,  of the following would you buy to correct the A/F ratio problem: 

-Adjustable Fuel Pressure Regulator  http://www.quadratec.com/products/17009_102.htm  (Says for 4.0L but then mentions 62mm TB some like me here use)
-Adjustable MAP Sensor    http://www.quadratec.com/products/17010_600.htm
-Ajustable Crank Position Sensor (not sure if this still sold)

The Adjustable CPS solely affects timing but I thought I'd just throw it in there.

[sharpxmen]

Just checking opinions here. If you suspect the A/F ratio may be off on your slightly modified, fuel injected 2.5L, and you are able to accurately establish the present A/F ratio of the engine at all RPMs (and do find a lean condition along the way), which, if any,  of the following would you buy to correct the A/F ratio problem:  

-Adjustable Fuel Pressure Regulator  http://www.quadratec.com/products/17009_102.htm  (Says for 4.0L but then mentions 62mm TB some like me here use)
-Adjustable MAP Sensor    http://www.quadratec.com/products/17010_600.htm
-Ajustable Crank Position Sensor (not sure if this still sold)

The Adjustable CPS solely affects timing but I thought I'd just throw it in there.

Adjustable AFR will give you extra amount of fuel in open loop - a good and simple way to adjust the AFR and also fine tune it as opposed to [only] a set of injectors where you are set on their specific flow

Adjustable MAP - it's not really adjustable, it will only offset the output, so what it does is to output the 1 bar value sooner (so will tell the PCM that the pressure is 0psi or 1 bar absolute at a lower value than really is) and offset all the output along the way - will help some but anything above that will still be interpreted at the same value. But keep in mind that all this is valid for open loop, closed loop will work the same targetting 14.7 afr. compare this "adjustable" map at $135 with the Split Second PSC1 unit at $285 and i'd say the latter is a better deal and is programmable. the "adjustable" MAP at $135 has $15 worth of parts in it  and can be assembled at home very easy so there's really no point in ditching that much cash on it.

EDIT: what it does is to feed the MAP sensor at a higher voltage than 5v stock by using an adjustable voltage regulator to replace the 5v feed coming from the PCM to the MAP, the output of the MAP sensor will then be offset by the extra voltage at which the MAP sensor is powered - so if your 5v line is at 5.2 and your 1bar output was at 5 then the result will be 5.2v at 1 bar absolute pressure - same goes for all the intermediate values proportional to the voltage (80% for 0.8 bar absolute pressure for example - 4v vs 4.16v). I can't remember exactly what was the stock map output at 1 bar abs pressure, i used 5v as an example.

dunno anything about adjustable CPS, but you really don't need to buy one, you can make yours easily (you need to move the CPS position on the bellhousing.

[Sine Deviance]

I would think your best bet is to go with an adjustable FPR. Our fuel pumps are capable of pushing more pressure/volume than the fuel system is tuned for from the factory. Pop on an adjustable FPR and crank up the pressure a little. A bigger fuel rail and bigger injectors will help. If you can bump the pressure in the fuel rail from 39p psi (stock) up to 43.5 psi then the factory injectors should flow a little more (but I don't know how much.) If they become a bottleneck, FoMoCo 19# injectors would be a good, cheap, easy upgrade. As long as you can push 43.5 psi at the rail, the FoMoCo injectors will move 18.25 lb/hr of fuel, whereas the factory injectors move 17.4 lb/hr  (at)  39psi.

Also, you should be able to find cheaper adjustable FPR's than the one they sell at Quadratec. I think that one at Quadratec is so expensive because it comes pre-set for the 4.0L w/ 62mm TB, meaning no further tuning would be required. Keep in mind that the 4.0L fuel rail pressures would be different than 2.5L fuel rail pressures even if you were using the 62mm TB on both engines, meaning that particular FPR will be adjusted incorrectly for your setup out of the box.

[chrisfranklin]

Thanks Sine Deviance, Sharpxmen.   I've got a set of 19lb FoMoCo injectors and a 62mm TB and spacer on there now.  Intake setup I've cobbled together probably flows a bit better than stock.  Man, the 2.5 is one engine I wish was MAF, and something you could chip.   

[Sine Deviance]

I forgot to mention that you should consider investing in a wideband O2 sensor and controller. These will allow you to get a dead-on accurate numerical A/FR reading. These setups are expensive but worth it for serious tuning. You can also use the factory narrowband O2 sensor with an Air/Fuel Ratio gauge. This is usually the cheaper option but the readings won't be nearly as accurate and there will be some guesswork involved. Most Air/Fuel Ratio gauges don't even have numbered faces; they use gradients (Lean<>Stoic<>Rich) instead.

I also found you a cheaper adjustable FPR:

http://strokedjeep.com/regulator.html

There is a core charge, but if you send in your old FPR it'll end up being much cheaper. Should work great. Keep in mind you'll need a fuel pressure gauge to tune any adjustable FPR accurately.

Thanks Sine Deviance, Sharpxmen.   I've got a set of 19lb FoMoCo injectors and a 62mm TB and spacer on there now.  Intake setup I've cobbled together probably flows a bit better than stock.  Man, the 2.5 is one engine I wish was MAF, and something you could chip.   

At stock fuel rail pressure (39psi) the FoMoCo 19# injectors actually flow LESS fuel than the factory injectors. You should swap your factory injectors back in until you can get your FPR and richen up the mix a little.

[sharpxmen]

Also, you should be able to find cheaper adjustable FPR's than the one they sell at Quadratec. I think that one at Quadratec is so expensive because it comes pre-set for the 4.0L w/ 62mm TB, meaning no further tuning would be required. Keep in mind that the 4.0L fuel rail pressures would be different than 2.5L fuel rail pressures even if you were using the 62mm TB on both engines, meaning that particular FPR will be adjusted incorrectly for your setup out of the box.

the 91-95 2.5 and 4.0 have the same fuel pressure in the rail and use the same FPR

I forgot to mention that you should consider a wideband O2 sensor and controller. That will allow you to get a dead-on accurate A/FR reading. You can also use a stock narrowband O2 sensor with an Air/Fuel Ratio gauge. This is usually the cheaper option but the readings won't be nearly as accurate and there will be some guesswork involved. Most Air/Fuel Ratio gauges don't even have numbered faces; they use gradients (Lean<>Stoic<>Rich) instead.

I also found you a cheaper adjustable FPR:

http://strokedjeep.com/regulator.html

There is a core charge, but if you send in your old FPR it'll end up being much cheaper. Should work great. Keep in mind you'll need a fuel pressure gauge to tune any adjustable FPR accurately.

At stock fuel rail pressure (39psi) the FoMoCo 19# injectors actually flow LESS fuel than the factory injectors. You should swap your factory injectors back in until you can get your FPR and richen up the mix a little.

i can make them for cheaper than that - i might have a couple made over the weekend - I sent one to Jeffy for a review. there's a thread with a couple of pics in it. If you guys are interested let me know - same as these they are modded stock ones - the difference compared to the stock is that you increase the pressure applied on the spring (the preloading point of the internal spring) and you can go either way (higher or lower pressure) so potentially you could also run larger injectors and lower the pressure below 39 to compensate

[TrailsLessTaken]

I would be interested in one also

the 91-95 2.5 and 4.0 have the same fuel pressure in the rail and use the same FPR

i can make them for cheaper than that - i might have a couple made over the weekend - I sent one to Jeffy for a review. there's a thread with a couple of pics in it. If you guys are interested let me know - same as these they are modded stock ones - the difference compared to the stock is that you increase the pressure applied on the spring (the preloading point of the internal spring) and you can go either way (higher or lower pressure) so potentially you could also run larger injectors and lower the pressure below 39 to compensate

[sharpxmen]

I would be interested in one also

follow this thread, i will post here once i have couple made http://4bangerjp.com/forums/index.php/topic,8066.msg64641.html#msg64641

[Sine Deviance]

If you want to get a gauge for your new FPR, try checking here:

http://prosportgauges.com/

Great gauges for not much money.

[chrisfranklin]

So, I'd buy an adjustable FPR and also buy one of those Wideband A/F gauges that fits in the O2 sensor area. 

I know the gauge is kind of pricey but I wouldn't be surprised if I need the thing a few times beyond just setting up the adjustable FPR.   

So how do I test the adjustable FPR out?  Do I just screw the Wideband AF gauge in and get a digital readout of the AF at idle, then have somebody hit the gas and go full throttle in neutral and see what the gauge says?  Then bump/back off the adjustable FPR?

[sharpxmen]

So, I'd buy an adjustable FPR and also buy one of those Wideband A/F gauges that fits in the O2 sensor area. 

I know the gauge is kind of pricey but I wouldn't be surprised if I need the thing a few times beyond just setting up the adjustable FPR.   

So how do I test the adjustable FPR out?  Do I just screw the Wideband AF gauge in and get a digital readout of the AF at idle, then have somebody hit the gas and go full throttle in neutral and see what the gauge says?  Then bump/back off the adjustable FPR?

you find a long uphill and floor it - monitor the output of the wideband to tune it. My personal opinion you should skip on the wideband, they go for about $200. If you really want one i suggest also getting a system that logs the output so you don't have to keep your eyes on the gauge while driving (or have someone else drive it while you monitor it). 43 psi should be a good place to start.

at idle won't make much of a difference, your PCM will always target 14.7 AFR in closed loop based on O2 feedback, no matter how much pressure you throw in the fuel rail - what you want and where you can make a difference is open loop

[Sine Deviance]

So, I'd buy an adjustable FPR and also buy one of those Wideband A/F gauges that fits in the O2 sensor area.

Uh... no You buy the adjustable FPR and then you buy a Fuel Pressure gauge. The gauge costs around $40 if you get one of the Performance series gauges from ProSport. You only need to buy the $200 wideband O2 kit if you want to get your exact air/fuel ratio figures. Which you won't need just yet. It's just nice to have at this stage if you've got the cash to throw at it.

I know the gauge is kind of pricey but I wouldn't be surprised if I need the thing a few times beyond just setting up the adjustable FPR.

You won't need a wideband unless your setup is WAY out of whack and won't run, or you have every possible engine mod in the book and want to get it very fine-tuned, or you want to run forced induction (Turbo, Supercharger. Those need more exact figures.) As long as you keep fuel pressure close to the stock values you won't have any problems. 39 psi is stock... I wouldn't go under 39 psi unless you are running bigger injectors that are rated for a lower value. I wouldn't go over 43.5 psi because you're using the 19# injectors and that's what they're rated for. Then give it a run on the ol' butt dyno. If 43.5 psi seems a bit rich, dial it down to 41 psi and give it another run on the butt dyno. It'll probably be damn close. Repeat until it feels good. It won't be exactly perfect but you can get it damn close, and since you're not running forced induction, damn close is good enough. I'll go into more detail below.

So how do I test the adjustable FPR out?  Do I just screw the Wideband AF gauge in and get a digital readout of the AF at idle, then have somebody hit the gas and go full throttle in neutral and see what the gauge says?  Then bump/back off the adjustable FPR?

Nope, nope, nope. Wideband has nothing to do with this, as I said above. You need a Fuel Pressure gauge. Install the adjustable FPR (but don't plug in the vac line yet) and wire up the gauge, dial the FPR where you think it should be (or skip this step if it's pre-dialed) and crank up the Jeep. If the Jeep won't run, that's okay, just leave the key on. Either way, the fuel pump will kick in, and at this point you should get a reading on your Fuel Pressure gauge if you set it up right. For the initial run, ~41 psi would be a good starting point.

If the pressure is about where you want it, turn off the Jeep, tighten up the lock nut on the pressure adjustment screw, and hook the vac line back up. Then crank the Jeep back up. The Fuel Pressure gauge will now read 6 to 8 less psi at idle. This happened when you hooked up the FPR vac line; it put the system back into closed loop unless at WOT (a.k.a. open loop.) This is normal, and the fuel pressure should rise and peak at your original set point as RPM's/throttle increase.

Now, test drive and see how it feels. Be very careful here and heed my instructions. If it feels good, tweak it a little, but you're basically all set. If you get pinging with heavy throttle it means you set the regulator too low and you're running too lean -- if you do get pinging, PULL OVER IMMEDIATELY and dial the regulator up a little. Otherwise, detonation can possibly damage your engine. If you get very noticeable instant loss of power and/or sputtering under WOT it means you set the regulator too high and it's running too rich. Don't worry too much if it's running rich; it won't damage anything, but it will waste fuel and rob you of performance. If the Jeep doesn't run at all, you either threw the adjustment way out of whack or you didn't install the new regulator correctly -- try again

I am guessing that your sweet spot should be between 41-43.5 psi since you're running the FoMoCo injectors. The adjustable FPR, ProSport Fuel Pressure gauge, and a gauge mounting pod should all you need. The gauge comes with the sensor you need and ProSport offers mounting hardware and dash mounting cups for around $10. After all is said and done, I see you spending at least $180 and not more than $250. Final price is dependent on which adjustable FPR you go with and could end up even lower if you get one from sharpxmen.

[chrisfranklin]

I'll probably end up doing like you say.

With the oem FPR, I barely passed CARB emissions tests the last couple of times in the last four years.  So, I'll probably keep that oem one around in case the tests go badly following an adjustment of the new adjustable FPR. 

Of course, setting the adjustable FPR correctly should enable a correct AF flow and enable (theoretically) better emissions values than the present results (still passing, though)

Of course, if I use the gauge to get the pressure setting on for the oem FPR -- like you said, 39psi -- then I just dial that in for the adjustable version for the CARB tests and I should get the same CARB results as now. 

Of course, knowing my luck with CARB, something else will go haywire with the new adjustable FPR (set at stock fuel pressure) in the loop and I'll spend weeks replacing s#$t and running a half dozen emissions tests until I finally get it sorted out for another couple of years.       Gotta love California

[Jeffy]

If you're not passing SMOG II stock then you should really fix what's wrong rather then slapping on a bunch of other stuff that may or may not fix the problem.

[chrisfranklin]

If you're not passing SMOG II stock then you should really fix what's wrong rather then slapping on a bunch of other stuff that may or may not fix the problem.

  I agree Jeffy.  My previous was confusing, but I'm talking about CARB problems after the install of the adjustable FPR.