Dino's latest project (MAP adjuster)

Since my engine's still running rich with the Ford 24lb injectors, I decided to add some adjustability for my air/fuel mixtures in the form of a MAP sensor voltage adjuster. Here's my article:

http://www.angelfire.com/my/fan/MAP_adjuster.html

This is how it looks now that it's finished:



Stock MAP input voltage is 5.0v. I have mine set at 4.6v and I'll keep adjusting it downwards until I've got the A/F mixture near stoichiometric. Hopefully my gas mileage (18-20mpg) will improve.

Dyno Have you thought about doing an adjustable fuel pressure regulator to help lean out your A/F ratio. I think I have a a how to make your own I got the info off of strokers awhile ago. Thats how I mainly tune my Big block chevy tow rig that taking all my time lately.

It had crossed my mind but I thought that making a MAP adjuster would be easier. The stock regulator is set at only 39psi and I didn't want to set it much lower than that in case it caused problems with fuel atomization.

That is a good point I woner how much of an affect it would have. BUt on another thought I thought the fords ran lower preassure anyways since the 19 lb ford stang injectors normaly put out anout 20.5 or so in a 89 xj(I can't remember what preasure it runs right now. I can't wait to play with my XJs again so I can test some of my newer stuff but my tow rig is taking all my time rightnow.

The '87-'95 4.0 XJ's run a fuel pressure of 39psi like the Fords, so the 19lb Ford injectors also flow 19lb/hr in the XJ.

Dino,

I have followed the MAP thread here & at Strokers. The MAP turn-down route should help with your open-loop ECU (compared to with an O2 sensor in closed loop, where it only impacts acceleration enrichment).

Have you thought about placing a fuel regulator inline with the factory 39psi unit, one that regulates at a higher pressure? The regulator is on the return line, and a higher pressure regulator fitted downstream will keep the factory regulator full open (to bleed off pressure) when the secondary is adjusted above the 39psi.

The higher fuel rail pressure will allow tuning of increased fuel delivery from lower #/hr injectors (like your factory injectors, or other 21 & 23 #/hr injectors). The increase in flow is not linear although increasing the rail pressure from 39psi, in an adjustable value to the pump rating of 49psi, will alter the fuel delivery.

If the secondary regulator is ported for a vacuum reference it will also allow for slight throttle position sensitive adjustment of the pressure (just like the factory regulator with the full 39psi only at 0 vacuum and WOT).

No I didn't think of that idea Ed but it sounds like a good one though. For me it was a toss up between reinstalling my stock injectors and raising the MAP voltage to more than 5.0v, or keeping the 24lb injectors and lowering it instead. I chose the latter to save myself the hassle of changing injectors.
I've got the MAP set at 4.4v now and I think I'm getting close to the ideal setting. I'll run it at 4.4v over the next few days and see what sort of gas mileage I get. I'll also check the colour of the plugs when I finish the next tankful of gas to see where I am.

Well guys, my MAP adjuster seems to be working very nicely. Er, no. Actually, it's working even better than that.
I ran my last tankful of gas with the MAP input set at 4.2v and got 20.7mpg. I haven't seen a figure as good as that since I installed my 24lb injectors nearly two years ago! It was from a mix of about 60/40 highway/city driving.
My plugs look good (pinkish/brown deposits on center electrode) and light sooty deposits on the ground electrode. No pinging under WOT so definitely not too lean.
If I haven't yet hit the bullseye with the A/F mixture, I must be pretty damn close!

Gas mileage going up and up!!!

I got 20.9mpg from my last tankful of gas with similar type of driving to my last tankful and the MAP set at 4.2v. That makes my last two tankfuls (20.7, 20.9) about 2mpg better than what I was getting without the MAP adjuster. I'm really happy about that.
I'll try the next tankful with the MAP at 4.1v. I think I'm very near or at the correct A/F mixture now. I definitely won't need to go below 4.0v.