I built a 4.7L stroker about a year ago and it runs great. I went with the 30Lb ford performance injectors and a Clifford header as well as the Crane low rpm cam. It has the Renix computer. I finally got around to letting the State of Colorado have a look at the configuration and bless it. They passed the visual portion but when the tailpipe test came up, I read about 50% high on CO, both at an idle and at 2500 rpms.

When I built it, I used all new sensors. I'm an electrical engineer, so i just built an adjustable voltage source tonight for the MAP sensor and cranked the voltage down from 5.0v to 4.0v. Does anybody have any experience in tweaking the MAP? Did it help? How far down did you have to tweak it? I get one free retest, then it is another $25.

That adjustable MAP will help you fine tune the fuel delivery but without an air/fuel ratio reading you're just guessing. Not a bad investment to make and you can get one for about $75 last I checked. A lot of guys running strokers run the 24lb/hr injectors without any MAP tweaks.

It's been a while since I built it so I went back and looked at my records. I am running the ford performance 24# injectors. I built the MAP adjuster last night and adjusted it this morning. Passed with flying colors. This should also help the mileage a bit as well.

Don't really know why it didn't pass with the stock map. All the sensors are less than a year old. Maybe the low rpm cam with its overlap contributes. Maybe it is the extra resistance from the snorkle when not moving, but any way, its fine now.

your injectors are rediculously huge. go to 24lb

Hey Sundowner, read the last post a little closer. :smokin:

You might still want to get an A/F ratio display to make sure you don't lean it out too much and burn up your valves.

I set it up with a tail pipe analyzer. I will monitor the plugs.

What voltage did you set your adjustable MAP sensor to get it to pass Colorado emissions?

so you basicly duck-taped a lm317 to your MAP and solved your emission problems?

Hey, I'm a EE, I resent the duct tape remark. I fab'd a nice box with a disconnect switch, a pot, some caps, resistors, a heat sink,............................................. ..and an LM317.

I'm still screwing with the voltage but it appears that it will be around 4.6-4.7v. Heck I could have done it with a diode in series with the supply lead.

Hey, I'm a EE, I resent the duct tape remark. I fab'd a nice box with a disconnect switch, a pot, some caps, resistors, a heat sink,............................................. ..and an LM317.

I'm still screwing with the voltage but it appears that it will be around 4.6-4.7v. Heck I could have done it with a diode in series with the supply lead.
Hey, I'm just a Carpenter. Your injectors are to large. Even if you turn down your fuel pressure and bring your pulse width to an almost trickle. Your still to rich... Unless of course your running 10.5:1 pistons with 245 degrees intake duration @.050.
And I haven't switched, I don't do POT, Just drink Tequila....

The problem isn't that the injectors are too large. With the increased compression (9.6) and the increased displacement (4.7L) more fuel is needed than the stock 19# injectors can provide. The problem is that the fuel air curves and how they translate into injector pulse width, that's stored in the computer is not accurate for this compression or displacement. The key is to trick the computer into giving out the correct signals for this setup. Skewing the MAP sensor signal does the trick.

Yes, the computer is supposed to compensate, but the thing is that it is only designed to compensate within a finite range. The new parameters are outside that range.

Tom's got this stroker thing down pat. He's right on with the injector size. The Renix system doesn't have an O2 sensor so the PCM does not "learn" as well as a OBD systems. So for emissions purposes, he has to watch the MAP sensor to tweak the fuel/air mixture. Very common tweak for any 4.x stroker.

Tom, congrats on the emissions sticker!

The problem isn't that the injectors are too large. With the increased compression (9.6) and the increased displacement (4.7L) more fuel is needed than the stock 19# injectors can provide. The problem is that the fuel air curves and how they translate into injector pulse width, that's stored in the computer is not accurate for this compression or displacement. The key is to trick the computer into giving out the correct signals for this setup. Skewing the MAP sensor signal does the trick.

Yes, the computer is supposed to compensate, but the thing is that it is only designed to compensate within a finite range. The new parameters are outside that range.
Sorry Tom:
I don't buy the "If you can't dazzle em with brilliance, Baffle em with bullsh**" I'm not trying to pick on you but, Look at the percentage increase in your displacement VS the percentage increase in your injectors. There's now a huge imbalance. Even if you got your smog, The motor will have much better performance with a smaller injector.
Have you run Datamaster software with a laptop connected yet? I'm not sure if your ECM's been hacked yet. It should be much easier to tune with 24 lbs.
I run 21 lb. injectors at 47 PSI and my cylinder volume is 41.45 Cubic Inches, or 679 Milliliters. Compare these numbers with yours and I'm sure you'll see your to big.
When you tighten the Pulse width, you lose the atomization and it ends up being a trickle. This gives poor performance and gas mileage.
Again, Just an ol' Carpenter....
Instructor.

OH yeah! almost forgot.. I run 9.8:1 compression with 210 degrees duration @.050 with a 480 lift hydralic roller. My Tuned Port Injection will run up to 5500 RPM. All with 21 lb. injectors.... We'll I might be runnig closer to 49 lbs. at the fuel rails?

MrWillys, I don't have the formulas here at this computer but the renix system and the OBD-I system use a fuel pressure of 39 psi vs. 49 psi with the obd-ii systems. Given that information the actual fuel flow with the 24lbs'er @39psi is within an exceptable range for these engines.

You did catch the correction that he was running the 24lbs ford injectors and not the 30lbs, right?

You did catch the correction that he was running the 24lbs ford injectors and not the 30lbs, right?
Sorry, but I missed the correction. I was wondering how the heck the thing was running with 30 lb. injectors....
When you say OBDI runs 39 psi at the rails, you're talking about Dodge? Cuz, GM OBDI has several different pressures.
Sorry for MY confusion....
Scott

Sorry, but I missed the correction. I was wondering how the heck the thing was running with 30 lb. injectors....
When you say OBDI runs 39 psi at the rails, you're talking about Dodge? Cuz, GM OBDI has several different pressures.
Sorry for MY confusion....
Scott

Yeah, jeep. 4.0L stroker motors (4.6L-4.7L)

there are several people who use the 30lbs injectors without a problem but the 24lbs is just about right.

The real advantage of the ford 24# injectors is that the dispersion pattern is much better. I always love the comments. I've heard them all. I built my first engine 42 years ago. I've been building them ever since for various vehicles, buggies, racecars and such. I actually built a land speed record piston driven engine for Stan Barrett and ran it at the salt flats in 68. Back then, doing over 200 was a big thing.

I do all that for fun. In real life I'm a EE/CS/ME and a tool and die maker, so I kind of know my way around design and building. The computer programs that build a virtual motor and give you the specs are nice, but I work from experience, not what some school taught engineer thinks it should be. It's funny how the newer crowd has forgotten how to read a set of plugs or sniff a tailpipe. Without out a tool they can't tell if they are running too rich or too lean. Damn, how did we ever build engines without all this new crap???????

Damn funny thing that my stroker runs 9.6+ comression and runs on the shitty 85 octane fuel around here with no pinging, even when leaned out.

As a note: The Renix system does use an O2 sensor as well as a map and a fuel charge temp sensor.

My rig is ported, larger valves, volume matched, and is running Clifford headers with 2.75 pipe, full flow cat and magnaflo mufflers. It does flow a little better than a stock setup.

Tom:
I'm not quite as old as you, but I do love the old straight 6. I do love the smell of a fine tuned tailpipe, but the electronics make it so much easier. I remember a HotRod article in the 70's. A guy was running a 292 Chevy straight into the 11's in a Camaro. Also, I've had a 67 Camaro and a 90 Ford truck with a 300 inline. These where some of the best cars I've owned. I'll bet yours puts out quite the punch. Glad you were able to resolve the issue.
Can you burn your own EEPROMS with this system?
Scott

I've not been able to find any internal info on the Renix. There is a serial port of some type on the ECU, but don't know the buad rate or even the levels. I would love to reverse engineer the system if I had a bit of info to start. Right now building a new front axle is taking my extra time and getting ready for the ColoradoFest 2004 sponsored by NAXJA. I have the horrible responsibility of prerunning all the trails to make sure of their status.

Tom Houston
President - NAXJA Colorado Chapter