Well, it seems that I have made a mistake on my truck. I sure do miss the "diode wire" that I had on my MAP sensor signal wire.

I drove the truck empty for the first time in a long time. I've been hauling the horse trailer around for the last few weeks and yesterday finally got a chance to "relieve some tension" if you know what I mean. I usually take it really easy while pulling the trailer to help the tranny live.

Seems that the 1.0 exhaust housing is murder on from-a-stop acceleration if the PCM sees no boost. It adds ZERO fuel for about 6 seconds......YUCK!! I'm sure the annihilator is great for stock applications, but holy cow it sucks with the big exhaust housing. The "diode wire" at least made the PCM think that there was boost when there was none and I'd fuel like a mad chief from a dead stop and get boost immediately. Like I said, now I have to wait 6 seconds before I spool....I can't even powerbrake in "stock" anymore it's that big of a difference!!

Anybody know the specs for the diode wire? I gave mine away to the guy I installed a DP Tuner for a few weeks ago......when I got the new annihilator. If anyone knows what wattage I need, I'd appreciate some info!!! Thanks.

 

I'd start with a search of the term "zener diode", as I believe that's what the diode is. Since I don't use this, I have no idea what the value should be, but it would be just under what the maximum input for the PCM would be before defueling.

It allows the normal voltages to be seen by the PCM up to the value of the diode, then the curve will go straight-line at that point, with no additional voltage to cause defuel.

Zener diodes are rated in both voltage and wattage, so find out both ratings before you go looking for one.

There'll also be a resistor involved in this, and it, too, has two ratings you must know. Resistance (in ohms), and wattage.

Pop

 

This is an excellent description of how an "ideal" Zener diode would work, and if a real one worked like this it would make a dandy solution to stop the PCM from de-fueling at about 22 psi of boost. In fact, the Zener diode was the "Banks solution" to avoid the SES light due to over boost back in the 1999-2001 time frame, but it has since been discontinued because of the adverse effects on performance including reduced mpg.

I'm not sure how the pic of my attempt to show the difference between an ideal vs an actual Zener diode will come out until after it's posted, so I'll describe it as well. As SpringerPop said, an ideal Zener diode will ..."It allows the normal voltages to be seen by the PCM up to the value of the diode, then the curve will go straight-line at that point, with no additional voltage to cause defuel"..., and this is the top curve in my drawing. The lower curve is how an actual Zener diode performs, and as you can hopefully see in the pic, it starts to limit the boost signal to the PCM at lower values of boost pressure before the troublesome threshold of 22 psi boost is reached. This means that with a Zener diode installed, the PCM can no longer see the full boost that's occurring at levels below 22 psi, and this screws up the PCM's ability to properly fuel the engine at these intermediate levels of boost, and this in turn results in adverse effects on performance including reduced mpg.

The real problem is that the 22 psi threshold for de-fueling is in the PCM firmware, and this can't be modified by the programming on a chip. Therefore, the only way to run at boost pressures higher than 22 psi and not trigger the de-fuel limit inside the PCM is to physically limit the boost signal going to the PCM. It's my considered opinion that whether this limiting is done with a Zener diode or with some kind of pressure relief valve or regulator, you will incur an unfavorable "pre-limiting" action like I just discussed for the Zener diode approach. Using a simple diode or a mechanical pressure device, you can't make an actual limiter that works like an "ideal hard limiter", it just can't be done period. However, if one wanted to employ modern day electronics, one could design an "electronic black box" that could be installed between the MAP and the PCM that would be a very close approximation to a hard limiter.

 

The drawing came out well gene. I was considering this route until i heard all the bad about it. cletus some new tuning may help that lag on the line, and keep all the other benifits of the OBA.

 

Gene mentioned to me that moving the MAP sensor input from the cool side of the compressor manifold, to the hot side of the compressor manifold will help some because the boost is built first at the outlet of the turbo. I also drilled and tapped it in a location so that the air coming out of the turbo has a "ram air" effect on the gauge, as the location i have it is right at the turn at the inlet of the compressor manifold. I tapped my boost gauge for that as well, and capped off the existing MAP line elbow for use as a boost reference for my fuel pressure regulator at a later date.

 

4.7 volts.

 

We'll call this one the "Strokin pipe".

 

I'd like to see data for boost gauges hooked to both locations, because comparing those readings will allow an estimate of air flow (cfm) into the engine using published data for the pressure drop across the IC vs cfm flow through it. Even better, you could get a 0-5 psi gauge, and measure the differential pressure directly. Next time I'm getting work done at a specialty shop, I'm going to see if they'll drill and tap and install fittings so I can hook up a differential gauge to compare to the one I use at my air filter box.

I'd also like you to take some data of boost vs exhaust backpressure as you pull some of the grades in your area. Your turbo is more efficient than the one I'm trying to model, but such data would still be of interest.

I know you use a pressure regulator to control the boost pressure to the MAP sensor, do you have any data on the "pre-limiting" action of that regulator? Based on its size, it uses a fairly small diaphragm to sense the input pressure, and this means that it's got to have some degree of "pre-limiting" action as the input pressure approaches the 22 psi threshold. As a comparison, I've given a pic of my custom configured pressure regulator, and you can see how much larger that diaphragm is. A larger diaphragm reduces the "pre-limiting" action because in response to a given pressure change, it generates a much larger force to overcome the adjustable regulator spring, and this allows the regulator valve to remain wider open, and then snap closed just as the threshold pressure is reached.

BTW, if any RVers are reading this, over the years I've developed the ultimate regulator to control the water pressure going into the RV. I've combined a custom pressure regulator and relief valve combination, and can provide part #'s and the adjustment procedure to interested parties.

 

Jeez!! Thanks for all the replies, guys. I guess my main issue is the low-boost fueling and for some reason the "zener diode" really helped it out a bunch.

As far as the reduced MPG goes, I have yet to see that as I was able to achieve 20.5-22 MPG with it and about the same without so far.

I'm going to go play with the scanner for a while and see what I can come up with.....

 

I'm not sure how a Zener diode increases fuel at low boost, because there it should have no effect at all. It would seem that you'd have to trick the PCM into thinking there was more boost than the MAP sensor was detecting, and this would require adding voltage to the MAP output, not clamping it to a maximum value which is what a Zener diode tries to do.

Maybe you're saying that whatever you're using in place of the Zener diode to limit the boost from the MAP sensor to the PCM is reducing the boost signal at low boost, and the simple test to see if that's what's happening is to remove the device and do a test without it.

 

Here's what I did:

Removed Zener Diode and gave it away.

Installed ITP Overboost Annihilator.

Noticed no fueling at low boost now.

Annihilator working as designed (regulated shop air in @ 40 PSI =21 PSI out).

Maybe I is just stoopud.

 

Gene that is quite a setup there. Is that appendage sticking up on the right between the hose and the regulator something to absorb water hammer?

 

Yeah, and I don't see an inch of duct tape anywhere, so I know he hasn't finished with it yet.

 

LOL

 

All the Zener diode installations I've seen used crimp type connections to the MAP sensor wires. Is it possible that when you removed the Zener diode you messed up the connection from the MAP sensor to the PCM so now the PCM isn't getting a good signal from the MAP sensor?

I'd be interested in your measuring psi IN vs psi OUT for some input psi values in the range of 0-20 psi to determine how much "pre-limiting" action that regulator has. Your regulator might not be passing the lower pressures to the MAP sensor. Like I said before, replace it with a piece of hose and see if you notice any difference.