hosrom_951

Either there is something wrong with me or there is something wrong with various rennlister......seriously

With all the comments on "use the search" i did, and came up with a LOT (and do mean somthing like 15+ rennlisters) that don't use resistors in Siemens and Bosch injectors (seriously)

Andy: Remember when you posted a pic of you're catch cat on the 944 general board? a rennlist member asked you why do you have resistors on the firewall, and you said that you don't need them and you do since you are running sequential (im no familiar with types on injectors there are).

Look at my posts with regards to injector brand and resistors, i and several other rennlisters also mentioned that you don't need resistors for Siemens and Bosch brands.......

Boostguy: If you could afford $60 per injectors, i believe 20 cents is also affordable

Samgrant: What is wrong with Anderson Motor Works?? (seriously)

Matt H

Hos -
I am not saying that running without them is 100% safe, in fact it probably isnt. However, there are a number of people I know who do not. Some of those people are FAR more knowledgeable than I am.

As to Anderson, I have no personal experience except for knowing John from a LONG time ago on the old old old email lists. If you look for user Dave and Anderson you will find a really ugly story.
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Bengt Sweden

The injectors operate at the same frequency regardless of throttle. The biggest draw is to open so there wont be much difference between wot or pt.

How much research do one need before investing 20c?

Bengt

SamGrant951

Hosrom - Ill pm you, but the search function is a marvelous tool! -hinthint-

OriginalSterm

12 ohm resistors are saturated switch, meaning the same current should be applied during the entire duty cycle. Lower impedende injectors are typically peak and hold injectors, that means a larger current is sent to the injector to open it faster, then a lower current is delivered to hold it open for the remainder of whatever the duty cycle may be. For example, many peak and hold drivers that I used were 12.5A peak, 5.5A hold. I do not know what specific injector driver our car uses.

You can run each style the wrong way, but the spray characteristics (particle size, spray cone, response time, flow per pulse, etc.) are all changed.

From designing, building, and testing fuel injectors from Bosch, Siemens, Denso, and Delphi, I can tell you an injector should be run in the manner it was designed for. Will it work when used other than recommended? Yes, but the performance is not optimal, nor is the life expectancy of the injector. My professional (I use the term loosely) recommendation is to target the 5.5 ohms the injector drivers are expecting.

zerMATT951

badass951 wrote: I really don't want to fuel the fire here but because I've *also* taken many electronics classes in my past, I feel like there's one simple fact missing here... *nobody* on this list has any idea what the engine computer can handle when it comes to current. To make the statement that 2.18amps is normal, and therefore the computer will "fry" at 4.29amps is rediculous. I doubt anyone here has tested the Porsche computer to find out what output current it is truly capable of, or called Porsche and asked for that matter (not that they would tell us anyway).

Any of us can do simple math and see that the current draw will be different, but that doesn't necessarily mean that it will be an issue.

Seems to me that real world experience speaks the loudest in this case. We're here on Rennlist with a BUNCH of people who have upgraded injectors and there's only ONE case of someone who has blow their computer? Isn't it possible that their computer was faulty to begin with (bad solders are VERY common in these things) and that the extra current draw flushed out the problem and finally fried it?

For what it's worth, I'm in the same boat as everyone else though. I've read both sides, and I still don't know whether I'm going to bother with resisters and hacking up my wiring harness to do it ($0.20 or not). I've got a set of flow-matched 55# seimens ready to go in once the head gasket is back in place... I'll have to decide pretty soon I guess.

evil 944t

I have had know problems with mine and its been 2 years. I have had those resistors on my kitchen counter for ever. I'm to lazy to install..... hee hee

TurboCab

Hey:
The use of resistors is not dependand on injector brand! This is an injector/driver (ECU) design issue. My advice is to meassure the resistance across the factory injectors and use injectors with similar resistance value. If the factory injector is 5 ohms or less can be called low resistance, if it is more than 7 ohms it is a high resistance injector. If the factory injector is a high resistance and your replacement is low resistance you must use a resistor to low the current load on the driver.

pk951

Well let me jump in here and say i am running 55lbs injectors without resistors for about a year, so far, so good, dme has not fried yet. But everybody says you need resistors with those injectors time will tell.

I know of one rennlist guy that was running 75lbs without the resistors in 100 deg-heat no problems.

hosrom_951

Anyone has a pic of just where exactly they installed resistors?

badass951

You are correct, however I think the Siemens high impedance 55 lb/hr injectors are calibrated the same as the low impedance. In most cases though this is not the case. I may be wrong though.

I did some research and could not find the amount of amperage the DME can handle. However, you must admit that as a general rule, if a system was designed by the factory to handle 2.18 amps for the injectors, then almost doubling that amperage is not as safe as the recommended amount.

If it means anything to anyone, a lot of people respect RC Engineering and they recommend high impedance injectors.

NZ951

Hosrom, my resistors are setup for sequential injection. Thats why I have 4 and not two.

hosrom_951

Like i said Andy, i am not familiar (sequential) nor the difference between injector types

Do you have pics showing where the resistors connect to? (which wire)

NZ951

The resistors just go in the line to the injector plugs obviously. I have 4 for each injector, opposed to 2 wires into one resistor. I am not sure how else to describe it. I dont have a pic other than what you have already seen. Like LR said, you dont need resistors, so you may not need to worry if you take their advice and get some from them.

hosrom_951

Do a search on "resistors", and look at what you come up with with how many vendors advise on not using resistors, since you are picking on LR alone.