grumpy said somthing that made me curious..



how does changing the line to a map sensor effect everything with a SD system? whats the overall effect? could changing the line length effect the "pump shot" making the engine bog with large throttle changes? how sensitive is the setup?

 

The line will absorb some of the "energy" of the engine vacuum the longer the line and softer the material. Thus is will be slower to react and may affect the actual reading if the length is long and made with soft rubber.

Think of it as "sucking through a straw".

 

The MAP sensor and it's signal are critical.
The line CAN act as a filter. ie absorbing the intake manifold's most drastic of pulsations.

There are two ways of handing the extremes, one is with mechanical filtering, the line, and the other in the code.

When the code is running, it samples the MAP from time to time, it's not constantly being used. The code runs in a series of loops, it does something, say TPS AE, and then will do EGR, then Timing, then TCC, maybe MAP lookup, then on and on thur these sections of code.

The MAP signal needs some conditioning to avoid the ecm seeing all the puslations as just chatter, and making huge swings in adjustments.

Some cars, trucks, are extremely sensitive to little changes in the MAP line, while others really don't seem too effected by it.

Yes, it will effect the MAP AE, and how fast the ecm can transverse reading the VE table.

Pep Boys and Advance used to carry the same type small semi hard plastic lines, like GM uses.

 

Then, if I replace a 2mm. wide vacuum line for a new wide 3mm. vacuum line - in a 600 mm. longitude line - I must cut the line to 400 mm., Since:

- Old vacuum volume in MAP line = 2mm. x 600mm. = 1200mm3.

- New vacuum volume = 3mm. x 400mm. = 1200mm3.

(Formulas aren't right but it's the idea).

This is?..


Denis V.

 

Volume change primarily effects the timing, or amount of delay for the MAP to react.
The wall stiffness, primarily effects the dampening of the signal.
They do act in concert.

 

for giggle recently i ran a 15ft 1/4 vac line on a car and stopped the MAP AE and focusosed directly on the TPS AE and using it to my full advanatge., after a bit of tweaking i found the idle to be easier to stabilize and the AE problems that had been noted in the past were fiarly minmal. just throwing my 2cents in there,.

 

Just to further this a bit, I'm figuring that too small a vac line will delay the signal because of impedance to flow, and too large a line could also delay it due to the amount of time for the larger amount of air to move. Am I thinking ok on this? Is too big, AND too small gonna slow down (delay) the signal? Is there any reason someone may want to do something like this? I would think you would want the fastest, most accurate signal you can get.

Just doin some thinking out loud here.

I have noticed that pretty much all of the newer GM's have the MAP sensor mounted directly IN the intake (SBC Vortec, 3800 with the plastic plenum), or at least just connected with a rubber "TEE" (3100 "M")... I gather that this setup would have the quickest response, and no dampning whatsoever.

 

There is no real flow.
More like only a slight shifting of air as it moves back and forth.
Introduce a pin hole, near the sensor and then you have actual flow.

 

So, with a slightly lumpy cam that pulls less vac than stock at idle, would you want to use a longer, softer hose to the MAP to lessen the pulsations?

 

You first want to hook it up with the hard plastic like GM uses. If you're not happy with the results, then you can use the tubing as an attempt to help things. There's lots of variables, on making a sweeping statement may or may not be true for all applications.
The softer hose would dampen the pulsations. Minor, nit.

 

this is really the question i wanted to get to..


if i used a softer hose, and moved the map to the far part of the cowl, and ran a nice long line, would it help even out everything?

 

You can quite easily over dampen the signal.

 

how would i be able to tell if im overdampening it or not?

i have a TBI computer, so the refresh rate is REALLY slow to see...

id just want to dampen the pulses out for a smoother idle...



is my only option to do trial and error with diffrent lengths and hose?

 

yep

 

Yes, the display rate is quiet slow and limited in information. But the ECM clock speed is faster than the display. That is just the communication speed with the ALDL port.

I woudl say that you would "hear it" much sooner. Sometimes, these "scan tools" make us forget our other senses that "tuners and mechanics" used in the good old days.

No scan tools, no wide bands, no EGTs...just plugs, a stopwatch and a good nose and ear.

 

Along with the ever important 'glutinous maximus' instrument.

RBob.

 

When you go too far it will be apparent.
Refresh rate has little to do with it.
There is no guarantee this will improve your idle.
Yes, you have to use all the tools and techniques available to get the best possible results, there are no silver bullets.

 

So is hard plastic line bad?, like the kind that you get with aftermarket gauges? Because that’s what I am using. It is a lot smaller opening then the stock line used. That may explain my stumbling / stalling problem at idle-low rpm’s.

 

I think something was missed when it comes to lumpy idles caused by longer duration higher lift cams. No length of vacuum line, short or long, will make up for low vacuum at idle. This can only be taken care of by taking fuel and timing out by reprogramming the chip to account for the changes. Now once you are off idle, either crusing or accellerating, the map would come into play as far as having a greater roll in overall opperation of the engine.

Steve

 

I can see a wrong idea about the soft vacuum hoses.

I used light blue silicone soft vacuum hoses (very nice and beautiful in the catalog's pictures), but the only that I got was COLLAPSED vacuum lines when the engine was hot = 0 (zero) vacuum to MAP, bad idle, bad power, waste of time , waste of money and GRRRR! with this job (I went back with the original vacuum hoses).

Since You can't controls the engine compartment temperature, you can't controls the more or less "soft" vacuum hose.

For me, the only way for MAP signal control is via EPROM + a short hard vacuum hose (It's only my opinion).

 

That would be my preferene also.

As I recall, this was Bruce's original cavaet when the topic originally began in the other post. This post was more of a discussion on the possible effects of what happens when you use a longer and/or softer piece of hose.

Your experience with that "pretty blue hose" is a good point on what may also happen when things get heated up under the hood should you attempt to use a "mechanical" method to cure an eprom related problem (due to low vacuum). You may encounter further problems (if you don't notice that pretty blue hose collapses when hot).

 

Nope, tis a different topic. This thread is about effects of lenght of MAP sensor line. It's something the non code guru can do to aid in tuning.

Using a rigid line and tuning the filtering rate in the chip is the best answer, but not always can we avail ourselves to the best answer.

 

I don't see why it wouldn't work.
Stalling isn't what I'd expect to see as a problem from MAP line size.
Off idle and transistional problems are what I've seen most often as problems.

 

I guess I should have directed my reply to va454ss and Mr. Dude. I still don't think the length of hose would have any affect on idle quality.

And as I should have said in my first post that off idle to wot, the length of hose my make a difference in overall engine operation.

Steve

 

This can only be taken care of by taking fuel and timing out by reprogramming the chip to account for the changes

You also said that to make it idle better you should take out timing and fuel. Now it's just my method of tuning lopy cams but I have found that adding timing and fuel will even out the idle not the opposite. But again, no one is trying to add vacuum by using different length and hard lines. What is trying to be accomplished is reducing the amount of erratic map readings that you get from lopy cams. It's the reversion in the intake that causes the fluctuations and you are right, no amount of vacuum line can get rid of it but maybe you can dull it enough so the sensor doesn't pick it up as much.

 

I need to be carefull when I make a blanket statement as I did in my first post. I can see where you might want to add timing and fuel to a carburated setup, but I was under the impression that the computer added fuel when a low map signal was incountered. Now I know the tps and rpm play a role in all this as to what the ecm will give the engine as far as timing and fuel. I have heard so many times that when someone swaps in a cam with a slightly lumpy to very lumpy idle, before tuning, that the engine runs rich. So if I'm not totally screwed up that is what I have bassed my assumption on. I hope I havent left everyone scratching their head.

Steve

 

Maybe thats some of my problems with my hotcam and SD with my relocated MAP.