Boost gauge reading Vs. Map Sensor reading
 

I have an 87 TII and i just put in the Rtek 2.1, and i just bought an autometer boost, vac gauge part # 4907, i installed it yesterday and after i was done i went to check what reading it would give me and compare it to the the reading the Rtek gave me on the palm. I start the car and to my surprice, the gauge is reading more vacuum then the MAP sensor... the gauge reads 15... and the MAP shows like 10-12inches of vacuum, any ideas what could be happening? maybe sensor is bad? if so how would i check it? i'll post a pic of the logs and a pic of the gauge later today.

My vacuum readings show a little different from what I know them to be when I monitor them on my palm. The boost readings from my autometer gauge and what I data log match up perfectly however. There is a pressure vs. voltage scale in the FSM you can use to test the sensor.

it's sort of the same case, i went full into boost today, to check how much boost i was running and i was running 8-9 pounds and my friend told me the palm showed the same 8-9 pounds, my main question is pretty much, should i go off the vacuum reading off of the gauge, or the reading on the palm?...

I'd trust a mechanical gauge over an aging MAP sensor. Maybe the sensors are just more accurate under boost than they are when reading vacuum.

If the sensor weren't so old I'd 100% say go with it. But 20+ years changes electrical properties. On a lot of newer cars with on board MAP sensors (STi for example) I always go by the factory sensor reading when tuning.

As well, you've got to take into consideration that the MAP is reading through, say, 3' of wiring, where as the boost/ vac is (should be) reading a direct manifold line.

Because of the inconsistency in vac - which, as RR88 said, is pretty common, I wouldn't concern too much unless you see a SHIT-TON of discrepancy between the two. The fact that BOTH read the same amount of positive manifold pressure is a good thing.

If I had to take my pick out of the two, I'd rely on the gauge for vac (mmHg) and the digital for boost.

ok, so basicly you guys are saying that if i need to make a correction at let's say 4inches of vacuum, at 3k rpm according to the WB02, i make the correction when the vacuum gauge reads 4 inches me the engine is at 4 inches of vacuum although the Map is reading say 6inches?

You'll be better off using one reading the whole time. If you datalog, you'll have map sensor measurements. The map sensor is what the ECU uses to determine vacuum/boost, so I'd adjust at whatever vacuum level that was. In other words, if you datalog a point at 4 inHg, make your adjustment at 4 inHg.

RR88's right: whatever your measurement base, keep it consistent. If you're going to make adjustments at, example, 4 inHg (reading on one unit, or the other) do your tuning on THAT unit, only.

Don't try to figure up the mean average between the two and ping-pong from one, to the other...

Doing that will muck up your dialed in settings and can cause a WORLD of havok.

i'm thinking about just using the rtek readings to create my base maps, and then go from there.. if the fuel ratios are good then cool, but if not then i'll try going off of the gauge and see if that helps, thanks for the help guys, also i have another question for people with the rtek 2.1, i was trying to adjust timming on my car because my car will only start if i advance the timming all the way, i already know i have low compression but i don't want to talk about that, and then after i start the car, then i back it up again, but i noticed that the rtek doesn't see the change in timing, or at least it doens't tell me how many degrees i'm advancing it or retarting it, i only know by the timing gun i'm using. so my question is, since you can only start changing the timing after about 1k RPM's, then i was thinking about advancing the CAS all the way so i can start the engine, and then retard every single value on the timing tables by how much i advance the CAS, what do you guys think?, and i'm going to have to start messing around with timing tables too because my turbo is spiking all the way up to 8-9 pounds and i don't even have a boost controller

Naw. The ECU advances the timing from minus five degrees to plus five degrees WHEN your in start mode. There's no reason for you to be turning the cas to advance it.

The ECU depends upon YOU having initially set the CAS to five degrees before TDC. IF you turned the CAS as an example a whole bunch clockwise and cinched it down, then the ECU is going to assume that position is five degrees before TDC from then on..........even though you Know it's waaaay off from true five degrees before TDC.

IF you have low compression.........then go to the start map and adjust the fuel for starting to a much less figure than the stk setting. But that would be only for a hot engine. A cold engine would not need this to be done.

You need to look and make sure the ECU is seeing the START signal and then see if the water thermo sensor is reading the water temperature. And if those are right, put a timing light on the thing and make sure the timing is right in the first place. This turning the cas to start the car is not something that should ever have to be done......ever.

i see your point, and i totally agree that i shouldn't be advancing the CAS, i'm going to have everything how it's supposed to be today, my idle and my timming and then i will check compression to see what i'm at, if compression is good, then it must be something else

The RTek won't show you it's own adjustments in regard to the CAS, as 'Hailers' explained...

LOL. My first analogy was a scale reading it's own weight.

yes put the CAS back to stock. the whole point of the rtek is so you can change the timing in the software.

as far as the gauge thing goes, pick one and tune to it. whichever is easier.

i have a couple of autometer gauges in the toolbox, and they vary even not hooked to anything its about a 4psi difference between em.

Going to the PALM and reading water temperature is a good place to start. Do that with a cold engine.

IF water temp reads 176*, with a cold engine, that is the problem or a problem. The water thermo sensor is not connected up and the ECU is defaulting to 176*F and therefore upsetting the start procedure.

And try this: Turn the key to just ON. Now turn the Palm on and hit DIAGNOSTICS in the right lower corner. When you do that it will show ERRORS, but right now I'm not interested in that. What you do on THAT page is go to the bottom of the display where you see two arrows one above the other pointing in opposite directions. Hit that symbol. NOW the display will show INPUTS/OUTPUTS.

The second item in the INPUTS is .........STARTER. Now turn the key to START and watch that starter box. It should show a X next to the word STARTER after the engine turns over a few times. IF it does not, then that is another problem. The ECU is not seeing the START signal and that would cause cold start problems and maybe hot ones also. Gotta see the X in the START box for things wto work out right.

Make sense? Are you getting to see that INPUT/OUTPUT display page? IF not I'll try again to describe how to get there.

Damn, Hailers! Bustin' out the Geek Squad advice hot-line!

You used to watch Mr. Wizard didn't you? Huh? Huh? Huh? Yeeeeeeeeeeah.

Gigetty!