ohh i understand now. can i use an 87 TII ECU on an 88 TII ? DOes the 88 have the high impedance injectors and if i use the wrong ECU wont it burn up?

 

and let me ask this also. About how much power would i lose and how much would my gas consumption go up if i ran 13v all the time?

 

Yes, use a 87 ECU on a 88 is just fine. The early series four ised low impedence injectors, but the key to this is that they use a 6 ohm resistor in the circuit prior to the ECU. So you take the 6 ohms and add it to the resistance of the early injectors themselves and you come up with eight or so ohms. Now the later/newer cars came with no resistor in the circuit, BUT those injectors are about 10-12 ohms themselves. So you can see that the ECU has nadda to do with it. It won't burn up. Trust me.

I run two 87 turbo cars. One is orignnal....the other is a non-turbo conversion. I have no fuel pump resistor relay circuit in that car. I don't notice any significant difference in gas gulping b/t the two. In other words I see 13 plus volts all the time with that car.

On THAT car, at idle, the afr will be something like 13.1 afr. If I pull the wire out of pin 3D while its idling, the afr will change to something like 12.8 afr. So the voltage will make a car a touch richer at idle. I can compensate because I have a variable resistor that I can turn to lean the idle afr out to just about any darn place I want it.

 

well what do you think i should do?? try the 87 ECU or go with the 88 and just cut 3D. I would rather go with cutting 3D i just didnt want 7MPG but since you dont think it will hurt my MPG that bad and you have been right about everything else. im going to go with your suggestion.

 

double post

 

Which is determined by a spring inside the FPR.
But, it has been brought to my attention by a friend, that FC FPR's are rediculously small. And when fuel flow is increased, the stock FPR just can't bypass enough fuel to keep the pressure down. And since I have a Walbro 255, my pressure is most likely higher than stock.

 

That isn't really a problem, it just means your mixtures will be a little on the rich side. An adjustable FPR would let you fix that, but a fuel controller would do the same thing and allow far more tuning scope as well. I'd consider that a far better value-for-money mod.

 

If it were me......I'd put a meter on pin 2B and monitor that to see if its voltage was climbing as I drove down the road and especially when getting into boost. In the next couple of days I'll put two meters on my car. One on the 2B and the other looking at the fuel pump voltage. I'll let you know just about where(rpm/boost pressure) the ground is taken off the pin 3D

I'd also not have any problem with cutting/pulling out pin 3D to make the pump voltage go up. It NEEDS to be up when boosting. I'd never sleep well at night though til I know just why the ECU isn't removing the ground from 3D.

 

Hailers, in my testing after the rewire the relay switched at ~3psi boost, which is the figure I always quote. But more likely the ECU increases the fuel pump voltage based on airflow rather than manifold pressure. It just so happens that particular airflow on my car was at ~3psi, and I don't have an airflow gauge on my dash, only boost. If you get real keen, see if there's a more solid relationship beteen airflow and the point at which the voltage changes.

 

yeah im going to pull pin 3D out today just to make sure my car has the fuel it needs at all times, regardless of fuel consumption. and i suppose while i have my ecu uncovered i will probe 2B to see what i get under boost. i have also got to change over my water thermosensor today because my car is having trouble starting while it is cold.

 

hey i have the plug off of my waterthermo sensor and was wondering if there was any way to use a DMM to test wether or not the wires coming from the plug and going to the ECU are broken. I can use a DMM pretty well but i dont know **** about electricity

 

i just swapped ECUs to see if it would up the voltage under boost....it still wouldnt up the volts so ive swapped the boost sensor and the ecu and still nothing. Its got to be the relay that is the only thing left that i havent swapped out.

 

OOOps! It seems I've fouled the water here. I went out and put a MIttyVac on the boost sensor and monitored the voltage at the fuel pump. Hmmmmm, still 9v when I've put 10psi on the sensor. Errrr, ahhhh, I went and read the Relationship chart in the 91fsm and lo and behold......what causes the change in voltage at the fuel pump is everything but the boost sensor. Oh well. What effects it are the Airflow Meter, intake air thermosensor both afm and engine, crank angle sensor and the list goes on and on and on and on and nowhere to be seen is the boost sensor.

Just shoving the vane in the afm by hand does squat. It seems to be a combination of several things including the engine actually running, so I can't shove the vane back with the engine running and see the voltage rise (I tried a real fast shove but the engine died before any change in voltage).

The water thermo sensor is a breeze. Connect its plug. Then go to the ECU. Get on pin 2I with the positive lead and put the negative lead on a good ground. With the key to ON and the engine hot, the reading in volts will be about .5 volts. It'll vary with the temp of the water. In the summer I'll see it drop down to around .4 volts on a hot day over 100 degrees.

I really can't figure out why your voltage does not change. Yeah, go for the resistor relay since you changed out the ECU and that did not work. Somehow the resistor relay package does not make sense, but I could be wrong. And keep that pin 3D disabled if that does not fix the problem.

Maybe tomorrow I'll get on the output wire from the afm, pin 2E, and see just where/what voltage the transition happens. And by the way, while driving I did notice that the transition to 12v on the fuel pump does happen just about at 2 to 3psi boost. But like NZ said....its more airflow meter related than boost pressure related. I'll post that relationship chart again sometime soon.

It's the *0* that count. The *X* don't count. And don't pay attention to the red marks around the pressure sensor. That was for another post from the past.

 

well right now im running with pin 3d disconnected and the extra 2-3 volts at the fuel pump make a WORLD of difference. my boost used to fade out about halfway up the stock guage and my car never ran "RIGHT" but now with 12-13v on the pump it runs like a champ. i mean i would like to know why my voltage isnt bumping up, but it really doesnt bother me as long as i can get 13v there somehow. ANy more help would be appreciated but im soo happy as it is right now.