still trying to diagnose...

[rb250sx]

Got to work on the car a little bit today, but im still trying to diagnose my idling(well, running) problem. I just replaced the MAF today and it didnt help. I was going to try to test it last weekend, but it wouldnt start with the MAF plugged in anymore. So i decided just to get a new one and try it. It used to start and just run really really rough with the maf plugged in, but now it wont start at all. so this is what i know....

With the MAF plugged in.. -used to start, doesnt anymore - vaccuum used to bounce between 9-15mmHg -ran extremely rich

with MAF unpluged -starts -vaccuum steady at 15mmHg -runs extremely rich

I pressureized the system and it held steady at 12psi with no problems, so i have no leak. Compression test showed ~165 on all 6 cyl. What should i look into next?

[JonPowell]

Check MAF & O2 wiring for continuity & resistance(should be none).

What else have you tinkered with, IACV, TPS....

Is the start signal getting properly to the ECU?

Is the CAS set properly for correct base ignition timing?

Is base fuel pressure set correctly?

[rb250sx]

havent messed with the IAC, only thing i did with the tps was unplug it to try to set the base timing, but i havent been able to set the timing because the idle wont stay sturdy. i left the CAS in the middle for now until i can get it idling sturdy. Im assuming the start signal is getting to the ecu correctly, because it starts. As for the fuel pressure, im going to put the ajustable regulator on right now, i didnt want to change it before because i didnt want to change anymore variables, but ive been told several times the fpr wouldnt cause it to run like that. ill let u know how that goes in a little bit

[rb250sx]

all resistance were 0
Modified by rb250sx at 1:59 AM 6/5/2005

[rb250sx]

got the fpr on, unfortunatley it wont fire at all now, i ajusted the fpr to several differnt points but no luck. unfortunatley the only fuel pressure gauge i have goes to 10psi. I was hoping it would at least fire.

[goofynick6]

You need to know what the fuel pressure is at, with that fpr on there you have no idea what it is at.

Did you pressurize it from the maf back all the way to the engine? Do you have continuity from the maf plug to the ecu? That's key, I had that problem once. When my car idles at 800rpm, I have about 18-19 in/hg of vacuum, so 15 sounds low, unless you're at low rpms (like 600). IAC won't affect things that bad, you can just unplug it for now. Maybe a few missing grounds? Dunno, could be so many things on a custom swap with custom wiring.

NIck

[rb250sx]

yah, pressurized from the maf all the way back, have continuity in all wires. I got the car running again, changing the fpr put way too much fuel in the cyl and fouled out my plugs. So now that the car runs again, i went out and tested the voltages going to the ecu from the MAF. the FSM says ignition on it should be .3V i got 2.63V, cranking should be 1V, i got 2.59V, and idling should be 1.1V, i got 2.47V. I tested the voltages with both the MAFs i have and go approx the same numbers. the maf ground to the ecu is good, and i took those voltages right off pin 27 as well as right where my wires come out of the sheilding. One thing im curious about though, there are 3 wires on the maf plug, 2 go into the sheilding and the other (power) runs outside of the sheilding. when i pull the sheilding apart at the end closest to the ecu, there are the 2 wires and also an uninsulated wire that continues to run to what appears to be a grounding connection down by the ecu. Does this have something to do with the sheilding? I dont know if the increase in voltage is from poor sheilding or what, but it seems strange that i would have 2 bad MAFs that give me the same voltage. btw, i get 12V to the MAF, i know there was a discussion about being 5v or 12v earlier.

[biglipzit]

have you pulled the shielding all the way back to see where this uninsulated wire originated from? I think it may be spliced into the MAF ground wire to add adition ground. Have you tested to see if the wires not being shielded is the problem yet? it makes no sense that when there is no MAF connected to the plug it runs fine. There is some disruption between the MAF and ecu somewhere along the wire and the shielding may be the problem if it isn't continued the whole way like it should be.

[rb250sx]

just pulled the sheilding back, the uninsulated wire doesnt connect into anything, just runs the length back to the maf and stops, im assuming to help the interference, but i tested the voltage going through the wire, with the ignition on it produces .01V and running produces .03V, im assuming from induction from the signal wire.

[JonPowell]

Check continuity on the signal wire(at ECU) and the maf plug at all 3 pins, see if you get continuity to more than one pin. Might have a small short somewhere...

[rb250sx]

Thanks Jon! have continuity at all 3 pins, now just to track down the short

[biglipzit]

wow good thinking jon. Been brain storming about it for a while didnt think of that.

[eh?]

Maf wiring is wrong, sensor power and a ground are switched. If you have a s2 maf swap the outter pins. Check the Wire diagrams for s1 maf.

[rb250sx]

ahha, well heres the thing. I figured the short was in the plug because the hto wire doesnt run together with the signal and ground, so i cut the plug off and tested again, same thing. Im not a genious when it comes to wiring, but when the eccs plug us unplugged the only continuity is to the signal wire, but with it plugged in theres continuity to all wires. But if im correct there should be no continuity with the hot wire without the maf plugged in and no plug on it correct? so it appears theres a short in this circuit in my ecu?

[rb250sx]

Maf wiring is wrong, sensor power and a ground are switched. If you have a s2 maf swap the outter pins. Check the Wire diagrams for s1 maf.

I have an S2 maf. B/W wire on right goes to power, W wire in middle, turnes into W/L wire outside of the sheild and goes to pin 26(ground), B wire on left turns into O/L wire goes to pin 27 for the MAF signal

[eh?]

try switching the wires and see what they read. You did lengthen the wires right? there is a chance they can be swapped.
Modified by eh? at 6:52 PM 6/5/2005

[rb250sx]

the guy i got the engine from had already extended the MAF, but i just swapped the ground and the signal wire because it did seem odd that the ground was white and signal was black, and the s1 diagram said ground was black. tested teh voltages, .5 at ignition on and .8-1.0 during cranking. however the car wont start now haha, could be flooded again.

[rb250sx]

I just want to thank everyone for your help, switching the ground and the signal wire fixed her right up, she sounds beautiful! i can honestly say shes never run better.

[eh?]

:p

[JonPowell]

Awesome, NOW GET A FUEL PRESSURE GAUGE THATS MEANT FOR FUEL INJECTION!!!!!!!!!!!!!!! NOT CARBEURATORS!!!!!!!!!!!!!!!!!

[goofynick6]

Congrats..I knew it had to be maf related..I had a short in my maf wiring and it had the same syptoms. Get the pressure right and you're golden.

NIck

[rb250sx]

Well i guess it wasnt that simple. it would idle beatiful for abotu 15-30 seconds then slowly die dow until it stalled out. i checked the voltage it came up .53 at key on, 1.0 at crank, and then .53 again at idle. so i decided to try eh?s advice and switch the power and ground for the hell of it. well, when i did that the key on went up to 8V so i switched the wires back, and it was still at 8V, at that point i got mad, took my ball and went home. So ill have to mess with it again next weekend.

[USMCgetsome]

just something to try. get it to start and then unplug your 02sensor.

goofynick and i had a similar problem with that. The car would start then get a crappy idle after awhile then die. We unplugged the oxygen sensor then it runs all day but rich.

[rb250sx]

well its worth a shot, but i dont see why that would effect the voltage at the ecu from the MAF. I was just layin in bed about to go to sleep, and its been bothering me so much i had an idea pop into my head that i wanted to run past you. the whole fact that there is continuity between all 3 wires when the ecu is plugged in isnt setting right with me, so if i unplug pin 27(signal wire) from the ecu, the maf will still get power and this should hopefully remove the ecu from the equation of the signal being sent through the wire. So basically my maf will get power and ground, and the only thing ill get through the signal wire is what is being sent from the maf(because there was no continuity when the ecu was unplugged). So if the voltages are right with it unplugged then my ecu circuit is bad? correct? one of those semi-concious thoughts, so please let me know if im right.