Distributor 5V Signal - Help

[ghettosled]

ok, i am reaching out to some fellow experts.

have a truck here and i cannot get it to electronically advance the timing w/ the stock computer. Ran great for several weeks on fully built motor package.

Basically tan wire connected or not it has no timing (as if the wire was disconnected) According to the manual, the tan wire should flash 5.0v from the ECU when the RPM signal reaches a certain RPM.. Basically just as it starts to run. I verified this on some other trucks and it flashed 5v for a second then the timing advances and it runs fine.

This truck will not fluctuate any voltage when cranking or running. I have checked at the ecu as well as the black connector, and ran a new white wire from the ignition module to the ecu as well (i believe this tells the ecm what the rpm is and i would venture to say the ecm doesnt know what the rpm is therefore not telling the distributor to switch out of cranking mode and into run mode with advanced timing.)

I have swapped 3 distributors (one is now running fine in another truck), ecu, chip, etc.. everything but the harness. I have looked at all the pins, made sure they are pushed forward, cleaned with contact cleaner etc. And i have visually inspected the harness to the best of my ability while still in the car.

One thing that may or may not be noteworthy is i can no longer get Datamaster to connect on this truck, and the customer pulled the check engine bulb for an emissions test or something (so it does not function) just prior to the problem. He also replaced the cigarette lighter.

if i manually advance the timing @ the distributor it seems to run ok (just has a hard time cranking over and starting) but otherwise revs clean and sounds normal.

So what i really need to know is what produces that 5V signal that ultimately advances the timing through the tan wire?

thanks in advance. Rarely do i get stumped, especially when i have plenty of parts to swap and figure out the problem through process of elimination, but this one is a PITA... Probably something stupid that i am overlooking, who knows......

 

[MikeRenz]

Re: Distributor 5V Signal - Help

have a truck here and i cannot get it to electronically advance the timing w/ the stock computer.

can no longer get Datamaster to connect on this truck,

pulled the check engine bulb for an emissions test or something

He also replaced the cigarette lighter.

sounds like he cut/pinches/stripped/shorted a wire when removing the bulb or changing the cig lighter. It can't be coincidence that he pulled stuff out and now electronics aren't working.

have you tested the resistance of the tan wire end to end

 

[Foot Performance]

Re: Distributor 5V Signal - Help

I had a smilar problem on a v8 pickup once I ended up running all 4 new wires.

I was reading in the GM manual it says if your tan wire is un hooked it should set a code 42

The purple and white wire(these colors are from a 93 typhoon book) should be the RPM referance to the ECM. To me if there was a problem here it would not start but maybe if the wire is pinched that might cuase it.

The book says if the ground black and red has high resistance this could cuase poor performance so to me if the ground wire to the distibutor has high resitance this would let it run just not very well. The wire does ground in the distibutor so since you changed that I would say you are good internally

I woudl use a headlight bulb and do a voltage drop test fon the wires from the pcm to the dist. I have runn into it multiple times that if you just check with a ohm meter you may get a good reading but the wire is pinched or somthing

 

[ghettosled]

Re: Distributor 5V Signal - Help

sounds like he cut/pinches/stripped/shorted a wire when removing the bulb or changing the cig lighter. It can't be coincidence that he pulled stuff out and now electronics aren't working.

have you tested the resistance of the tan wire end to end

checking the tan wire voltage at the ecu connector, thus eliminating the wire completely. It is not getting the switched 5v signal from the ECU.

 

[ghettosled]

Re: Distributor 5V Signal - Help

I had a smilar problem on a v8 pickup once I ended up running all 4 new wires.

I was reading in the GM manual it says if your tan wire is un hooked it should set a code 42

The purple and white wire(these colors are from a 93 typhoon book) should be the RPM referance to the ECM. To me if there was a problem here it would not start but maybe if the wire is pinched that might cuase it.

The book says if the ground black and red has high resistance this could cuase poor performance so to me if the ground wire to the distibutor has high resitance this would let it run just not very well. The wire does ground in the distibutor so since you changed that I would say you are good internally

I woudl use a headlight bulb and do a voltage drop test fon the wires from the pcm to the dist. I have runn into it multiple times that if you just check with a ohm meter you may get a good reading but the wire is pinched or somthing

yeh i am aware of the code 42 issue and did the entire diagnostic test per the service manual.. Keeps saying ignition module, but we tried that a few times. We also ohm'd each of the 4 wires from the ignition module, and they seemed to be perfect.

What really baffles me is the datamaster thing.. I thought the ecm just needed to be powered up in terms of conenction.... This truck always had a connectivity issue @ wot , however i fixed that by bypassing all the harness and connecting the serial data wire right at the ecu, and the ground to the ecm case.

again, thanks for the imput and taking the time to help.

 

[The_Bronze]

Re: Distributor 5V Signal - Help

The short answer: The PCM produces the 5V bypass signal that travels to the module over the tan/brown wire

The long answer: The ignition module sends the reference signal to the PCM when the engine starts to crank and of course run. The ignition module receives this RPM information from the pick-up coil in the distributor and sends it to the PCM on the REFERENCE line (ppl/white wire). When the engine speed is under 200-400rpms, the ignition module (ICM) grounds the EST signal (white wire) and controls timing. There is usually still a squarewave (that mimics the reference signal) but is at a very low amplitude (less than half a volt). The ECM sees the low engine speed and does not send a 5V signal to the ignition module.

As soon as it exceeds 200-400 rpm, the ECM will apply the 5V reference to the BYPASS (tan/black wire) line (This line should not "flash". as long as the timing connector is connected and the engine is running over 400 rpm - the line should maintain 5 volts). The ignition control module should then "unground" the EST signal and the PCM will now control ignition timing.The EST wire should then have a nice 5V squarewave displayed. NOTE! IF the vehicle is running it is not likely that the white REFERENCE wire is at fault

TEST: Engine running at idle, check 5V at module. If it's not present check for 5V at PCM. Check voltage at REFERENCE wire. Should see a small voltage, probably 100mV or so.[/U][/B]


Both a open or grounded bypass line or a grounded EST line will cause both a code 42 to be set and prevent the ECM from controlling timing (Advance). I would be using a scope, but a quick ohm check of the two lines with the harness disconnected from PCM and ignition module (to ensure they aren't open) and then with one of the leads attached to a ground (to check for a grounded wire). Of course, so will a funky ignition signal from the stator to the ignition module, a bad module, and a bad ECM. There isn't much else left outside of weird tuning issue. The ohms test isn't the best to use, but outside of really looking at a signal, you aren't seeing the whole picture. Also, these are just signal wire and don't carry any load, so the unloaded ohms test mimics the reality pretty closely.

 

[bezerk]

Re: Distributor 5V Signal - Help

when you swapped out the ECM. did you also swapped the eeproms?

 

[bezerk]

Re: Distributor 5V Signal - Help

atleast i found out with bad ECM''s when you can't connect with datamaster the ecm isn't doing anything

 

[ghettosled]

Re: Distributor 5V Signal - Help

well thats what i figured, but i am not getting 5v anywhere. I'm gonna check the ref wire again at the back of the module.

The other truck i tested the tan wire on, it went 5v for about 2 seconds then back to 0 (with it disconnected, just probing the wire coming out of the ecu). I thought it should have stayed 5v, however as soon as i plugged it in the timing advanced like normal so i was like.... ok Maybe it has to be a closed circuit to stay 5v?.

gonna check voltage and report back.. unfortunately i dont have a scope (dont like working on cars enough to buy one)... just a fluke meter.

thanks

The short answer: The PCM produces the 5V bypass signal that travels to the module over the tan/brown wire

The long answer: The ignition module sends the reference signal to the PCM when the engine starts to crank and of course run. The ignition module receives this RPM information from the pick-up coil in the distributor and sends it to the PCM on the REFERENCE line (ppl/white wire). When the engine speed is under 200-400rpms, the ignition module (ICM) grounds the EST signal (white wire) and controls timing. There is usually still a squarewave (that mimics the reference signal) but is at a very low amplitude (less than half a volt). The ECM sees the low engine speed and does not send a 5V signal to the ignition module.

As soon as it exceeds 200-400 rpm, the ECM will apply the 5V reference to the BYPASS (tan/black wire) line (This line should not "flash". as long as the timing connector is connected and the engine is running over 400 rpm - the line should maintain 5 volts). The ignition control module should then "unground" the EST signal and the PCM will now control ignition timing.The EST wire should then have a nice 5V squarewave displayed. NOTE! IF the vehicle is running it is not likely that the white REFERENCE wire is at fault

TEST: Engine running at idle, check 5V at module. If it's not present check for 5V at PCM. Check voltage at REFERENCE wire. Should see a small voltage, probably 100mV or so.[/U][/B]


Both a open or grounded bypass line or a grounded EST line will cause both a code 42 to be set and prevent the ECM from controlling timing (Advance). I would be using a scope, but a quick ohm check of the two lines with the harness disconnected from PCM and ignition module (to ensure they aren't open) and then with one of the leads attached to a ground (to check for a grounded wire). Of course, so will a funky ignition signal from the stator to the ignition module, a bad module, and a bad ECM. There isn't much else left outside of weird tuning issue. The ohms test isn't the best to use, but outside of really looking at a signal, you aren't seeing the whole picture. Also, these are just signal wire and don't carry any load, so the unloaded ohms test mimics the reality pretty closely.

 

[ghettosled]

Re: Distributor 5V Signal - Help

atleast i found out with bad ECM''s when you can't connect with datamaster the ecm isn't doing anything

yeh i took a complete ecu, chip, etc out of a running truck and plugged it in. nothing. put it back in the other truck and it was fine. So i dont think it is the ecm. I also replaced the coil and the harness from the distributor to the coil fyi with another "known to be working fine" piece.

 

[The_Bronze]

Re: Distributor 5V Signal - Help

The other truck i tested the tan wire on, it went 5v for about 2 seconds then back to 0 (with it disconnected, just probing the wire coming out of the ecu). I thought it should have stayed 5v, however as soon as i plugged it in the timing advanced like normal so i was like.... ok Maybe it has to be a closed circuit to stay 5v?.

I've never experimented (or I don't remember) to see what happens with the BYPASS voltage when the BYPASS is disconnected. It may turn off the 5V completely when it sees: 1) the module pull the EST back to ground (base module timing) and 2) the RPMs are well in the PCM timing range. It is reasonable that it would shut down the PCM control and set code 42. Hope that helps.

 

[bezerk]

Re: Distributor 5V Signal - Help

i might be thinking way offline now, but how does the ECM get's it''s power? from the fuses, and than a relay? or relay than fuses? have you checked if you got any power n the ECM? i''m about 100% sure that the problem is that the ECM doesn''t do anything

 

[The_Bronze]

Re: Distributor 5V Signal - Help

i might be thinking way offline now, but how does the ECM get's it''s power? from the fuses, and than a relay? or relay than fuses? have you checked if you got any power n the ECM? i''m about 100% sure that the problem is that the ECM doesn''t do anything

Worthy things to verify correct operation, but if the vehicle is running, you can still have power and ground issues, but they are there and the PCM (ECM) is doing something.

Ignition from switch to ECM1 fuse to pin BA6 (Switched power)
From fusible link to BB1 and BC16 (Keep alive and main powers)
System grounds at BA12, BD1, GE15 (O2 sensor ground) BC13 and BD7 (Injector grounds)

PCM controls the relays for the wastegate solenoid, CAC pup, A/C clutch and fuel pump.

Something I thought of, even without the check engine light functioning, you could jumper pins A and B of the ALDL and see if the computer "grounds" your testlight (connected to a hot lead and grounded to PIN GE7 of the PCM-Gray/White wire) and flashes codes. That would show that your PCM is able to communicate.

 

[TYTILIDIE]

Re: Distributor 5V Signal - Help

Mike, instead of testing the ECM, have you tried to test the actual harness. The 5v reference(gray wires) are all bundled up in a couple(or one) areas. I would ohm test that circuit with the ECM unplugged. Just test random sensors' gray 5v ref wires. I would also test it at the ECM connector and see if it is going to the cigarette lighter. Somethings may have been hooked up wrong. :2cents:

 

[ghettosled]

Re: Distributor 5V Signal - Help

thanks again for the help guys! I will report back ASAP.

The_Bronze you seem to know alot.. where have you been all these years? And do even have a SYTY, or maybe a syty motor in your samurai ?

 

[The_Bronze]

Re: Distributor 5V Signal - Help

thanks again for the help guys! I will report back ASAP.

The_Bronze you seem to know alot.. where have you been all these years? And do even have a SYTY, or maybe a syty motor in your samurai ?

I haunt enough forums. I had to drop facebook to add this one!

The samurai has a stock 1.3L, but it will be getting a Ford 2.3L Turbo once my other projects get done (or at least further along).

My knowledge base isn't from Syclones, so watch out for my newbie syty blunders. Most of my information is pretty sound though.

 

[Foot Performance]

Re: Distributor 5V Signal - Help

Curious if you figures anything out on this???

 

[ghettosled]

Re: Distributor 5V Signal - Help

nothing yet..

so to me it appears the white (Ref) wire is grounded and shows ~8 ohms with the key off, on and with the truck running. It does not switch open like it should (above 400rpm), and the ECU is not outputing the 5v to the brown/tan wire.

I'm going to have to assume, the ignition module in the distributor is grounded therefore not doing anything once the truck is running.. However that doesnt explain why the same problem with 3 other distributors, one of which is now running in another truck.

I checked all the wires from the ignition module to the ecm and none of them show any ground with the harness uplugged.

 

[The_Bronze]

Re: Distributor 5V Signal - Help

So the white wire is not grounded once you disconnect it from the PCM? Or if you disconnect if from the Dist does it return to 5V?

Do you have 5V at the brown wire with the connector disconnected?

I can't do it today, but my buddy is dropping off his TBI tahoe for me to scope so that I have some waveforms for you to reference. In short, I need to verify that I remember this stuff correctly (although I don't think I could be wrong. )before chasing you down another path. Tomorrow I'll check it out and post back up.

 

[SY-1193]

Re: Distributor 5V Signal - Help

I would like to take a stab at this one...

I would guess you have a custom chip in this truck?
If so is the stock chip attached to the EProm carrier that the custom chip is in?
The reason I ask is the clear covered part of the stock chip carrier you plug into the custom chip's carrier controls the timing and limp home mode.
Did you try plugging in a different one? Maybe it is bad.

>>> Picture <<<

My guess anyway...based on what I read you have done so far..
Good Luck.