Perpetual Diagnostic Black Hole of a vehicle

[Crusty]

Sorry, I must have read over (skipped) that part.

He did mention that there wasn't any fuel pressure bleed down.
With a vacuum leak (repaired), a bad coolant sensor circuit (repaired), no thermostat (repaired), a tossed part, IAC, (the only thing I wouldn't have done), all SIX spark plugs replaced (not just FIVE-!! LOL), the scope trace not picking up the two cylinders warrants a further verification (spark output testing), you are correct to at least LOOK at fuel trims during a road test (which the equipment showing has a very hard time doing 'cause the caster wheels and extension cord have trouble with road tests...LOL)

Not picking at you, just summarizing.

[Witsend]

Hard start Old Tacoed out GM is gonna be the death of me!!!!

Thought for sure with the Counselor cranking amp test on this 6 cylinder showing only 4 cylinders , I was on to something ignition module wise. I pulled the module coil pack And removed and ohmed out coils. All were between 8-8.2K ohms secondary and about a .5 ohm on primary side. Under the bottom of one sooty black and very faint crack on the top middle. Got one new coil , and checked resistance 8.5 k ohms on secondary and .7ohm on primary. Wiped the soot off the old module and reinstalled the 2 old coils with the new coil . Same long crank hard start /no start. Put the new ICM in and it does the same thing but I get it started and idling but missing, idling badly while I scramble hooking up all the counselor DIS adapters, etc and see it's firing on all 6 but not seeing any KV 's much higher or lower between cylinders. I decide to back probe the injector rail connector and discover on fuel injector testing no injector pattern for 3 out of the 6 injectors. Since it was able to idle that long through the testing , figured maybe, just maybe a code set. Nope, still no codes set , LOL. Looks like I got to still do my pin out tests for power and grounds at PCM connectors next.

[Witsend]

Mmmmm module and coil taste mighty good.

Pin out tests of PCM connectors power and grounds checked out good and pass the halogen headlamp bulb load testing. Put everything back together , hook up battery and no crank. No security light on key on bulb check either. checked and Replaced a 10 amp fuse and got the security light to work then go out and crank again. Took about 10 long crank almost starts or 3 cylinder running starts. I get it started and it running fine on all 6 again but at a fast idle . Before condemning the PCM I wanted to test integrity of the Fuel enable circuit blue wire between the theft deterrent module and the PCM but couldn't because the dash/instrument panel removal to access the theft deterrent module makes slamming a re manufactured Rock Auto PCM instead of 2.8 additional hrs of labor to test the blue wire , power and grounds for the theft module. Even though all 6 injectors ohmed out same at 13ohms maybe one is shorting intermittently and drawing higher amperage and PCM is overload protection kicks open the internal path to ground for 3 injector drivers s? The diagnostic scenarios have to reach the end of a tunnel some where.

[Crusty]

Pin out tests of PCM connectors power and grounds checked out good and pass the halogen headlamp bulb load testing. Put everything back together , hook up battery and no crank. No security light on key on bulb check either. checked and Replaced a 10 amp fuse and got the security light to work then go out and crank again. Took about 10 long crank almost starts or 3 cylinder running starts. I get it started and it running fine on all 6 again but at a fast idle . Before condemning the PCM I wanted to test integrity of the Fuel enable circuit blue wire between the theft deterrent module and the PCM but couldn't because the dash/instrument panel removal to access the theft deterrent module makes slamming a re manufactured Rock Auto PCM instead of 2.8 additional hrs of labor to test the blue wire , power and grounds for the theft module. Even though all 6 injectors ohmed out same at 13ohms maybe one is shorting intermittently and drawing higher amperage and PCM is overload protection kicks open the internal path to ground for 3 injector drivers s? The diagnostic scenarios have to reach the end of a tunnel some where.

If the three cylinders not pulsing the injectors are on the same side of the engine, I would be looking at the injector harness to be sure they're all getting proper B+ first.

[Witsend]

If the three cylinders not pulsing the injectors are on the same side of the engine, I would be looking at the injector harness to be sure they're all getting proper B+ first.

When I had it idling on only 3 cylinders and back probed all 6 control side (ground side of the fuel injector harness) the three that were not working showed a trace line at battery voltage with next to no changes, so I know the battery voltage was going to and through the 3 injectors that weren't working.
Even though all the injectors ohmed out at 13ohms, I can't say with certainty that one injector might intermittently draw excessive current spike that internal PCM protection shuts things down. Thinking of taking a current loop and low amp probe both circuit draw spike at key on engine off to compare the initial amperage spikes that occur when I start to crank the engine over.
Still might back probe the blue fuel enable wire at the pcm connector from the theft deterent module to see if there is interruption of voltage signal to the PCM . The car cranks fine , and you would think if it had a theft deterent module or pass key problem, it would not crank either. Don't know if a poor signal to the fuel enable circuit could result in half the fuel injectors working.

[Witsend]

I used a low amp probe and looked at the amperage demands of the injectors while running. They definitely all appear to show a normal draw but I get an amperage spike on all when Snapping the throttle.
With key on and the fuel pump relay disconnected and my DVOM set on 10A scale and put across the fuse terminals, I momentarily grounded each ground side wire of the 6 injectors and they all drew between .8 -.9 amps which seems ok.
Guess if I don't want to pull the dash to access the theft deterrent module to unplug connector and check for a 5 volt signal from the Pcm from the blue fuel enable wire, all I can do is back probe the blue wire at the pcm and check the wire voltage there. If not 5 volts cranking,(the theft deterrent module might be grounding it ,so I might have to cut the wire then re check if I have the 5 volts coming out of the pcm I should see at the unplugged theft deterrent module connector .

[Crusty]

Have you looked at the GM "Cranks-No-Start" or Hard start, A and C charts-??

Read the description and operation for the charts while you go through each testing sequence.

Those charts have always either been bang on, or, they had a tidbit of information that shed some light on the situation. They're not "perfect" but they have always led me in the right direction.

[Joe Rappa]

I used a low amp probe and looked at the amperage demands of the injectors while running. They definitely all appear to show a normal draw but I get an amperage spike on all when Snapping the throttle.
With key on and the fuel pump relay disconnected and my DVOM set on 10A scale and put across the fuse terminals, I momentarily grounded each ground side wire of the 6 injectors and they all drew between .8 -.9 amps which seems ok.
Guess if I don't want to pull the dash to access the theft deterrent module to unplug connector and check for a 5 volt signal from the Pcm from the blue fuel enable wire, all I can do is back probe the blue wire at the pcm and check the wire voltage there. If not 5 volts cranking,(the theft deterrent module might be grounding it ,so I might have to cut the wire then re check if I have the 5 volts coming out of the pcm I should see at the unplugged theft deterrent module connector .

Something is wrong. The first pic doesn't show a peak/hold injector but the second one does. Cars don't switch back and forth. I doubt the problem is with the car though. Try sampling it at a faster sweep speed. think the scope isn't sampling fast enough to see the peaks reliably. They're not consistent in the second pic either.
Joe

[Witsend]

Got to step 8 and the car appears to needs a new ECM, some times she gets all 6 injectors ground switching and will start and run on all 6 , but more often then not it's looses 3 injectors getting ground switched. I could spend 2.8 hrs to pull the dash and do pin out tests of the theft deterrent module connector or suspect the aftermarket Python alarm and remote start system, and put all wiring back to how it originally was, or I can just put a used or re-manufactured pcm in it and hope for the best that is all it is.

[Crusty]

Got to step 8 and the car appears to needs a new ECM, some times she gets all 6 injectors ground switching and will start and run on all 6 , but more often then not it's looses 3 injectors getting ground switched. I could spend 2.8 hrs to pull the dash and do pin out tests of the theft deterrent module connector or suspect the aftermarket Python alarm and remote start system, and put all wiring back to how it originally was, or I can just put a used or re-manufactured pcm in it and hope for the best that is all it is.

Waaaay back in the day......(LOL).... GM would start sequencing the ignition spark plug coils from the CAM sensor (along with the crank sensor), then, initially begin the start up by pulsing the injectors in a "multi-port" fashion (right bank, left bank) until it saw the rpm above 400, then switch to "sequential" injector firing.

ANY time there is some aftermarket system wired in, all bets are off....
Personally, and not being there, I think the ECM isn't pulsing the "multi-port" to start. Who knows why.... Quite possibly an internal fault in the ECM but the aftermarket stuff has sent me around in circles more than once.... (I soon learned to take them out of the system FIRST when there are fundamental problems such as start up)

I`ve seen it where the customer didn`t want the aftermarket crud removed, the ECM got replaced and the original problem is fixed, then a few weeks later, the aftermarket cr ap took out the second ECM.....

HTH

[Witsend]

Sounds like you're really on to something . The tach works just fine One thing left for me to try yet is removing a aftermarket wire spliced to what i think could be the tach wire.Guess you can call it "A plan of A-tach" LOL

[Witsend]

Something is wrong. The first pic doesn't show a peak/hold injector but the second one does. Cars don't switch back and forth. I doubt the problem is with the car though. Try sampling it at a faster sweep speed. think the scope isn't sampling fast enough to see the peaks reliably. They're not consistent in the second pic either.
Joe

I'm sure the time setting could be adjusted better, Though the screen reads "volts" on Lab scope I was actually using the "low amp probe" at the fuel injection power supply fuses 9 and 10 for the fuel injectors to see if one or more of the 3 injectors on each fuse circuit was pulling higher amps than the others . The first picture was amp draw screen frozen at at idle and the second was amp draw frozen on a snap throttle.
Today I cut the aftermarket alarm system wire spliced to the white wire for ignition control that leads to ignition module and it didn't solve starting problem. Next I back probed the PCM connectors The blue fuel enable wire that leads to the theft deterrent module buried behind the dash. At back of pcm connector fuel enable wire did have a pulsed 5 volt square wave at 50 % duty cycle and the counselor showed voltage as 2.5 volts though . Doubt that means it is only going to allow 50% of the injectors to run though.
Next i back probed the 24X reference signal on cranking And I do see 24X signal but a couple of spikes repeating that are lower than the others. After the car starts and runs on all 6 the 24X signal flat lines and it goes to zero volts (like something in the pcm or circuit just shorts it out. KOEO the 24X signal reads steady battery voltage.
I checked the cam sensor wire that also shows the crank sensor wave in it .

I

[Witsend]

94 Camaro cam sensor wire back probed at pcm looks ok below. I don't know why the 24x wire that has battery voltage key on engine off, Displays the 12 v square wave cranking,then after it starts and running on all 6 (KOER) the 24 X signal wire just flat lines at 0 volts.Anyone know if that is normal because I pulled no codes relating to 24x sensor?

[Witsend]

Same long crank hard start, no start with another used pcm

Well i went back to basics cleaned all the grounds, and fusible link connections, found a cracked plastic pcv tube way back behind the engine under the windshield wiper cowl overhang . The broken tube had pulled out of a short piece of oil swollen piece hose that was used to mend the cracked sections together and it fixed the vacuum leak causing IAC code 35.( It must have happened when I was ohming the fuel injectors earlier.
I know earlier I back probed and load tested all the PCM power supplies and grounds earlier at the back of the disconnected PCM connectors with a halogen bulb earlier .
Now I'm really on to something Scratching my head I watched the scanner and the instrument cluster as I very slowly turned the ignition key watching battery volts on the MT2500 and seeing it suddenly go from 12.4 v to zero volts, and scanner actually loose communication between KOEO and the crank position or returning from the crank position to the KOEO position. It sounds like it just starts but releasing the key there is a sweet open spot in the ignition feed long enough the majority of time, that everything needs to go through the pass key security check again before the fuel injectors get enabled again. The passkey circuit was already bypassed , didn't trust it, so I removed resistor and installed my own bypass resistor, but didn't know why the security light still seemed to pop up again cranking, go out and then again returning the key to the key on position then go out again. Be interesting to see if it's the ignition switch or the aftermarket alarm wiring causing the ignition power interruption dead spot between Key on and cranking position to the pcm.

[Crusty]

Could even be BOTH.
Like I said. ANYTHING wired into primary systems that were not part of the original engineering can do funny things, even when they are not broken (yet).

This is a better alarm system than anything wired into the car-!!!

Between the shotgun, the dogs, and the WIFE.....I don't have any worries about anything being broken into or stolen-!!