Have run many tests like tapping purple wire that goes to module...pump runs, but no injector pulse. Getting 12 volts to inj. and of course fuses, replaced module and pickup coil. I do have some bad injectors though...1.7 on 1 drivers side and a 10.3 on passengers. Tests were done cold. Can't start engine so can't get hot readings. My question is: Has anyone out there had experiance with an injector or 2 causing a no pulse situation like this? How could i know if this is ECM related?

 

if you have spark you should have a reference signal to the ecm. with injectors with that low cold they may have taken out the ecm injector driver. You should contact south bay fuel injectors for a set of bosch 3 22#hr injectors.

 

or check for codes vats will disable injector pulse. but looks like injectors !

 

So, your saying ECM may be blown. Guess new injectors will be good place to start...So, if no pulse when doing tap test, the drivers section could be blown and not rest of ecm? Cuz other parts of ecm seem to be giving readings on scanner

 

No vats codes...and security light does go out...that mean for sure vats is good?

 

same here no injector pulse new injectors new dist no vats code with bypass still no pulse injector OHM's at 14,but getting 4 volts on ground wires

 

you guys know that there is an in line fuse for the injectors right?

 

there are two fuses one for each bank, if you have power 12v koeo on then the ecm injector driver is not grounding them to pulse.

since you replace the icm and if you have spark check continuity on b3 blk/red and b5 ppl/wht of the ecm to the icm these are the dist ref high and low.

any vats codes in the ecm would cut injector pulse as well.

 

good deal on a reman 1227165 ecm the superseded numbers are 16198259 and 16198445.


http://www.ebay.com/itm/AcDelco-1619...#ht_500wt_1078

 

Just a quick note. I think 86 T/A is referring to the ECM/Fuel Pump fuse by the battery. If this fuse were open it would also cause loss of fuel pressure. However, if for any other reason the ECM were not powered up, it would cause this type of symptom. If the ECM is not receiving the fuel enable signal from The VATS module, it would cause this same symptom. Perhaps check the ECM fuse in the fuse panel. Also, while I've seen cases where shorted injector coils took out the injector driver. I've also seen cases where a shorted coil in a single injector pulled up the grounding signal for an entire bank, causing a loss of injector pulse for that bank. A quick test for this is to disconnect the shorted injector and see if the others on that bank have a pulse with the bad coil out of the loop.

 

Hi fellow bird lovers..thanks for responses...got home late tonight, so only a couple tests...yah, fuses are all good but no power at them with ignition in on position? Is that normal? What concerns me more is that there is only 8.20 volts at ecm fuse with ignition on...and lower when cranking of course...think i remember a post saying ecm isn't happy or even working right if below 10.00 volts! Sooo, next i will check wiring and connectors as well as do tests on ecm itself...also will pull battery for load test too...

 

found my problem C7 and D8 wires were crossed in the plug oing to the computer runs now

 

Hopefully, i'll be able to run alot of tests on various parts of car this weekend...if my other baby gives me enough time to..hehe.
A question i have is about the 8.20V reading i got at fuses when ecm conn. are plugged in, yet went back up to normal (11.60v) when unplugged. Is that normal for ecm to cause that much of power drop when hooked up, or is that a sign of problems going on inside it? Seems like alot...

 

If you are getting less voltage plugged up and normal normal unplugged start with grounds then go to pins see if they are in proper location

 

Have run a few tests already and will look at Vats today...is it possible for Vats to allow fuel pump and starter to run, yet not injector pulses?

 

Thats what it is designed to do!

 

Not sure if you understand question...asking if Vats has many parts to it or if it breaks, does everything connected to it stop working or can a part of it fail like ecm? The security light does go out, so it is good, right?

 

Yeah if the light comes on with the key on and then goes out it is working correctly

 

0k, thanks...guess i'll keep checking wiring...think injector circuits may be blown in ecm though..got injectors on the way....guess its off to work for now....later...

 

You can verify the injector drivers are closing the ground side of the injectors, even with just one or even no injectors connected. As I said before, disconnect any injectors that read low resistance, or just disconnect the entire bank. Connect a noid light at one of the disconnected injectors plugs and watch for a flashing light while you crank the engine.

It is possible, and I have seen it more than once, that the VATS module drops the fuel enable pulse. Because the pulse is a non monitored VATS module output, the VATS"security" light will still function normally, as long as the key resistor pellet and circuit check out. It is a 50hz or 80Hz 5v digital pulse(square wave) depending on model year. It is carried by the dark blue wire from the vats module to the ECM. You can test for it with a voltmeter. It will look like about 2.5 volts on a DVOM. Zero or 5v means that there is no pulse. I would use my lab scope and actually see the digital signal.

 

I used the Painless VATS bypass and my voltage is 4 at the pin f10.the injectors will not fire without dist signal also.My harness had pin c7&c8 backward swapped and it runs.Be sure to check pin location.Vats will let it spin and pump run for 2 seconds with key on but it disables while cranking

 

0k, i did get 2.5 volts at ecm pin going to vats. Did test most other voltages there and grounds and seemed fine, so far....have a few more places to test though. Anyone have a direction to next test for next?
Have had trouble finding noid light here, but will try again today to get one. Couldn't i make one too? There is 12 volts at injectors though. Still no injector pulse when tapping purple ignition wire.

 

oem 25143 does your vom read hz so you can test the passkey at pin B6 at the ecm ?

 

The 2.5 volt test result shows me that the VATS module is producing the FE pulse. However, a HZ reading would be further verification. A duty cycle function(should read 50%) would tell us about the same thing.

 

0k guys...meter does have Hz function, just never used it before. It has Hz measurement for volts or current...which one should i use? And not sure what is meant by duty cycle. So touch B6 at ecm and other to ground?

 

Just took Hz reading on pin B6 and it was 28.69 Hz and the bar graph seemed to be pulsing to 50-60% range. What does this reading say then?

 

Some passkey are 30hz and some are 50Hz. Looks like you can now rule out this is not a vats issue.

 

before you toss a ecm at it verify that your ecm grounds are good ecm pins d3, d10 that connect to the rear of the passenger side cylinder head.

 

I will re-check grounds again...what ranges would be acceptable?
What other things should i check besides wires?

 

Can't i just use 12 volt bulb connected to injector connecter and ground to see pulse? Should light go on and off completely, or just dim and get bright as i'm cranking? Thanks by the way for all the help....

 

one bad injector can disable the whole bank, unplug the bad injectors and try to start it then.

 

That was covered post #20

 

0k, ground tests done with ecm connectors off and ignition off...D1-4.5, D3-4.6, D10-4..2, A12-4.5. The power at ecm fuse being 8.20 volts when ecm is plugged in and 11.80 with ecm unplugged seems too odd to me, so i'll get battery tested tomorrow before running down more wires, etc;
What after that though...any suggestions?

 

ECM should definatly have 12 volts going to it with the key on. If not its not going to work properly.

 

I assume these are ohm readings. They are quite high for ground circuits. Shouldn't see more than .5 ohms on any ECM ground. What are you using as aground reference when testing ECM Power? If you are using a body ground, you are including the voltage drop between the Battery and the body in your reading. Check out all grounds between the body and Battery as well as all of the ECM grounds for the cause of the high resistance. A method for testing circuits that I prefer over ohms testing is to test for voltage drop across the circuit while powered and loaded(engine running). Be sure to never use the ohm scale to test ECM circuits with the ECM connected.

 

0k, ran some more wire tests...when i was testing ecm voltage, i was testing at fuse box, and got lower reading when ecm plugged in. (8.20 v. plugged in and 9+ v. unplgged from connector. Anyway...took in 450 CCA battery for testing and he said it was good but didn't have enough amps for my type car...so i put my pickup battery in with 630 CCA and volts came up on all tests 1 volt.
And i do have a bad ground somewhere cuz got 0.5 ohms on the same pins i got 4.5 before....except i clipped clamp to top of intake manifold instead of bolt on chassis firewall like before. Strange thing is, i got 1.4 ohms when clipped to battery terminal. Does this mean a bad fusible link maybe? Wish that ground bolt on head was on front instead of rear though...want to clean and maybe replace ground strap, but sheez, hard one to get to..

 

Sounds like a possible broken fuse link but more like a poor ground connection. It is not uncommon to find the ground points at the rear of the cylinder heads corroded or loose. I know they are a bear to get to but moving them is not advisable, as it may produce RFI noise in the ECM ground circuits and create more trouble.

 

Got a chance to do some tests recently...with ecm fuse pulled out, i get 9.87 v. with both probes on fuse terminals...2.3 v. with 1 probe on fuse terminal and 1 to a chassis ground...and 12.63 v. with probe on other fuse terminal and other at chassis ground...a little strange eh? Any ideas? Also, another update is starter motor drags after a single click is heard...but when going directly from battery positive to purple wire on starter, spins normally...so next i'll check from purple backwards...any simular experiances out there?

 

The starter dragging when the solenoid is activated through the ignition switch and not when activated directly from the battery would point to high resistance in the power supply to the ign switch, in the switch itself, in the park neutral switch, or in the VATS start enable relay. High resistance between BATT- and the engine block to also add to this problem.

One good change that GM made in later years was switching to a start relay and having the circuit through the P/N switch be low current relay primary, rather than handling full starter solenoid current.

 

Tested both pos. and neg. batt. cables to starter and block, and all were about 0.4 ohms. Then tested purple wire coming from starter to what looks like a relay just in front of maf relay on drivers side panel..has a t on side and part # is: 10036951. Got 0.5 on purple wire going to 4 pin connector unplugged, but 6k ohms to the red/white pin. Is this starter relay and is there a preferred way to test it?

 

The start enable relay is under the driver's side kick panel. The preferred method for testing any switch is to test for voltage drop across it, between the large yellow wire and the smaller green/white wire with the relay activated and loaded. You can break the start circuit down into three sections to begin with. First is the power supply to the ign switch which you test for volt drop between the battery and the switch, with the circuit loaded. Then you test across the switch itself, then you test from the switch to the starter. This last section of the circuit includes the start enable relay and the park neutral switch. Through this process, you will find which portion of the circuit is dropping voltage. If you find high voltage drop in the last portion of the circuit, you will then want to test the relay, the park neutral switch, and the wiring between them individually.

Resistance testing an unloaded circuit is of marginal value, especially in high load circuits like starter control. You may find only nominal resistance with the circuit unloaded but when a load is placed on it, it's loaded resistance may go high and pull down voltage. You will only find this through voltage drop testing.

 

Do tests on various switches, relay, and wires require cranking, or just key in run position? I only got 0.5 v. on yellow and green/white wires to relay, even when cranking...also having trouble finding ignition switch on steering...is it that white one with long slender connector? Thanks Doc

 

All voltage drop tests should be performed with the circuit loaded. In the case of the starter circuit, that means with engine cranking. .5v across the start enable relay means the relay is just okay. Much more than .5v drop would point to a bad relay. Did you break the circuit into three parts like I suggested. Better to start there so you can find the portion that is dropping voltage and then break that section down into its components. We try to follow a specific strategy rather than jumping around. This hopefully prevents frustration.

The ignition switch is the one with all the wires to it. The only other switch on the collumn is the dimmer which has only two wires. It is easiest to remove the two bolts that attach the collumn just below the dash and let the collumn hang down to access the switch. Im glad to help anyway I can.

 

0k, i tested the big pos. to starter wire and where red wire comes through bulkhead, and both seemed to ocillate or cycle from 7-9 v. when cranked. What does that say? Never have done a pwr. drop test before, so am not sure of that. I have heard of others isolating area with probes on fuses...would that be meaningful in this case? I'll try to get to ignition and park/neutral switches and associated wiring this evening. It will feel so good to sove this mystery!

 

The volt drop test is simply measuring voltage lost across a circuit. It is basically a measurement of resistance on a loaded circuit. Remember what I told you earlier, that resistance on an unloaded circuit, especially on a high current circuit like the starter circuit, is somewhat useless. Even a mostly severed wire will read low resistance with no current through it. Put a high current load on that same wire and it will drop voltage top the point that the starter will not crank the engine. I have seen too many starters replaced because of broken wires that tested fine with an ohmmeter. That is why we must use the volt drop test to verify circuit integrity. The test is done by placing one probe on one end of the circuit, and the other probe on the other end of the circuit. It doesn't really matter which end is which. We are looking for any reading at all on the voltmeter. The higher the reading, the higher the volt drop. On high current circuits, like the starter motor, you may see as high as .5 volt on one leg(like between the motor and the battery). If you had 7-9 volts at the battery with the engine cranking, you may have a bad battery. It should never go below 11 volts.

 

would it be possible for the starter to take that extra load. say if it was worn/old or the timing was way off and the starter was under a abnormally high load?

 

It is possible for the starter to draw the battery voltage down. You would see abnormally high current on the main battery wire to the starter. The last case I saw of this type was on a 2005 Ford F-150 5.4L where batt voltage was pulling down to 9v and starter current draw was 1000amps(normal draw would be 150-200amps), but that was on an Optima yellow top battery.

The starter in this case was a click but no crank. I did almost replace the battery before I decided to check starter current just to be sure. It was of course a bad starter. Having the starter drive stuck on the flex plate can also cause this kind of symptom. You need an amp clamp to test for this.

 

Update: Happy 4th everyone!
Anyway just wanted say that dragging starter issue was traced to a bad ignition wire that dragged down voltage to starter. Its normal now and so are most other voltage readings...whew! Felt like an endless quest there for a while...anyway, now this thread can go back to being injector related like it began...i seem to have pulse with an led light in disconnected injector conn. when cranking. I have 2 bad injectors unplugged, but still won't fire up any even with starter fluid. There is this smell of combustion in garage though like its trying. Anyone experiance this before? Hope bird will crank after i put in new injectors...if not, guess ecm will be next...also, will that test at ecm referance and ground that gives 2.5v.(is it in HZ.?) verify injector pulse? If there is anything else i can try, let me know...my bird has been in its birdhouse since last winter...hehehe

 

The test for reference pulse only verifies reference pulse. You LED test shows you have something happening at the injectors. I generally use a noid light for thesting injector pulse and if I suspect a bad driver or circuit, I test actual injector pulse waveform with a lab scope. I don't know of any other method. Be sure to verify spark, timing, and no fuel fouled plugs. Not starting with alternative fuel sounds like something more than injector pulse.

I have seen a few cases where clogged exhaust caused an engine not to start. In these cases I have proven the trouble by removing the O2 sensor or disconnecting the exhaust at one manifold. When the engine starts in this state, I am pretty sure that the exhaust is clogged shut. An engine will not start without air movement, either in or out.

 

Could someone please describe in detail how to test the ignition system? Specifically, the key/switch? I don't know a lot about electronics, but I can read simple instructions!

Thanks