Troubleshooting

Stealthfxxr

New Member
Joined
May 25, 2001
Ok guys i'm trying to troubleshoot my 85 been sitting for a week and now wont start. Check ECM and CCI fuses both good, got fuel but no spark. What should i check for in the ignition system?
Dale
 
crank and cam sensor would be first to check.

both can be checked by probing the middle of the three wires going to them and with the key on turn the motor over manually with a ratchet short ext. and 1 1/8 inch socket on the crank bolt.

if the voltage goes high to low and back to high as the motor turns then they are ok if no voltage change you got a problem

you wont have t turn the motor to far to see the change on the crank sensor put the cam sensor only puts out signal every two rotations of the crank so you may have to do alil twisting for that one
 
Red, did the test on the cam sensor and the voltage went from 10.7 to 7.9 and back to 10.7 so i'm assuming its good. The crank sensor showed 7.1 and when i tuned it varied from about 5.5 to 7.1. The voltage change on the crank sensor doesnt seem to be consistant either. Is there any way i can hook up a 86/87 sensor to try out? Got a new around hear somewhere.
Dale
 
you can just plug the sensor into the harness but it wont reach the crank so just probe it and side a piece of metal in the slot fartest away from the plug and see your voltage change

if it shows a big difference from the original then there ya go .

i did one that was bad and used an 86-87 one but i had a plug with wires so i just spliced the two together.
 
Here's a test procedure I posted about a week ago...it's lengthy, but if all else fails, it may be worth your time! By the way, this is all taken from a GM troubleshooting flowchart that I just tried to translate here! I want to try & get a good scan of this flowchart and put in on the internet! Until then, here goes!
(PS, if you're using internet explorer6, and you have that 'fit image to page' thing on, note that these pics are BIGGER than the page!)

Below are links to repair manual pictures to reference from:

ECM Plug
Sensor Plug

You'll need to get at the ECM and the cam & crank sensors to do some voltage tests. If you have a NEEDLE type voltmeter, it may work better for these tests, as it will visibly "swing" when the sensor switches open & close (IF they're working okay!)

Here goes:

First, test your meter and ground! (see ECM Plug) Check connection A-6, "ign, ECM fuse" for 12 volts. (for ALL tests, BE SURE the negative lead of the voltmeter is connected to a GOOD GROUND!)

#1- (see ECM Plug) With the key off, disconnect the ECM A-B connector. With the positive lead of the voltmeter, probe the B-5 connection (highlighted yellow, this is the crank sensor signal) Crank the engine and watch the meter...you should have varying voltage from 1 to 7 volts.
If NOT okay, proceed to #2.
If you ARE seeing correct voltage, your cam & crank sensors are okay, and your coil and/or ignition module may be the problem! You need to loosen the coilpack, and check the BLUE wire for 12 volts, key on. If it DOES have 12 volts, then the problem is likely the ignition module.

#2- now probe the A-11 connection... (highlighted green, this is the cam sensor signal). Crank the engine...you should have varying voltage from 1 to 9 volts.
If it IS okay, THE CAM SENSOR IS FINE, AND YOU ONLY NEED TO TEST THE CRANK SENSOR IN ALL FURTHER TESTS!
If it's NOT okay, there's no cam sensor signal!

Plug the ECM connector back in, and head for the sensors!

#3 (see "Sensor Plug") Unplug the cam sensor plug. Turn the key "ON" ...On the MODULE SIDE of the plug, probe the "A" wire for voltage, after which probe the "B" wire for voltage. You should have between 5 and 11 volts on BOTH wires.
If you ARE seeing correct voltage, THEN: with the negative lead of the voltmeter, probe the "C" wire, and with the positive lead probe the "A" wire. You should have between 5 and 11 volts. Note the results, then REPEAT THIS TEST WITH THE CRANK SENSOR PLUG!

If ANY of the sensor plug tests FAILED, you have a probably ignition module problem...
If ALL the sensor plug tests PASSED, then PLUG IN the sensor plugs, and proceed:

#4. Test the cam sensor: Probe the "B" wire of the cam sensor, then crank the engine and watch the meter. You SHOULD have varying voltage between 1/2 and 9 volts. REPEAT THIS TEST WITH THE CRANK SENSOR!

If either sensor fails this test, then it's possible that sensor is bad! If they PASS this test, it's likely the ignition module, or the connections TO the ignition module are bad)

Hope this makes sense!
 
Kevin thanks for the info i saw the test you posted before and printed it. Gonna do them tommorrow ran out of daylight, i'll let you guys know results.
Dale
 
Dale, I just copy/pasted this from the prior post--I shoulda mentioned that I was a bit concerned about your voltage readings on the cam sensor, the low voltage should be nearly zero.
 
Thanks Kevin, i'll check it again to be sure but those are the numbers i was gettin when i tried before. May have to go to work and get an analog meter and try it again.
Dale
 
Take your black and red prob from your meter and check your settings touch them togeter and your meter should beep , try this setting .

Pull the plug apart to the cam sensor and go from the black wire from the cap to the blue wire . Check all three wires if your meter starts beeping when the red prob is on the blue wire and the black prob is on the black wire then your cap is bad , you will have a short from grond to the sensor wire.

Just prob all three wires and see what happens this is how i found my bad cap, it sounds a little crazy i dont write very good:D

hope this helps
 
Crazy, i went out and probed from the middle green wire to the black wire and it was open, same from green wire to red wire. From the red to the black i got 3Megohms. Will this test work for cam sensor also?
 
Iam not sure about the crank sensor you can test it and see what happens and then test the 87 crank sensor they should be the same i would think.

When i did my cam sensor i pull the cap and tested the wires ,when i got any thing though the wires i new it was bad . My cap was shorted at the black and blue wires you should get nothing when you check this .

i am going to check my meter if its here and see what the setting is .
 
Ok the setting on my meter is ohms it looks like a upside down house shoe. Or test the settings on the meter when you touch them togeter they should make the meter jump or make a sound, the probs that is . Now if you have this on the right setting and your meter jumps or beeps then you have a short in the cam sensor , blue to black you should get nothing. And if you do have two crank sensors there do the same check both if there not the same when you test it some things wrong.


Let me know how it go's
 
Ok guys started doin the voltage test that Kevin posted and here's what i got so far;

#1 got 4-5 volts then 10.77 on blue wire

#2 got 7-9 volts and saw 5 volts once

#3 for the cam sensor got 10.4 - 7.01 - 10.4
for the crank sensor got 11.34 - 10.77 - 5.5

The batter seens to be getting low so i'll charge it before i do test #4 the numbers i got from doing this test yesterday were
cam 10.7 - 7.9 - 10.7
crank varied from 5-7
thanks for the hel p guys.
Dale
 
#2 got 7-9 volts and saw 5 volts once

Dale, I think you may have located your problem, if the cam sensor isn't getting below 7 volts (or 5 even), I don't think it'll trigger the ECM...(it also means the switch isn't closing!)

To be sure, you need to test the cam sensor without cranking it! (it may be your voltmeter is reacting too slow) Line up the timing mark to TDC, but BE SURE the #1 cylinder is on the COMPRESSION stroke! (one person turning the crank with a ratchet while another feels for pressure at the spark plug hole works for me!)

Now, the BEST thing to do is follow the cam sensor setting instructions in this link: Click Here!

Now, besides setting the sensor, what I'M concerned with is that you're getting the proper voltages!

If you're NOT getting the proper voltage readings, pull the cam sensor cap, and make sure the pickup in the cap and the slot in the rotating ring are fairly close to being lined up like they should be!

Let us know what you find!
 
Thanks for the info Matt, i'm getting wierd reading from both sensors, yesteday i got 10 and 7.9 on the cam and today i got a varing 4-7 on the crank got 5-7 yesterday and today got 6.5. Gonna try a different meter tommorow goi to would and pick up one. Sorry didnt give you a call last week with this war going on i'm workin different hours. I may try to make it this weekend if your not busy, i'll call and let you know.
Dale
 
Did the cam sensor set proceedure and volts only went down to 5.4vdc . Does this equal a bad sensor?
Dale
 
Do you still have fuel? Is the coil/module grounded? Are the grounds by the AC good?

Dale, I didn't realize it was you. I didn't know your TB username. I'll be around this weekend, just let me know when. You wouldn't happen to own a digital camera, would you?
 
Dale, if it's not going down to near zero, then I would presume somethings wrong with it, because near-zero voltage indicates the switch is "closed", and if a switch don't close, it ain't much good!

And Matt, I think Dale means he's getting fuel at the rail (yes, no Dale?) :confused:
 
Yes guys i meant that i was getting fuel at the rail I guess i need to get anothe cam sensor from the readings i got. Matt the grounds are all good, I checked them first thing this morning. I do Have a digital camera and if your not busy will shoot up that way on sat. (the way i drive can get there in little over and hour). I hvae a question is'nt the crank sensor the same type switch? Should it go to zero also?
Dale
 
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