no spark -- help me figure out why! i have injector pulse, but no RPM signal!

H

henschman

Active Member
Joined
Jul 23, 2004
I have been fighting a no-start condition in my T-Type for some time, and I finally narrowed it down to there being no spark... or at least the spark is so weak that it doesn't arc when the plugs are installed. First, let me say that I have already replaced the ignition module TWICE... it currently has a brand new Borg Warner unit... and it has a known good and tested coil pack on it. I am testing for spark with a timing light, and with the plugs installed, it doesn't light up at all when cranking. I have checked 1, 3, and 5 this way, and none have any spark.

I have gone through the no-start flow chart, and have had some strange results. The noid light test shows that the car IS getting injector pulse, which is supposed to confirm that it is getting a signal from both the crank sensor and the cam sensor. Is this correct? The strange part is that my buddy's OTC scan tool is showing no RPM signal whatsoever when cranking. It just sits at zero. This would seem to indicate that the crank sensor is bad, but would the noid light still flash if this was the case? Is there possibly a backup algorithm for the injectors that would let them pulse even with a bad crank sensor?

Another possibility is that I have my cam sensor installed on the exhaust stroke instead of the compression stroke. Would that cause the RPMs to register zero? they are calculated by both the crank and the cam sensor, right? Somebody help!
 
You could check for continuity in the wires up from the crank sensor, but it sound like that sensor is bad. You HAVE to have crank signal for the spark plugs to fire. The cam signal is needed to correctly time the injector sequence but the injectors will not fire without a crank signal.

To the ECM matter, if there is no crank signal, why should it fire anything!
 
i don't understand why i get injector pulse (and believe me, they are spraying -- it soaks the plugs and there is gas in my crankcase), but i don't have an RPM signal.

Would it cause there to be no RPM signal if the cam sensor was off time? Would it still spark?
 
Just like Scott said, the cam sensor only times the injector firing. If the crank sensor signal is weak or not there, the plug will never light up.
 
but the injectors wouldn't spray without a crank sensor signal, right? they are spraying, and i get a good noid light flash.
 
No, the injectors use the cam sensor to time the spray. The ignition timing (spark) is done by the crank sensor.

The car can run but not start with the cam sensor unplugged (because the ECM will go into batch fire mode) but the car cannot start OR run without the crank sensor, because it times the ignition.
 
are you telling me the no start flow chart here Vortex Turbo Buick Performance is wrong? It says that a blinking injector test light confirms that both the cam and crank sensors are working.

hmm, but on page 2 of the chart, it says to disconnect both cam and crank sensors and jump a wire between leads on the cam sensor, and the injector test light should blink when you crank it. I guess that could only happen if the injectors can work without the crank sensor.

another strange thing is that the car drove normally until i parked it one day, and then suddenly wouldn't start the next. the car wouldn't run at all without the crank sensor, and it seems unlikely to me that something happened to the crank sensor while the car was sitting. Also, a plug will spark a little bit if you take it out of the head and plug it into a wire, but just won't spark once installed. i would think if the crank sensor was bad, it wouldn't spark at all, even with the plug out of the combustion chamber.
 
I would make sure the connection to the crank sensor is nice and clean. I recall mine being pretty oil and cruddy the first time I took a look at it. Also, make sure it is gapped right. If it came loose and the reing the balancer hit it, then it either knocked it out of alignment or probably destroyed it. They are pretty easy to replace. Check the wires for damage as well.
 
ckp/cmp

You are way barking up the wrong tree, buddy. The ckp and cmp sensors are working. Check your powers and grounds at the ignition module. A few volts low at the module can cause pulse/ no spark condition, but, not likely. I've seen it once on a buick and I do driveabiliy for a living. Shoot me a PM if youre still having a problem, will help you diagnose it. Funny, had to have a customer help me diag my washing machine today. We all got to help each other!!!! Dave
 
you're right Dave -- I put a brand new crank sensor on and no change.

you got me thinking, and I checked the motor to chasis ground (the one behind the motor, from the bell housing bolt to the firewall), and come to find out it gets really hot every time the car is cranked! The bell housing bolt is extremely rusty, and probably rounded. I couldn't get it off, so I just got another ground ribbon off a wrecked dodge caravan and ran it from one of the studs for the ignition module bracket to that same spot on the firewall, right over the original ground (which I left in place). Still no spark, and no RPM signal... and the new ground wire still got hot.

I might try to put a heavier ground wire on, and maybe put it in a better place (like from a head to the frame). Oh, and I already cleaned all the mounting spots on the module bracket with a wire brush.

Any other ideas about things to do? If this stuff doesn't work, I'll probably shoot you a PM Dave.
 
did you replace the ignition module and coil because of this problem?

or did this problem start happening after replacing them?

did you do the ignition mod. and coil swap yourself?
 
i replaced the module and coil because of the no start condition, yes.

i did it myself, and yes, i am confident the module wires are hooked to the right places on the coil. i double checked this.
 
If your ground wires are getting hot they are carrying too much current. Have you checked the ground on the front of the engine under the turbo? That one should carry most of the load allowing the grounds on the back to not carry hardly any current. Can you take a multimeter and measure the voltage from the positive terminal on the battery to the ground on the ignition mod with the key on and while cranking? If that strap is carrying too much load it'll act like a resistor and your voltage that's present at the ignition module will be low.

Edit: From the sounds of it you get a spark signal with the plugs not installed, is that correct? If so do you get an rpm signal while cranking with the plugs out? Also, if you do get some spark with the plugs out then there can be no doubt all the inputs are there for spark to happen, so you can forget about the crank/cam sensors.
 
Sounds like it's going to be a weird one. Sorry it wasn't the crank sensor, that would have made it easy. Let us know how it turns out.
 
BlackBandit said:
If your ground wires are getting hot they are carrying too much current. Have you checked the ground on the front of the engine under the turbo? That one should carry most of the load allowing the grounds on the back to not carry hardly any current. Can you take a multimeter and measure the voltage from the positive terminal on the battery to the ground on the ignition mod with the key on and while cranking? If that strap is carrying too much load it'll act like a resistor and your voltage that's present at the ignition module will be low.

Edit: From the sounds of it you get a spark signal with the plugs not installed, is that correct? If so do you get an rpm signal while cranking with the plugs out? Also, if you do get some spark with the plugs out then there can be no doubt all the inputs are there for spark to happen, so you can forget about the crank/cam sensors.
Click to expand...

I don't even see any ground under the turbo on the front. Could somebody tell me where ALL the grounds are supposed to be on this car?
 
The ground he is speaking of actually uses one of the turbo shield mounting bracket bolts. If I remember right, it runs straight off the battery ground.
 
That ground going to the turbo support bracket is actually the negative battery cable,atleast on mine it is.
 
well that might explain why there's too much load going to the rear ground strap... I don't have a ground going to the turbo shield bracket! Either it didn't come with one when I bought the car (which wouldn't surprise me with all the other stupid stuff that was wrong with this thing when I got it), or I took it off when I put on my new turbo. I know I didn't re-install the bottom turbo shield bracket bolt since I couldn't reach it... I wonder if that was the one. Well, I found another ground strap off another minivan... I might put that on. Or maybe I'll make sure its got a good ground and run a battery cable to that bad boy. Thanks for the help guys, I hope this gets it running (and I hope all that ground resistance didn't kill my brand new ignition module)!
 
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