Help...GM mechanical question

[tbonebusa]

1998 Chevy Tahoe, C1500, 5.7 L.

Two questions: where is the crank sensor located, and what is the function of the 3 wire sensor that is mounted inside the distributor, under the rotor?

I have changed the ignition module located next to the coil, and have 12 volts at the coil, but no spark
while cranking.

Any ideas?

 

[bigjohn141]

The crank sensor is located on the front of the block on the passenger side kinda under where the lower radiator hose goes into the pump, it is a lot easier to see from under the vehical. The sensor inside the distibutor is the cam position sensor. Have you had the distributor out lately and are you getting any engine codes?

 

[tbonebusa]

No, distrubutor has not been pulled. Just completely lost all ignition a couple days back. A long distance friend advised me that this year was notorious for eating ignition modules and crank sensors, so I picked one and replaced it ( the ignition module). No change. So I guess the crank sensor is the next part I throw at it, eh?

 

[bigjohn141]

You can try the crank sensor next but if have access to a obd 2 scan tool it would be best to get the trouble codes from the computer to track down the problem. It could turn out to be cheaper in the long run rather than replacing expensive sensor that dont need to be replaced, If not go for the crank sensor. I dont remember if it is the same for the crank sensor but I know if the cam sensor goes out the computer will actually produce a sort of fake signal to "limp" the vehical to a service center insted of just leaving you stranded. Good luck to ya

 

[unkleslapnutz]

You have power to the coil but no spark..What about the coil? The whole ignition system around that time on the 5.7 was kinda iffy. The f-bodied cars were known to have issues all the time.

 

[tbonebusa]

Put a scan tool on it last night...no codes. Any clues? Should i just go ahead with the crank sensor?

 

[tbonebusa]

bump....c'mon, i know there are some smart chevy guys out there....

 

[heavybusa]

a.k.a. Bump

 

[bmbusa]

Try to tap on the crank sensor while someone else is cranking the engine, sometimes this will cause vehicle to start, then you'll have to replace it. If that doesn't help, check for pulse at the coil neg. terminal. If there is no pulse, then you need to check the digital wave signal from crank sensor,should be on then off, a square wave signal. If that is ok, it's probably a ECM problem. Oh yeah, you can use a test light at the coil neg. terminal, ground the test light and probe the terminal, should flash when cranking.

Good luck.

 

[extreemachine]

WHAT??

 

[tbonebusa]

(bmbusa @ Nov. 29 2006,19) Try to tap on the crank sensor while someone else is cranking the engine, sometimes this will cause vehicle to start, then you'll have to replace it. If that doesn't help, check for pulse at the coil neg. terminal. If there is no pulse, then you need to check the digital wave signal from crank sensor,should be on then off, a square wave signal. If that is ok, it's probably a ECM problem. Oh yeah, you can use a test light at the coil neg. terminal, ground the test light and probe the terminal, should flash when cranking.

                                                                        Good luck.

That gives me some specifics to look for...many, many thanks. I'll try it tonight.

 

[bmbusa]

(tbonebusa @ Nov. 30 2006,12:00)

(bmbusa @ Nov. 29 2006,19

) Try to tap on the crank sensor while someone else is cranking the engine, sometimes this will cause vehicle to start, then you'll have to replace it. If that doesn't help, check for pulse at the coil neg. terminal. If there is no pulse, then you need to check the digital wave signal from crank sensor,should be on then off, a square wave signal. If that is ok, it's probably a ECM problem. Oh yeah, you can use a test light at the coil neg. terminal, ground the test light and probe the terminal, should flash when cranking.

                                                                        Good luck.

That gives me some specifics to look for...many, many thanks. I'll try it tonight.  

You probably don't have access to an oscilloscope to check crank sensor and cam sensor, but you might know somebody that does. When you check the pulse at the coil, if it is present, then you know it has to be a coil. You might want to check for injector pulse also with a test light.