weird random crank/no fire issue

[SteveCZ28]

i have a very weird, but random crank, no fire issue. this is the 3rd time in about 6 months its happened. I get into my 05 Tahoe, turn key, and itll crank and crank and crank but no fire. I have fuel pressure, and can hear pump running. I checked all ignition related fuses and their all good. I happened to check the ignition relay. there are only 3 relays this size. 1 is for parking lamps, the other is starter, and the 3rd is ignition2 or something similar. I swapped the parking lamps relay with ignition relay, and as soon as it made contact, you could hear the relay click, then the truck would start. this happened again yesterday morning as I tried to leave work. only this time I swapped all relays, and couldn't get it to click to start. I randomly left the key in on position, removed the relay, and swapped it with another of the 2 I had, and it clicked right away and then the truck would start after I cycled key to off, then back on and start. its very weird, and hate that its so random. I hate that potential punch in the stomach feeling that you might be stranded somewhere and would need to find a way to get me, and the truck home incase it just doesn't do the trick this time around.
any ideas? I don't know if its a weak relay or not, as I can swap it with one of the other 2, and they all continue to work.

 

[retiredsparky]

After reading twice, it seems that any of your relays in the ignition relay location will fail to fire intermittently. For this reason, I don't think it is a relay problem. Relays are a lot like guys--very simple. Either they work, or they don't.

Without a wiring diagram I will guess that it could be the security system, ignition switch or PCM problem or a corroded ground connection.

The relay is probably ultimately controlled by the PCM either through a tiny pc board mounted 1 amp relay or more likely through a power transistor. The circuit also probably runs from the PCM through the security system before arriving at the ignition relay.

If the ground connection for the relay or the coil packs is corroded, intermittent running could happen, but you would have that same problem while going down the road.

I would change out the ignition switch first to eliminate a dirty contact. The ignition switch provides ignition power both in run and in start position. With no diagrams and detailed wire harness knowledge, it is a crapshoot!

Larry

 

[SteveCZ28]

ok this same issue happened to me again yesterday after work. I switched relays back and forth maybe 6 times with no luck. I noticed the passlock light was flashing really fast this time when the key was in on position and not cranking. a guy was ready to give me a ride home, so I slammed the hood shut, and tried it one last time, and it fired up like nothing happened. and the paslock light stayed off this time.
im thinking of replacing the ignition switch now, and do a reprogram. hopefully that eliminates this issue. any other ideas?

 

[ccapehartusarmyINF.(ret)]

check and make sure all yer grounds make sure all the terminals are all tight
i had pretty much the exact same problem with my tahoe the negative batt terminal got a little lose and randomly it wouldnt start just click then i turned it over again it fired
and then in my suburban the same terminal got a little lose and cuased it to start and the engine would die immediatly id go tighten it and bam runs good

 

[SteveCZ28]

grounds look ok, and the terminals are tight on battery. I have the big 3 done, and all the additional terminals are tight as well. once the truck actually starts it runs perfect with no issues. its just getting it to start sometimes.

 

[ccapehartusarmyINF.(ret)]

View media item 21768dude check those terminals again the terminal on my battery was just loose enough to were i could twist it with some effort it seriously dumbfounded me how just a little bit loose could cause a no start or better yet check all the grounds with a volt meter for high resistance cuz it just so happens i also did a big 3 actually its a big 4 upgrade before had this issue

 

[ccapehartusarmyINF.(ret)]

you can see some of my big 4 upgrade
the wire from back of the alternator to the orange box gets changed to zero guage the ground from the bumper to the batter, engine block to the battery and the ground that connects to the back of the engine compartment replace that and hook it to the battery vviola 4

 

[SteveCZ28]

I have battery negative to frame( front left bumper support) then battery negative to engine ground (ground stud on front of alternator mount) then battery positive to alternator output stud.
all of these connections are all tight and clean. I even applied a good amount of force expecting any of them to turn or spin, with no luck. so I know theyre tight.
when this no start issue happens, motor turns over fast like normal(actually it turns over like normal for about 5 seconds, then its like it goes into boost mode, and spins what seems like twice as fast until I let go of key). just no fire (my guess is no spark) as I have fuel pressure everytime.

 

[retiredsparky]

A couple of parts to suspect: Ignition switch has multiple contacts. If the contact that sends power to the ignition system fails, then no fire to plugs. A second suspect part is the cam position sensor. If it fails, no spark to plugs.

It is not possible for all the coil packs to fail at the same time. If the security system were the cause, the starter would not spin the engine.

Since you apparently do not have the tools or electrical drawings you will have to either start replacing the above mentioned parts or take it to a mechanic.

 

[SteveCZ28]

im having problems finding the whole ignition switch. I can find the ignition lock tumbler and a new key, or the housing that bolts to the column. none of these appear to have electrical connections though. which is confusing to me.