2001 Suburban 5.3L Cranks but no start, Solved

[crpdm]

I am at my wit's end. Two months ago, the truck started dying randomly while driving. Hot, cold, full tank, empty tank, fast, slow, did not matter. Usually it would start right up again and be fine for a week or so. Two weeks ago, it died, but would only run for a minute or two before dying again. I let it sit overnight and it was fine. It seemed like it was an intermittent fuel problem, so I put in a new fuel pump. I saw that the pump had been previously replaced and the connector was spliced in with crimp connectors. I replaced these with solder/heat shrink tubing thinking this was probably the source of the intermittent problem. It ran fine for a week, then last Friday it died on the road but would not re-start. It will fire up for about 1 second but immediately die. There was a P0335 "Crankshaft Position Sensor a" code, so I replaced the crankshaft sensor with a $12 amazon special. This made the problem worse, as it would no longer try to start and would crank very unevenly, as if the timing were way off. I was till throwing the P0355 so I replaced that sensor with a $70 AutoZone sensor and now it is back to the one second starting scenario, but no more code.

•  
• There is no visible damage to the connector or wiring for the sensor.
• The fuel pressure is 55-60 psi and does not drop when it momentarily starts.
• I read on this forum that the engine would not spark at all if the sensor was bad, so the momentary starting points away from a crank sensor problem.
• The fuel pressure regulator appears OK (no leak from the vacuum tube)

I have seen a few postings on the web regarding a bad ground wire at the rear of the engine that could cause this problem. The ground wire appears intact and well connected. Can anyone advise where this ground wire goes after it disappears into the harness? Then I could test with a jumper without cutting into the harness. 

 

I would greatly appreciate any suggestions as to what next to try.

 

Thanks in advance,
Karl

 

[riverbanks]

It's usually the braided strap that causes issues,how did the wires look at the crimp connection?I would pull the fuel pump relay out and check that connection and check ground for pump at box mount near fuel filler neck

[crpdm]

Thanks for your input George,  The braided strap from the firewall to the top of the engine looks fine.  and feels secure at both ends.  At one point, I did try using a jumper cable from the firewall anchor to the engine as a test, but there was no effect.  There is a second single 14 gauge wire that runs from the same point on the bell housing into the harness at the rear passenger side of the engine.  This also appears fine, but I don't know where it goes.  There is a remnant of another ground strap on the firewall to the left of the first one but the strap is missing.  I think it went to the hood?  It has been missing since I bought the vehicle in 2011. 

 

The crimped butt connections at the fuel pump connector looked OK, but I cut them out just-in-case, cut the harness back to clean wire and soldered in the new connector that came with the new pump.  I did check the fuel pump relay but I think it's fine.  I can hear the pump whirr for a few seconds when the key is turned on and the pressure  jumps up to 55 psi. It bounces between 55 and 60 when it momentarily starts, so I have not been focusing on the pump.  I will look at the ground though tomorrow morning.

Thanks Again,

Karl

[riverbanks]

That ground is for a few sensors,oil level,MAF,iat,and a few more, speaking of MAF,unplug it and try it,it is one way they fail

[mjm-1957]

Is the security light on? Scan for trouble codes and see if you have P1626.Sounds like it may be in fuel cutoff from a theft deterrent issue.I dont know how to cut and paste anything but have two DOC ID's that may be of help-1873859 and 722216. You can also monitor the fuel enable command in engine data and see if the PCM is allowing the fuel pump to run or turning it off due to a theft deterrent problem.

[Black02Silverado]

I know it doesn't have anything to do with it but has the fuel filter been changed?  Maybe something inside it will clog when ran and then settle down when fuel supply is off. 

[crpdm]

Thank you all for the suggestions. 

• I tried dribbling fuel into the intake.  This let it rev a little higher during the momentary start, but did not let it run any longer. 
• Unplugging the MAF had no effect. 
• I checked the ground continuity on the MAF and determined that the ground wire is OK. 
• The theft deterrent system seems to be working normally.  The "security" message goes away when the key is inserted and does not come back or flash after the stall. 
• I have only a cheap scanner that can read and reset OBDII codes.  I am unable to monitor the PCM data.
• As of now, there are no codes.

It does seem as though the PCM is shutting down the engine after 1 second, but I am at a loss why.

[riverbanks]

So back to crank sensor?,on, troubleshoot my vehicle.com/how to test a crank sensor might be of help,or check harness from it all the way to behind power steering pump,a rub spot,if you had scanner,you could watch rpm's while crank and run(short run)to see if signal is lost

[crpdm]

Yes,  I think that I will need to access the sensor input at the PCM to verify the signal is getting through.  I haven't figured out how to get the cover off the PCM yet.  Thanks to everyone for the help and Happy Thanksgiving to you and yours.

 

PS.  The fuel filter is 2 years old and fuel pressure is good,  so I have put that way down the list.

[crpdm]

So the problem has been solved, and like many such mysteries, the problem was self inflicted. During my time troubleshooting the fuel pump, I was having a problem with the battery going dead. I found a high leakage current from a fuse in the electrical center and pulled it out. The Fuse is labeled RAP#2 in the owners manual (for Rear Power Windows, Sunroof, Radio, Onstar). I put in a new battery and reinstalled the fuse and now it starts right up. D'oh! I think the original problem was caused by the bad crimp connections on the fuel pump and the rest was just me getting in my own way. Thanks again for all of your help.
Karl

[davester]

thanks for posting what your fix turned out to be