I have a 2004 Tahoe 5.3L Z Flex that my wife drives. 1 month ago she drove out of a Burger King drive thru and it died. She could not crank it and ran the battery down trying. Had AAA tow it home. I thought it might be alternator but after replacing battery I load tested it and all passed and charging system OK at 14 volts.
Then this week she went to vet. Upon leaving the vet the truck cranked and she pulled out of space and it died. She called me and when I arrived (15minutes) she got it to crank and backed up into space. I rechecked alternator and battery ok, so I followed her home.
I replaced the fuel filter and then check fuel pressure per below:
Key on, engine off = 50 psi
Engine Running = 43 psi
Running and Unplug FPR vent = 50 psi
Engine Turn Off = 43 psi but over 10 minutes slowly drops down to 20 psi.
There are no misfires or codes on engine. The FPR and Injectors were replaced 1 year ago. Does this sound like a fuel pump?
Normally “cranking” refers to using the starter motor. So is the problem that the battery is weak? New cars will stall if battery power gets too low to sustain the computers.
It sounds like the crankshaft position sensor is starting to fail.
When these get hot and fail to produce a signal to the computer, the computer doesn’t think the crankshaft is rotating. The computer then see’s no reason to operate the fuel and ignition systems and the engine doesn’t start.
I was waiting g for that comment. No it’s a separate issue. I don’t have misfires now. This is a new problem just started… I do have a quart of restore in the oil…
You have me thinking about this CAM position sensor. Although I changed the sensor out last October when I rebuilt the Intake manifold gaskets. It could still be a possibility though because what my wife tells me is that when it dies and won’t crank she implies it’s completely dead as though the starter is not turning over. Every time I shoe up it cranks right up. So the starter is good.
I am curious if a bad CPS causes the computer to not engage the starter at all?
I ordered a FP and will drop tank and install this weekend. Should be a fun project. If it keeps happening after that I will go to FPR ($15) and then CPS (Free as I have old one), but CPS is a biatch to get to…
Concur w/above poster, I don’t see anything wrong with the fuel system, given the data you posted.
When an engine cranks but won’t start the first step is to determine if the problem is no spark, or no fuel. Usually it is one or the other. Once you know that the rest of the diagnosis is much easier. The test has to be done when it isn’t starting of course.
Update: btw let me make all know I am a DIY mechanical newby and not a mechanic. But I like doing it and have done a lot.
I rechecked with wife and now understand it has always tried to turn over (not dead). She mistaken the normal starter motor sound verses when starter whirls when disengaged. So ignore that previous comment.
Next the reason I feel confident it’s not plugs, wires, coils, Spark is that I changed all of that out last fall… Last fall it had several codes and 230K miles so I decided to just have fun with it… I replaced plugs, cables, coil packs, wiring harness, intake gaskets, CAM sensor, MAF sensor, MAP sensor, Throttle Body, TPS, FPR, new Injectors, Head gaskets, filters. Did pressure testing and leak down tests. Just now replaced fuel filter… it’s 15 years old and no payments so I am loving learning this stiff.
Ok so if it’s not pump what could it be? The ECU?
It is not the CAM sensor it is the CPS - crankshaft position sensor. Mounted behind the starter on the passengers side of the block at the rear of then engine. You might be able to access it by removing the RH inner splash shield. Makes changing plugs WAY easier, too, if you didn’t figure that out when you replaced the plugs.
After all that work I still had P300 code and rough idle. I was planning on replacing CAM, Lifters and have heads rebuilt. In addition I tried Restore additive to help on compression. Unbelievably it caused my P300 code and EL to clear.
IDEA or Thought… Yesterday I worked on it and noticed the oil pressure at idle was 20psi. My wife said it’s normally on 40 (straight up) because all of her gauges are straight up when normal. Battery, Temp, Oil, etc. I researched and learned that too much oil can froth and cause low pressure. It hit me that the oil a month ago was 5 quarts + 1 quart Restore. Then 3 weeks ago Justin before it started dying I got the idea to drain a quart and add another bottle of Restore. It just hit me that I now in effect have about 4 quarts of oil and 2 quarts of Restore in block. Could this create a low viscosity and low pressure? Would that possibly cause a stall?
Tester oh I forgot that I changed it also. That was a fun project having to pull the starter to get to it… I forgot to list it… The CAM position sensor was on rear top of block. I did that one when I had intake manifold remove… oh I also replaced the knock sensors…
A faulty cam positon sensor usually wouldn’t prevent starting. That part is used to monitor the variable valve timing mechanism, and to let the ECU know whether the next upstroke is compression or exhaust. That’s to prevent firing the spark plugs on the exhaust strokes. When the cam sensor fails it just fires the spark plugs on both exhaust and compression, so it will still start. The only downside is that the double-sparking tends to overheat the coils. A faulty cam sensor usually produces a diagnostic code.
just because a part was installed a year ago, does not mean it is still functioning as it should. This sounds like a crankshaft position sensor to me.
I don’t know the chemical makeup of Restore, but not sure I would run as much in my truck as you are. Currently, 1/3rd of your oil is something other than what the manufacturer recommends.
This is crazy… I changed my oil back to 6 quarts of 5W30 synthetic and oil pressure looks normal!! That’s great but my EL /P300 code returned. That had went away for the entire time Restore was in the oil…3 months… the EL comes and goes and my Torque Pro shows a few misfires only at idle… Approx 2-10 bursting in cylinder 2 and 1-2 on C1&C8.
However it still died on me at a red light… so if it’s not the fuel pump or CPS I am in trouble…
Update 12/15/19 - This weekend I changed the fuel pump. All went well with no issues. It cranked right up. I notice when checking fuel pressure when turning key on /engine off the meter screamed to 52 psi. A lot faster and stronger than old pump… The engine run pressure was a solid 43, only up 1-2 psi compared to old pump. I also notice it idled better at 600 rpm with with old pump it was around 450-500 rpm.
I drove it about 60 miles through various conditions with no issues. During my I ran my Torque Pro app and a pleasant surprise was that I never had 1 misfire in C1-7, with C8 taking a couple misfires on a few occasions for no more than 8 total…
So far this is much better. Time will tell if it solved the stalling no start situation… If it happens again I will look into CPS gap spacing…
I have not read all the previous responses thoroughly enough, Not sure if the Thoe is the same as my TB but in mine the oil pressure gauge is not a real gauge, but an estimate from whatever computer brain. My thought if applicable would be to check the fuel pressure regulator if so equipped. There is a vacuum chose that comes off of it, If it smells like gas it is bad.