'98 Chevy 1500 5.0L V8 - Turns over but won't start

chevrolet
1500

#1

Alright. I’m a handyman by trade but have only done regular maintenance on my vehicles - I’m no expert. I’ve searched several forums for this information but have found 1000 different answers, mostly for other makes and models. My truck is a 1998 Chevy Cheyenne 1500, 5.0L V8, 137k miles, last tune up at 110k miles. Use valvoline oil explicitly, and change every 4k miles.

I got into my truck this morning, it turned over, and then died. The gauges all activated and displayed adequate oil pressure, battery power, etc. My RPMs got to 1000 for a second and then back to zero. I tried pumping the gas pedal a bit and nothing changed. It will do the same trick over and over with no difference based on time in between.

So I pulled the air filter off and changed the spark plugs and wires. The spark plugs were moderately worn and two had some corrosion. I used the correct gap on my gauge (.06 or .6, don’t remember) and I’ve done spark plug changes a few times in different vehicles. I’m pretty sure it was done correctly. Also, I noticed that the coolant was low, so I filled it up, and added a quart of oil.

No luck. Exact same thing is happening. I really want to avoid electrical issues (don’t we all!) and would like to check other things first… lol.

Please, anything y’all can suggest to help.


#2

i put my money on fuel pump. its fuel or spark. check fuel pressure at rail. could be failed ignition component. do you have spark? use 1 old plug and stick it in plug harness. ground plug. crank motor. do you see spark at plug?


#3

Ok very weird. I pulled the spark plug wire off the 6th cylinder, plugged in an old spark plug for testing, and had my wife crank it over. It sparked, but also the truck started normally. I turned it off, reconnected the wire to the newly installed spark plug, and cranked it back up - no problem.

I assume it was the spark plugs? Or possibly the new spark plugs/wires gave it a stronger start and pushed through a fuel blockage? Pure speculation here…


#4

Also, I added STP fuel cleaner to my 1/2 tank of gas, at the proper ratio, when I added oil and coolant earlier.


#5

Connect a fuel pressure gauge . . . should have 58-60psi key on

And it should hold after you shut the engine off


#6

A number of things could cause a problem like this but the odds of it being due to spark plugs or wires are zero in my opinion.


#7

My first thought was the passlock system. I did a quick search to see if there were any other common problems like this when I ran across this- http://ls1tech.com/forums/pcm-diagnostics-tuning/254638-00-silverado-starts-then-dies-over-over-please-help.html

I was going to post and ask if the problem mysteriously went away when I saw your update :slight_smile:


#8

ok, does the truck key have a resistor chip in it?


#9

Alright. Today, when I went out to start it up, it did the same thing. I pulled the fuel filter off and it is fine, reprimed and attempted, no luck.

I don’t have a fuel pressure gauge to check the pressure on the rail and it’s $60 at Autozone … would rather eliminate other problems then buy a tool I’ll use 2-3 times in my life. Also a fuel pump is $300. My truck is a beater work truck but has always ran great.

Anyway, thanks for the posts about the passlock sensor. I don’t have any resistor chips in my keys, I can guarantee it because they are flat metal keys. I am currently trying this method of repair from one of the links above…

“Its your passlock sensor. Its the housing that your ignition cylinder slides into. Its a common problem on trucks & some GM cars. What happens is the passlock sensor creates a certain voltage reading under 5 volts & the PCM has to learn that voltage or it will start & stall until it does. The passlock sensor voltage reading has changed & you can relearn it to the PCM & you can start the truck again. To relearn, turn the ignition key to the on position for 3 10 minute cycles, turning the key to the off position for 5 seconds after each 10 minute learn. It will start but you may have this problem again & will get tired of having this happen & will need a new passlock sensor eventually.”

About 25k miles ago a box that was in my truck fell over and broke my shift handle, and I had to get my column replaced. I now have 1 key for the door and 1 key for the ignition. I’m not sure if this is relevant.

I’m going to attempt to ‘reset’ the passlock sensor now and let you know.


#10

Okay, it’s not the ‘passlock sensor’. I reset it by leaving it in the on position for slightly over 10 minutes, turning it off for 5 seconds, and repeating 3 times. It still turns over, and dies. It did start the second time for about 1-2 seconds instead of just one turn; maybe two rotations.

This has me thinking it is the fuel pump. My buddy is bringing over a rail tester tonight so we can check it out. I’m going to disconnect the fuel line at the pump and let it run into a bucket while I start it - manual check of fuel pressure.

Any thoughts?


#11

You need to check for spark. Pull the plug and lay it against the frame to ground it. You should see spark when it turns over.


#12

Is the ‘security’ light flashing when it won’t start?

Have you tried jiggling the shifter handle to see if it will start? Perhaps the interlock switch is marginal. The fact you had the column swapped out has me suspecting it’s involved. Just trying the easiest stuff first…


#13

“disconnect fuel line at the pump and let it run into a bucket while I start it”

That is testing the fuel volume

Testing the volume is good, but you still need to test the fuel pressure

You’re on the right track


#14

Does it die as soon as you return the key from “Start” to “On”? If so, you may have lost spark in the “On” position. The ignition system will often boost the spark in “Start” to make it easier to start, then will return the spark to normal levels in “On” to avoid burning the spark plugs and damaging the coil. There could be something wrong with that transition. In older cars this was done by using a low resistance wire in series with the coil primary duing “Start”, then switching (via a solenoid switch) to a higher resistance wire in “Run”. If the higher resistance wire opened, the symptom would be it would start fine, but as soon as you returned the key to “On” it would die.


#15

Well I haven’t got my fuel pressure gauge yet but will try it tomorrow first thing. Never tried the ‘fuel in a bucket’ technique (lol) because I knew the gauge was in route.

The failure is not when I transition from ‘start’ to ‘on’. Even if I turn the key to start and leave it there it dies. I haven’t tried shaking the shifter handle to see if it is seated correctly or possibly faulty. I will try that when I try the fuel pressure gauge.

Also, the security light is not flashing when I am in the start position. I look at my truck warning lights quite often (I dread the check engine light) and have not had any lights on in months and months.

Thanks for all y’all’s help. Great community here - I listened to Car Talk on NPR all the time.


#16

If you’re certain you have good hot spark the next thing to check is fuel pressure. If you’ve still got the original poppet nozzle injectors inside the engine and haven’t updated to the MPFI style injectors then fuel pressure is absolutely critical. You’ll find that the specification for fuel pressure is something like 55-61 psi, but I can tell you that 59.5psi won’t be enough to open the nozzles. You need 60+psi to get the engine started. Once running fuel pressure can drop as low as 40psi without any trouble, but initial fuel pressure is critical to starting.

Let us know what you find.