'99 Suburban Vortec - Intermittent starting problems -Problem solved!

[Mikey von]

Our only running vehicle is having some issues. We have had it for about 6 months. It has 145000 miles. This has happened only to my wife, so I am relaying the information from her.

The starting issue cropped up on Tues, and it has given my wife problems yesterday and this morning as well. All three times it has done the same thing. It will crank, at a normal speed but not fire up. Tuesday she walked my son to school in the morning after it would not start and then it started right up in the afternoon when she went to pick him up.

Yesterday, It started up going to school, but it would not start up again at the school. Being stranded at my sons school with our other two little ones, she let it rest for about 10 minutes and then it finally fired up (she said she floored the gas while it cranked).

It did not start again this morning. She said it crank over at a normal speed, but would not fire.

The battery shows 12.54 volts in the cold morning (I have been checking it before I go to work) and it started for me both yesterday and today early . Tuesday evening, I checked and cleaned battery cables, including the ground on the block. With the truck running, battery shows 14.3 volts.

Check engine light is not on. We have had issues with the neutral safety switch since we bought it. Sometimes there will be no action in Park, but will start fine in neutral. This happens a few times a week.


I need to get this fixed ASAP. Where do I start?

 

[Fordum]

Well, maybe I can get you started.

Your charging system and battery sound fine.
So, you need to isolate it to either spark or gas.

I know the spark module on some gives problems, but I would not grab one yet.

Next time it fails, turn off all noisemakers, fan, radio, switch the key to on, and see if you can hear the fuel pump come on.
It only runs for a few seconds every time you turn the key on, so you may have to do it more than once.
You might need to stand by the gas fill with the cap off to hear it.

If it runs, switch it off an on a few times, and then see if it will start.
If that fixes it, then you have a leak down problem with the fuel rail. Either the regulator, or a leaking injector.

If that does not do it, then you need to look at the intake and see if any gas is spraying in.
If so, then you need to pull a plug wire and see if you are getting spark.

If not, then you need to check wires around the dizzy, pop the cap and look for problems, and consider the ignition module.

I think there may be a way to test it, odds are someone will chime in with better info.

Of course, Blazer Bash week is a bad time to break down.....

 

[K5dreamer]

definatly agree with the concern about the fuel pump.

the joy of the intermittant problems is that you can really only find it, when the truck isnt starting. so hopefully if your wife is the primary driver, she's also one of those rare and wonderful women that is car savvy .

i know honda's had a problem with the fuel pump relay that caused a situation almost EXACTLY like what youre describing. i know, my sister drove a 1990 accord that did it.

but the above mentioned diagnosis method is solid. when its not starting, see if you have fuel or spark. and backtrack from there. when your wife has been cranking away at it, has she mentioned a heavy fuel smell? and not to be insulting, would she recognize something like that to bring it to your attention? if not, and its possible to switch places as the primary driver, you might want to give that a try. just speaking as a service advisor, alot can be lost in translation. just waisted 2 days trying to diagnose a faulty brake pedal for a customer, only to realize they were talking about the parking brake pedal instead.

 

[Mikey von]

I will go give it a diagnosing this thing a shot here in a few minutes. My wife is pretty sharp, but not super car savvy. No fuel smell she says. I know the fuel pump sound, I will have to ask her if she does and if it makes sound when it is not starting. During the work week, me driving the truck is not an option as she would be stranded and unable to take/pickup my oldest to school, I walk the 1.75 miles each way to my work.

I tried to search the net during lunch today, but did not have much time. I did notice that the V.A.S (anti-theft) sensor seems like a common theme.

 

[Mikey von]

fuel pump

OK, I cannot hear the fuel pump (i was under the tank) and I cannot see any fuel in the intake (will I on a vortec?).

Is there a way to see if the pump is getting 12v without dropping the tank? Dropping the tank seems easy, being only 2 bolts on the straps, but I'd rather drink beer and watch football tonight. If it is the pump, i would like to know tonight so i can order one for Saturday.

 

[K5dreamer]

another point, leave a deadblow or rubber mallet in the truck. if the truck isnt starting, have your wife take the mallet and whack the fuel tank a few times. if its a bad fuel pump the wacking will normally make it start working again. if thats the case, its a matter of replacing the sending unit in the tank.

 

[K5dreamer]

without a wiring diagram im not sure which wires or connections you would want to probe to see if the voltage is getting to and from the pump. Im trying to remember if there is an access panel under the rear seat. im so used to working on my VW's and Audi's, to get access to the fuel tank sending units you lift the rear seat cusions, and there is a pop out panel that is right over the sending unit. it would be alot easier than dropping the tank. especially if its got alot of fuel in it.

 

[Mikey von]

another point, leave a deadblow or rubber mallet in the truck. if the truck isnt starting, have your wife take the mallet and whack the fuel tank a few times. if its a bad fuel pump the wacking will normally make it start working again. if thats the case, its a matter of replacing the sending unit in the tank.

I will give wacking it a try. Sending unit = fuel pump cpu or something related?

 

[K5dreamer]

sending unit = everything inside the fuel tank (pickup screen or filter, electric pump, fuel level sensor, float, and housing).

 

[Mikey von]

anything special about dropping the tank that i need to know?

Thanks for your help! It is much appreciated.

 

[K5dreamer]

dropping the tank is pretty easy, first things first get as much fuel out as possible. some suburbans had 100 gallon tanks... thats alot of weight. id put a floor jack under the middle of the tank, with a wood board to distribute the weight. with the jack holding the weight of the tank, undo the straps, and then slowly lower the tank checking occasionally for any fuel lines or wiring harnesses that are caught on anything or need to be disconnected.

once the tank is down, to get the sending unit out, there is a big lock ring holding it in place. a screwdriver and hammer and use them to tap the lock ring loose. there is also a special tool to release the fuel lines from the sending unit. without it youre likely to bugger them up pretty bad. so i wouldnt try this until you have it. should be able to get it at napa or advance auto parts or something. once the fuel lines are off, and the lock ring is undone, the sending unit lifts out, just be carefull not to catch the fuel level float on anything and bend the arm. then you can remove the fuel pump and install the new one. might as well do the pickup screen while youre at it.

just remember, there are alot of things that could cause the pump to not be running, so replacing the pump right off the bat might not get you covered. it could be a ground, a relay, a power supply issue, etc.

 

[Mikey von]

just remember, there are alot of things that could cause the pump to not be running, so replacing the pump right off the bat might not get you covered. it could be a ground, a relay, a power supply issue, etc.

I was hoping to drop the tank and then check the pump to be sure it is getting 12v. Any easy things to check after that?

 

[K5dreamer]

hhhmmmm...... cant say as its ever easy when its an electrical issue. I would say check fuses but because its an intermittant issue, it could be a bad relay, bad pump, or wire short. If the pump is getting 12v, then you have to check the ground. when youve got the multimeter on the wires, be sure to tug and pull on the wires to make sure they maintain continuity while they move. both for the power and ground. If you are getting power, and the ground is goood, and pump still isnt running, whack the motor with a hammer. if it starts running after that, id be fairly confident that it is a bad fuel pump. If youre loosing power to the pump, my first guess would be the relay. If the ground is coming and going, check the wire for signs of damage or corrosion, as well as the mounting point on the chassis. clean and retorque if needed.

 

[supersize75k5]

Start with the harness on the tank.


I had a 99 vortech burb. The tank is not to bad to drop but you will want a hand with it.


Try the rubber mallet trick.. it does work..well sometimes. If you do get it to start I would still check the fuel pressure.


Start from the front.. check the fuel pressure relay, swap it with another one and check for power at the back. You should be able to find the harness right by the tank, should be 3 wires iirc. One for the 12 v, 1 for ground and one for sending unit/fuel gauge. Find the 12 v and get a voltage reading with your multimeter.

If you have 12 volts.. then you have found your problem. If the mallet trick works I would drive it somewhere that would be more desirable to drop the tank!


Get a fuel pressure tester, pop the hood and look for the shrader "sp" valve on the intake. It should be the bigger one of the two and the valve will be right on top. Fuel pressure should be 58-63 or so. I doubt it but long crank times could be a bad fuel filter or a fuel pressure reg. This will put you on the right path should you be able to hear the fuel pump.. if not: Injectors can also come into play but you need to rule out everything else before throwing money at them!

 

[Mikey von]

So, I ended up dropping the tank to get a hold of the wiring harnesses. I was getting 12v when the key is first switched to on and when cranking (and 5v on one terminal at all times). I went ahead and put a new fuel pump in. Got everything put back together and it seems to run good now. Hopefully this does it and my wife does not get stranded.