'99 Suburban Vortec cranks but wont start

[vdubjunkie]

I've scoured the internet, and others seem to have different problems, or perhaps just with different details to provide. Either way, I'm at a loss.

What I have done:
Determined my fuel pump delivers ~51 psi to the check valve. I can lose about 14 psi after sitting for ~30 minutes.

Engine will run if you spray B12 into the throttle body, so, spark has been tested.

What happened:
My wife had the engine die while driving, but was able to come to a stop and start it right back up. The next time (two days later) after driving around a bit, the same thing happened, only this time twice in a row. She was then able to drive quite a distance home. The next time I went to start it, no joy. It will crank as long as you like. It seems I am not getting fuel into the combustion chamber, but I am getting it to the top of the CSFI body. The GMC service manual for this engine has yet to reveal to me how to test further.

[maxwedge]

You need 60-65 psi at the injectors, so the pump could be bad or you are loosing it under the manifold from the spider/regulator assy.

[vdubjunkie]

This has been the specific debate here. Will that kind of pressure drop actually stop the system from starting? How confident do you feel, because I cannot find anything written to make me feel comfortable with this?

I guess the next step would likely be to pull the pressure regulator out and test it individually prior to dropping the tank to check on maybe a loose pickup tube or failing pump, eh? We did a pump not THAT long ago, maybe three years. (relatively low mileage when compared to the original).

Just trying to make sure I have the next few possible steps figured out!

[maxwedge]

One way or the other the specs call for 65 psi or the poppets will not open.

[vdubjunkie]

Ok, I guess I'll travel that path. Nothing else to do at this time. From what I read, it said the injectors need in the 40s. I dont remember the number specifically, but could look it up. I'll let you all know how it turns out.

Thanks for the prompt replies! Communities like this make the internet a great place!


Edit:
As I think more and discuss with a family mechanic of many years, we think 51psi should at least allow the engine to try, and I get no explosion whatsoever. In this GMC manual, it says the injectors need in the 40s. If there is not a specific thing in the system to tell it not to even try at below a certain psi, then it should at least try, right?

Does anybody know how I can test to ensure that the injector is getting the signal?

[vdubjunkie]

Ok, sorry to be a pain, but I'm really thinking I need to test the injection system from an electrical standpoint, and I've finally found in this GMC 1997 C/K Truck Service Manual the section entitled "Injector Circuit Diagnosis". Unfortunately one of the first things it says to do is use a specific test lamp for these injectors. I'm sure I can just test for voltage or something, but don't know exactly how to do something like that in a definitive way.

[Elbert]

I think you have a fuel pressure problem... Change the fuel filter to start with, its very easy to do..and not expensive. If that does not fix it..then I suspect the fuel pump.

WHile I'm not looking at the shop manual....the manual is clear on the fuel pump test and pressure values. Of course this assumes that the fuel filter is not an issue.

Go change the fuel filter before you start looking at other stuff...

[vdubjunkie]

Well, this has been a nice learning experience. I was assisted in ignoring the slightly low fuel pressure under the idea that it would at least try to start, where all my engine was doing was spinning from a starter motor. However, it seems there must exist a routine in the computer that specifically kills even the attempt to pop the poppets if pressure is slightly outside of range.

I had already replaced the fuel filter because it is cheap and easy to get to, but ultimately I clamped off the return line to discover I was not able to build over 3.7 bar (53.66 psi). One fuel pump later and a tensioner and it's purring again ever so nicely.

Thanks to the community for the support. Hopefully this might help some other would be mechanic out there questioning a similar problem.

[Firehawk97]

I have a 97 Suburban K1500 and I encountered a similar concern. My wife went out and the truck would not start. I put a fuel pressure gauge on and the pressure would build and drop off. Same thing crank and no start, I put a pressure regulator on it and thast solved the problem. Now it starts but its slighlty a hard start, cranks a few seconds and then fires over. My pressure is at 49 so I think the pump is on its way out. GM spec for CFI is 66-60 psi directly from GM Service Information

[vdubjunkie]

I feel certain that my entire problem was a failing fuel pump, and it caused a crank with a "no try" feel to it. By this I mean that I believe no fuel was being delivered whatsoever as I verified spark. The fuel pump replacement isn't bad at all. Take your time and have a seat on the ground next to the tank. Nice thing about a truck so high off the ground. Not at all like my little Subie!

<afterthought>oh yeah, there is that special tool to release the fuel lines that looks like a broken part of a kids toy, but otherwise everything is standard tool box. Also, save yourself the amazing frustration and clean EVERY tiny speck of dirt from under the tabs on the ring in which the pump rests. Do as much as possible before you remove the pump!

[MT-2500]

Originally Posted by vdubjunkie

I feel certain that my entire problem was a failing fuel pump, and it caused a crank with a "no try" feel to it. By this I mean that I believe no fuel was being delivered whatsoever as I verified spark. The fuel pump replacement isn't bad at all. Take your time and have a seat on the ground next to the tank. Nice thing about a truck so high off the ground. Not at all like my little Subie!

<afterthought>oh yeah, there is that special tool to release the fuel lines that looks like a broken part of a kids toy, but otherwise everything is standard tool box. Also, save yourself the amazing frustration and clean EVERY tiny speck of dirt from under the tabs on the ring in which the pump rests. Do as much as possible before you remove the pump!

You need 64-65 lbs of fuel pressure to squirt injectors cold.
You need to run the proper test before throwing a fuel pump at it.

If test show weak pump go with a Delphi fuel pump.
Airtex and aftermarket are junk.


The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.