Need help… Crank/no start + Really bad MPG

[Rayyy]

2004 Vortec 5.3 4x4

It never, ever starts on first try. Cranks, but no start. However, starts right up on the second attempt every time.

Also, truck seems slightly sluggish. It still pulls at WOT, just seemingly not at 100% power.

MPG is a wopping 8.1MPG (confirmed by calculating manually using an MPG app too)… Even when I cruise around in town below 2,000rpm for the entire tank.

@ idle RPM
STFT 2.3+/-
LTFT +4.7 (bank 1) +6.2(bank 2)

@2500 RPM
STFT -4.7
LTFT +7.8 (both banks)


So far, I’ve replaced the plugs, wires, valve covers, intake air filter, MAF, brakes.

I’ll be adding some additives to the next tank to try to clean the fuel system and injectors, as well as replace the fuel filter.

Wondering if anyone has any idea of what else it could be?

 

[Doubeleive]

I would replace the fuel filter and see what the fuel pressure looks like both key-on engine off, and engine running.

 

[Fless]

I would replace the fuel filter and see what the fuel pressure looks like both key-on engine off, and engine running.

^^^ This. Test fuel pressure at the fuel rail. Use the standard KOEO test, as well as when it's running.

Based on your RPO codes you have a non-Flex Fuel LM7 engine.

 

[RAMurphy]

As already been stated. Get a good reading on your fuel pressures and replace that fuel filter. Have you tried to turn the ignition to "on" for a 3-5 seconds (to build up fuel pressure) before cranking to see if that helps your first start. Before replacing my original fuel pump (290K miles), I was having a similar problem during initial start.

 

[OR VietVet]

My girl's 2002 TrailBlazer is going thru that initial crank and no start or long crank before start. 3-5 seconds KOEO and then starts as normal. The problem is very intermittent. Lots of power. I have ran tests and know it is the bleed off of fuel pressure at the pump. Great pressure but bleeds down to about 30 psi in an hour and bleeds more the longer it sets.

 

[OR VietVet]

By the way, I did not just assume the pump was the bleed off. I checked by pinching the fuel return line. I saw very slight clean area at fuel pressure regulator, like a fuel leak, and I replaced with a Genuine GM part.

 

[Rayyy]

By the way, I did not just assume the pump was the bleed off. I checked by pinching the fuel return line. I saw very slight clean area at fuel pressure regulator, like a fuel leak, and I replaced with a Genuine GM part.

What did you replace? The fuel pump?

 

[Rayyy]

My girl's 2002 TrailBlazer is going thru that initial crank and no start or long crank before start. 3-5 seconds KOEO and then starts as normal. The problem is very intermittent. Lots of power. I have ran tests and know it is the bleed off of fuel pressure at the pump. Great pressure but bleeds down to about 30 psi in an hour and bleeds more the longer it sets.

How is the MPG?

I don’t believe the 02 had the Average MPG in the cluster… but, there is an app called Fuely, which calculates for you and just requires to input odometer/fuel at each fill up.

 

[OR VietVet]

What did you replace? The fuel pump?

No, so far, only the fuel pressure regulator and I had done the fuel filter because the vehicle was new to us and I always do that. At that time, we knew of no start problem like I described.

 

[OR VietVet]

How is the MPG?

I don’t believe the 02 had the Average MPG in the cluster… but, there is an app called Fuely, which calculates for you and just requires to input odometer/fuel at each fill up.

Not really worried about MPG. It is her around town vehicle, so she has a smaller vehicle to park easier and still carry loads in back. I have my 05 Z71 and she has a 1990 Chevy K2500 ext cab truck with a shell on it. Only has 128k miles on that truck and is as solid a rig as there is out there.

 

[Rayyy]

Not really worried about MPG. It is her around town vehicle, so she has a smaller vehicle to park easier and still carry loads in back. I have my 05 Z71 and she has a 1990 Chevy K2500 ext cab truck with a shell on it. Only has 128k miles on that truck and is as solid a rig as there is out there.

Ah okay, so if your Trailblazer was operating at 50% efficiency of MPG (like mine is), that wouldn’t concern you?

The leaky fuel pressure regulator fixed the no start issue?

I’m wondering because low fuel pressure could very well impact the MPG, no?

 

[OR VietVet]

Ah okay, so if your Trailblazer was operating at 50% efficiency of MPG (like mine is), that wouldn’t concern you?

The leaky fuel pressure regulator fixed the no start issue?

I’m wondering because low fuel pressure could very well impact the MPG, no?

I had 2 problems. One was the long crank before start, intermittently. If turned KOEO and waited 3-5 seconds, there is no long crank before start. I did replace the fuel pressure regulator for that because I could see a very slight "clean spot" on the regulator body where it looked like fuel was leaking out and cleaning that area. I did a couple other tests for the problem that I stated earlier and decided that the fuel pump is losing the pressure. The pressure never drops below 15 psi when I had a gauge on it for 4 hours. I am convinced it will need the pump. The mpg has not been checked because it has never been out for a "trip", per say. It is strictly around town as a run around items gatherer and used because of the convenient rear hatch.

The other problem was that during an engine crank to start, the cranking would just stop-like the battery was dead but it is not. I have checked for connections, corrosion, voltage drop and all tests good and this problem is very very intermittent. I am convinced that the problem, well known problem for these rigs, is the ignition switch. I knew about this problem when I bought it and when I went looking for a new switch replacement, the only thing available was the aftermarket Dorman or Standard Parts switches and I installed the SP switch and all was fine until recently. Mind you, the intermittent problem I have now was never experienced with the original switch that I swapped out and I actually still have. I did finally find an AC Delco D1426D switch and should have it in my hands by the 29th. It is literally a 15 minute labor time install.

If either of these problems would just fail completely, I could diagnose and know exactly what is wrong. I will get there for sure. I will not give up.

 

[rockola1971]

Assuming no codes are being thrown, the stereotypical doesnt start until the 2nd or 3rd crank on a fuel injected engine is typically leaking fuel injectors flooding the engine or a fuel pump is dying. Ive had a fuel pump do this for over 6 months until one day it finally decided to just die....while I was cruising down the highway 60mph and 45mins from home.

 

[Rayyy]

Assuming no codes are being thrown, the stereotypical doesnt start until the 2nd or 3rd crank on a fuel injected engine is typically leaking fuel injectors flooding the engine or a fuel pump is dying. Ive had a fuel pump do this for over 6 months until one day it finally decided to just die....while I was cruising down the highway 60mph and 45mins from home.

I know fuel pumps failing are very common on these engines, but how about leaky injectors?

And if it were leaky injectors, wouldn’t there be a rough idle or smell of gasoline in the engine bay?

Weak fuel pump can cause MPG issues too, right?

I can’t wait to throw a fuel pressure gauge on the rail (which arrives Monday), I’m just waiting on the new fuel filter, so I can get a before/after measurement.

 

[OR VietVet]

With my girl's TrailBlazer, you get the fuel pressure reading at the fuel filter mount, back at the tank area. Just threads on and get a reading. I just back up on a ramp and there it is.

 

[swathdiver]

This problem is very likely the fuel pump, it won't hold pressure anymore, has lost its prime and needs to be replaced. This is how the ones that I've encountered usually fail first.

 

[Fless]

I know fuel pumps failing are very common on these engines, but how about leaky injectors?

And if it were leaky injectors, wouldn’t there be a rough idle or smell of gasoline in the engine bay?

Weak fuel pump can cause MPG issues too, right?

I can’t wait to throw a fuel pressure gauge on the rail (which arrives Monday), I’m just waiting on the new fuel filter, so I can get a before/after measurement.

As you are changing the fuel filter (old one out, new one not yet installed) you could rig up the output of the fuel pump directly to the pressure gauge. Run the pump and monitor the leakdown right there.

 

[Rayyy]

As you are changing the fuel filter (old one out, new one not yet installed) you could rig up the output of the fuel pump directly to the pressure gauge. Run the pump and monitor the leakdown right there.

That's a great idea. Would I need a special fitting to accomplish this? I shall look into this.

 

[frydaddy96]

Just throwing this out there... check the rotor and cap if you haven't yet.
My '99 would start maybe crank an extra rotation but start on the first try. What got me looking though is driving the back roads, going up hills at 40 - 55 mph it would buck like the TCC was disengaging/engaging very quickly. It would also do it at 70 mph on the highway if enough load was placed on the drive train. Kept thinking it was the transmission. MPG was down a bit maybe but not alarming. It also seemed to have a rough idle, a little more vibes than what I remember. So I looked in my maintenance log, plugs had around 40K but the wires, cap and rotor were original with a bit over 200K on them. When I pulled the cap off, all 8 posts were covered in powder and the end of the rotor was corroded and burnt. Don't know how it was even getting a spark AND there were NO codes. No more bucking under load, starts better and will see what the mpg is after a couple of tanks.

 

[mattbta]

No distributor or optispark on an LS motor.

Just throwing this out there... check the rotor and cap if you haven't yet.
My '99 would start maybe crank an extra rotation but start on the first try. What got me looking though is driving the back roads, going up hills at 40 - 55 mph it would buck like the TCC was disengaging/engaging very quickly. It would also do it at 70 mph on the highway if enough load was placed on the drive train. Kept thinking it was the transmission. MPG was down a bit maybe but not alarming. It also seemed to have a rough idle, a little more vibes than what I remember. So I looked in my maintenance log, plugs had around 40K but the wires, cap and rotor were original with a bit over 200K on them. When I pulled the cap off, all 8 posts were covered in powder and the end of the rotor was corroded and burnt. Don't know how it was even getting a spark AND there were NO codes. No more bucking under load, starts better and will see what the mpg is after a couple of tanks.