2001 Silverado V6 - slow start, hesitation on highway?

[zeitgeist57]

My 2001 Silverado 1500 - 4.3L V6/4L60E/2WD - has 79k miles on it and two annoying items:

1) Cold start can crank upwards of 5 seconds before it catches.

2) Noticable bucking/hesitation at highway cruising speeds.

 

I just replaced cap/rotor/wires/plugs, and one of the spark-plug wires was contacting a bracket, rubbed the insulation off and was clearly arcing. Acceleration cleaned up dramatically, but cold start and highway cruising still remained. Spark Plugs looked tannish-brown...very clean in all but one cylinder; figured the arcing may have contributed to that.

 

I haven't done the fuel filter yet...next on my list.

 

I can't find the fuel pressure regulator. Would love to gauge start-up fuel pressure.

 

I'm confused because most of my googling says that:

1) If it's electrical, it would cause a misfire enough that I may smell fuel, or hear it. The truck idles like a sewing machine.

2) if it was fuel, it would likely hesitate more at idle, acceleration.

 

Any thoughts? Thanks in advance, CR!

[Grudes]

These trucks also had problems with the ECM's going bad and causing problems like this

[Geeto67]

I have a HF fuel pressure gauge you can borrow. It screws right into the rails and can tell you the pressure at startup.

 

My money is on fuel filter, maybe even an external one that was added. A partially blocked one will sometimes cause hesitation during constant highway speed running if you are above 2k rpms for a consistent period of time.

 

Here is another thought - what is your battery gauge doing at the time? I had a hesitation in my jeep similar to what you are describing and it turned out to be a voltage regulator going bad. It would occasionally dip the voltage below 9v causing a full ignition flame-out only to immediately pick up and continue running with the next beat. replaced the regulator and it went away. It was inconsistent when it would happen but I would notice it more when I was at highway speeds.

[Coaster]

Sounds similar to my 1999 just before I lost my fuel pump.

[Red Beard]

Definitely sounds like a fuel delivery more so than spark. Simply because of the sewing machine idle. I would start with basics and go from there. Fuel filter, check fuel pressure. If the pump is weak (starting to go) it may have enough pressure to idle but not enough to run at high rpm's.

 

Also it could be an issue with the coil itself. My old 4.3L s10 had an issue with the coil going out. At idle it would be fine, once you started hitting a higher rpm it would start shorting out through the insulation on the coil itself. Had the same issue on my 240 causing the coil to ground out the the block/bracket instead of going to the spark plug.

[zeitgeist57]

Thanks, guys. Should've mentioned I drilled out the two rivets - bracket holds Ignition Control Module, aluminum heat sink, and Coil together - and screwed in a new ignition coil. That helped with running, which is why I am thinking it may be fuel delivery.

 

I've also heard that the fuel pressure regulator can go bad on these...

 

The only thing that makes me question fuel is if I turn the key to let it crank over 3-4 times (maybe a second), then I click the key down to ACC, wait a second, then crank it again it fires right off. Seems almost like that is electrical, not fuel.

[Coaster]

Thanks, guys. Should've mentioned I drilled out the two rivets - bracket holds Ignition Control Module, aluminum heat sink, and Coil together - and screwed in a new ignition coil. That helped with running, which is why I am thinking it may be fuel delivery.

 

I've also heard that the fuel pressure regulator can go bad on these...

 

The only thing that makes me question fuel is if I turn the key to let it crank over 3-4 times (maybe a second), then I click the key down to ACC, wait a second, then crank it again it fires right off. Seems almost like that is electrical, not fuel.

 

My truck I had to turn the key to run for 15 seconds or so before it would start when the fuel pump was going out. Kinda like a glow plug

[spankis]

This is only slightly helpful (maybe not at all), but I worked with an electrician who had an '04 with the 4.3L that did the same shit. Ran great, but would regularly take 10-20 seconds to crank before firing, and other times wouldn't start at all. As an electrician he did all the electrical diagnosis but never did find the issue, at least not in in the several months I was working with him...

[Cordell]

Start with a fuel pressure gauge, should be 58 PSI, see if its dropping under load. Likely a fuel pump, pretty sure those still have a fuel filter on the frame rail (newer ones don't) so change that regardless. If there's a feed and return coming off the rail the regulator is on the rail (probably this), otherwise trucks after that are returnless and the regulator is part of the sending unit in the tank.

 

Also beware of aftermarket distributor caps, cheaper caps have a tendency to arc inside the cap where they cross each other. I wouldn't buy anything other then a GM cap, maybe NAPA. Some cheap shit won't last long if it doesn't start screwing up as soon as you install it.

[zeitgeist57]

I have the fuel filter, located on drivers' frame rail - will replace.

 

You KNOW I bought a cheap cap/rotor Will get an ACDelco replacement if the fuel filter doesn't affect the driveability.

[Red Beard]

Not to mention, a LOT of the early 2000's chevy's had a long start when they got up in age/mileage. My buddy had a 2003 with the same set up and his was almost comical how long it would take to start, usually 2-3 "normal" cranks to start. But also turning the key on and letting the fuel pump prime for a second would help it to start faster.

 

I do agree with what you are suspecting. It does sound like fuel, weather that be the pump not having enough pressure, the fuel filter / injectors being partially clogged.

 

If it were the FPR however, it would make for a more consistent issue even at idle. The regulator is meant to limit the pressure from the pump, so if that were out, It would run pig rich even at idle, and would hesitate severely when you gunned it (may even stall).

 

I would check the timing too, with you changing the cap and such it may have thrown off the timing enough to mess with it under load, not likely but doesn't hurt to check it off the list just in case.

[RS69]

Sounds like the fuel pump... Need to see verify fuel pressure.

[xlr8tn]

I agree with the fuel pump guys...I had a 98 years ago with same symptoms and was fuel pump.

[zeitgeist57]

Replaced the fuel filter aaaaaand..............*drum roll*..................

 

No change.

 

I need to check on the rattling flexplate: replace it if it's cracked or tighten the TQ conv bolts...then I need to replace the 2 driveshaft u-joints...then I need to install my new MaxTrac 2/4 drop kit:D...THEN I'll replace the fuel pump. #priorities

 

A couple of Youtubers said to pull the bed to access the tank for fuel pump replacement. Is that others' experience?

[DavidBaustert]

Mine has this same "bucking" during cruise. I honestly think it might be in the suspension. Kinda feels like a misfire/bucking but I'm questioning shocks.

[zeitgeist57]

Mine has this same "bucking" during cruise. I honestly think it might be in the suspension. Kinda feels like a misfire/bucking but I'm questioning shocks.

 

So, the other thing is my driveshaft u-joints are toast; super-squeaky at low speed until the RPMs get up and then it goes away. Wouldn't be surprised if it's out-of-balance spinning away at highway speeds. I've got new Dana Spicers so we'll see what that may do.

 

It's not so much bucking, as it is fading in and out of thrust at steady engine speeds on the highway, if that makes sense. Acceleration is steady when the pedal is pressed, though now my butt-dyno is convinced that the fuel flow is affecting performace.

[Cordell]

Have you checked fuel pressure? Of all the cheap people, why would you throw a fuel pump at it if you don’t know if it needs it or not?

[zeitgeist57]

Have you checked fuel pressure? Of all the cheap people, why would you throw a fuel pump at it if you don’t know if it needs it or not?

 

Good point. You're right though, Scott. I won't swap the pump without checking pressure first. what I should've said is I'm going to table the fuel pump until I've done some other projects I already have the parts for.

 

https://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/how-to-test-the-fuel-pump-1

[Geeto67]

still offering to lend you my fuel system pressure tester kit. It screws into the bleeder/test port on the top of the engine.

 

https://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/how-to-test-the-fuel-pump-1

[Crossle]

Has anyone mentioned a fuel pump yet? That's my internet guess.

[Green Bastard]

Another vote for checking fuel pressure.

Also, is this the same 4.3 that was used in Blazers and the S-10 trucks that had issues with the fuel spiders (that would cause a long crank)? Also, is there a cel you could have checked?

 

Has anyone mentioned a fuel pump yet? That's my internet guess.

 

Probably a head gasket. It's always a head gasket with internet diagnostics.

[Geeto67]

Another vote for checking fuel pressure.

Also, is this the same 4.3 that was used in Blazers and the S-10 trucks that had issues with the fuel spiders (that would cause a long crank)? Also, is there a cel you could have checked?

 

 

same engine, LF6/L35 - 1996 to 2002.

 

What's fascinating about that engine BTW is that the engine family (90degree v6 based off the v8 small block) was in use from 1978 to 2014 - and was the last engine family based off the original 1955 small block v8 architecture. The new 4.3 EcoTec3from 2014+ is based off the LS/LT1 v8 architecture and makes almost 100hp more.

[xlr8tn]

I know when mine went I noticed the lack of power at highway speeds first and then the long cranks. When I checked fuel pressure it was only a pound or two below spec (which I forget what it was). After the pump it was good to go. Yep...those spiders are also known to leak. You can shine a light in the intake and see if the walls are washed down with fuel. I'm still going fuel pressure though. Another notorious issue is the lower intake gasket...if it's not leaking now it will.

[zeitgeist57]

still offering to lend you my fuel system pressure tester kit. It screws into the bleeder/test port on the top of the engine.

 

https://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/how-to-test-the-fuel-pump-1

 

Kerry, will take you up on that offer. I’ll reach out. Thank you!

[POS VETT]

So, the other thing is my driveshaft u-joints are toast; super-squeaky at low speed until the RPMs get up and then it goes away. Wouldn't be surprised if it's out-of-balance spinning away at highway speeds. I've got new Dana Spicers so we'll see what that may do.

 

It's not so much bucking, as it is fading in and out of thrust at steady engine speeds on the highway, if that makes sense. Acceleration is steady when the pedal is pressed, though now my butt-dyno is convinced that the fuel flow is affecting performace.

 

Might want to address the U-joints very soon. I had that noise on my old '3 and it was caused by one (or more) cracked trunnion.