Hesitation upon acceleration...

[DuallyGuy]

Hello! My trucks been doing this weird stumble when I press the gas pedal. It sounds like it wants to choke out and die but then it starts to accelerate. And just now I was trying to accelerate when not only did it stumble, but I heard what sounded like a back fire coming from the engine compartment. What gives?

 

[crazy4offroad]

Backfire through the intake usually indicates a vacuum leak, or a dead/dting ignition component (plug, wire, bad distributor cap/rotor).

 

[DuallyGuy]

Hmm...I just did the wires n plugs, but maybe I shouldve done cap n rotor too...is my timing a possible issue? Also I looked for loose vacuum lines but couldnt find anything disconnected. Unless theres vacuum lines hiding?

 

[crazy4offroad]

Yes. I'm not sure of what it should be set at though.

 

[89Suburban]

Hmm...I just did the wires n plugs, but maybe I shouldve done cap n rotor too...is my timing a possible issue?

It started doing this right after the install of the parts?

 

[Jims86]

Matt, your 454 should be set at 4*BTDC. Have you ever done the fuel filter? I agree with Vac leaks also.

 

[DuallyGuy]

No..its been doing it prior...

 

[crazy4offroad]

I would change the cap & rotor, check all your vac lines for dry rot/cracking/splitting, check the front & rear intake gaskets using carb & choke cleaner (spray it on and see if the idle spikes up), change fuel filters, and check the timing.

 

[DuallyGuy]

Thank you all for the info. On my way to get cap n rotor and carb cleaner. I will follow the instructions to search for any vac leaks. My buddy is gonna set the timing. Thanks for the timing Jim. To be continued...thanks everyone! Oh and fuel filter was replaced also.

 

[Jims86]

Thank you all for the info. On my way to get cap n rotor and carb cleaner. I will follow the instructions to search for any vac leaks. My buddy is gonna set the timing. Thanks for the timing Jim. To be continued...thanks everyone! Oh and fuel filter was replaced also.

Hey, one more thing. When you are on that distributor, make sure the vent screens in the bottom are clean...if not, moisture gets trapped under the cap, and you being where you are, that moisture usually is salty, and promotes corrosion. If the New parts dont cure the problem, i would suggest a compression check, to rule or find out the worst...whatever the case may be. Try to look at your exhuast in the mirror on a deserted road somewher..Maybe somwhere up by Lopez Canyon Rd...dunno how traffic is there, and see if it is smoking during the hesitation, you may have an injector thats a little drippy.

 

[DuallyGuy]

Roger that. My friend cleaned the throttle body when we replaced the injector connectors. He said the injectors looked good. The truck recently passed smog also. I dont see a sign of any smoke whatsoever from the tail pipe either.

 

[Jims86]

Matt, how does your truck idle? Maybe disconnect the EGR and see if it happens again. If there is vacuum to the EGR at the wrong time, and there is no smoke, there is a good chance that your EGR valve solenoid is thrashed, and letting vac through uncommanded from the ECM.

 

[DuallyGuy]

**update**

Ok...It's been a couple days. My progress has been slow and painful! I got a hold of a timing light and discovered that the truck was running at 16 BTDC! So I adjusted it to 4 BTDC. It seems to have brought the idle down a tad too low though. The hood has a slight shake in it. I may have to re-adjust my TPS since I recently replaced that and I dont think I did that right in the first place. I replaced the Cap and Rotor also which by the way was THRASHED! Both cap and rotor were on their last legs. I just bought this truck and I'm discovering all of the half assed things that the previous owner did. I bought the carb cleaner to spray along the intake and vac lines to detect any leaks but haven't done that yet since my friend recommended I do that when the engine was cooler. (We did these repairs in 100 degree weather.) And then to top it off, I put my Lance Camper on my truck to get ready for camping this weekend. And what decides to happen? I blow an exhaust manifold gasket. So I'm assuming I should start another thread for that one, because I'm discovering how hard it is to locate a manifold gasket for 'smog legal' headers. Any suggestions?

 

[Jims86]

Ok...It's been a couple days. My progress has been slow and painful! I got a hold of a timing light and discovered that the truck was running at 16 BTDC! So I adjusted it to 4 BTDC. It seems to have brought the idle down a tad too low though. The hood has a slight shake in it. I may have to re-adjust my TPS since I recently replaced that and I dont think I did that right in the first place. I replaced the Cap and Rotor also which by the way was THRASHED! Both cap and rotor were on their last legs. I just bought this truck and I'm discovering all of the half assed things that the previous owner did. I bought the carb cleaner to spray along the intake and vac lines to detect any leaks but haven't done that yet since my friend recommended I do that when the engine was cooler. (We did these repairs in 100 degree weather.) And then to top it off, I put my Lance Camper on my truck to get ready for camping this weekend. And what decides to happen? I blow an exhaust manifold gasket. So I'm assuming I should start another thread for that one, because I'm discovering how hard it is to locate a manifold gasket for 'smog legal' headers. Any suggestions?

The best suggestion I can make, is to return the truck to cast Iron manifolds, you cant beat them for durability.
Since you re set your timing, disconnect the battery for 15 seconds, then reconnect and drive. idle shoul be in the neighborhood of 625+/-25 in drive. GM truck usually idle pretty low.
On the ignition side, make sur you didnt mix up 5 and 7....very easy to do.

 

[DuallyGuy]

Gotcha, Thanks!