Truck stutters

[voltagexdt 10+ year member]

I posted this about a year ago and still have same issues.

Here's what's going on.

The engine will stutter or backfire while my subs pound.

Here's my setup

91 chevy 350 single cab.

Powerbass 2200 watt amp

2 powerbass 3xl 12s

2 red top optimas

1 yellow top optima

1 300 amp dc power alternator

1 oem 110amp alternator

What I have done

Under hood are both red top batteries and both alternators

Behind seat is yellow top under seat is amp

Oem alternator runs "main" battery. Truck runs from that

HO alternator is hooked to second red top and that battery is linked to yellow top in rear

Now for safety I have a 300 amp breaker that is under hood and can break the line to rear battery.

The amp is directly hooked to the rear battery.

Now like I said when I crank the amp up the truck will die or stutter or backfire

I have upgraded most engine components thinking I was rattling something loose.

But one day I tried something to test if it's a rattle issue.

The breaker under the hood I'm using to safety the rear battery I can disconnect

The removes everything under the hood for my system and is purely amp to rear battery

System cranks loud truck runs without issue.

Of course system only cranks until battery dies

When truck is running I'm at 14.5 volts main batt and 14.5 for both sub batteries

My theory is the alternator is slowing the engine via the serpentine belt.

I have also tried various battery alternator set ups. Ie all 3 batteries together on the HO amp.

Been doing car audio systems for 20 years and this blows my mind

Please advise

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[jrdnhsnbrg 10+ year member]

1. Circuit breakers are not ideal.

2. Time for a new truck.

 

[voltagexdt 10+ year member]

Anyone with real help?

 

[brian84corvette 10+ year member]

i can only tell you that the computer and engine managment system on my 1990 chevy 2500 pick up truck was awfull.

so

me being super smart i bought a 1990 chevy suburban. seems to run better - but still ocasionaly "surges" the idle but no where near as bad as the truck did.

my guess

ground.

the computer is getting some strange feedback thru ground - causing one or more sensors to read strangely during bass = truck dies.

possible solution - create redundant grounds everywhere. the more the better. see if it helps. investigate the idle air control valve. mine gave me problems since i first got the truck. replaced it 3 times in 4 years. it still gave me issues of that surge at idle but it was bad in the truck. like 3krpm at times.

hope you get it figured out.

if not = put on a carburator and enjoy more performence / less gas mileage

also this truck is notorious for having the intake gaskets leak coolant at around this age of them. if its possible you are leaking coolant down in the engine block - it will evaporate and have to steam up and out the pcv valve in to the intake and thru the engine. it runs strange when this happens so keep an eye on the coolant levels.

 

[CrossoverOre 10+ year member]

might have something to do with the spark plugs no getting enough power from the coil maybe

 

[LOUDNDEEP 10+ year member]

so looking thru your old thread you already checked the fuel pump and its connections, you replaced o2 sensors and it helped but now its doing it again? have you disconnected the ecu and cleaned the connector and applied dielectric grease? with a 20+year old vehicle it could be an electrical nightmare.wire sheathing gets brittle and the vibrations could be causing a wire to ground out, i would check every connection and clean and grease each one. you might have to go thru the wiring and check for breaks in the sheathing or look at the ecu and see if anything is loose internally, good luck

sorry just reread your post. do have the ability to check voltage at the coil while not at full tilt to see if your spark is getting weaker when the bass notes hit? also does your idle slow noticeably before it stalls? have you tried to up your idle? these are all just guesses and i could be totally wrong

 

[Dub7sonoma Premium Member]

So it only does it when your subs are turned way up? Is the truck a standard?

 

[voltagexdt 10+ year member]

Ok truck is a standard 350 TBI

I replaced computer

But again if I disconnect all charging from rear battery the truck and system runs fine but rear battery dies

Also for grounds I have added about 9 8 ga grounds all over

If stopped at idle. 700 rpms

Subs pounding can drop to 300 or die.

If I leave all batteries connected but simply unplug the connector from the alternators again truck runs great

I hit 153.7

I state this because it would defiantly vibrate something

With no charging devices running I still hit 150-145 as battery dies but again truck runs great

Spark plugs new

New msd wires cap

Not sure if I mentioned this but before when I had single battery single alt same issue

Then I began to add batteries in vein

Then new alternator in vein

Was gonna go out buy high end xs power or kinetics. But that's a possible waiste again.

I tell u what if you guys are able to fix this for me I'll paypal some serious money for the fix an knowledge cause this is so frustrating

 

[Dub7sonoma Premium Member]

Ok truck is a standard 350 TBII replaced computer

But again if I disconnect all charging from rear battery the truck and system runs fine but rear battery dies

Also for grounds I have added about 9 8 ga grounds all over

If stopped at idle. 700 rpms

Subs pounding can drop to 300 or die.

If I leave all batteries connected but simply unplug the connector from the alternators again truck runs great

I hit 153.7

I state this because it would defiantly vibrate something

With no charging devices running I still hit 150-145 as battery dies but again truck runs great

Spark plugs new

New msd wires cap

Not sure if I mentioned this but before when I had single battery single alt same issue

Then I began to add batteries in vein

Then new alternator in vein

Was gonna go out buy high end xs power or kinetics. But that's a possible waiste again.

I tell u what if you guys are able to fix this for me I'll paypal some serious money for the fix an knowledge cause this is so frustrating

Its the drag created from your alternator. You don't feel it surge when the clutch is pushed in or when your in neutral right? I have a 5 speed in my Sonoma (4.3L v6) with dual alternators. When the amps are drawing a ton of power it puts more strain on your electrical and makes the alts work harder. If im just idling about 5mph in 1st gear and turn my system up a ton.... It almost stops the truck. But its definitely the alternator

 

[Dub7sonoma Premium Member]

If you want to get technical...

The voltage coming out of the alternator depends on two variables: the amount of current flowing through the field coil (i.e. the strength of the magnetic field) and the speed at which the alternator’s field is rotating. You are feeling so much surge at lower RPMs because the alternator is trying to create a stronger Electromagnetic Field (EMF) to increase its output. Which creates greater resistance and more strain on your motor. That's what is causing the motor to loose rpms and feels like it stutters.

 

[Popwarhomie 5,000+ posts]

Throw a bigger crank pulley on it.

Have you tried to pull the codes?

 

[Slo_Ride 5,000+ posts]

"Truck Stutters"

Mine wont even talk to me. Speech therapy?

 

[voltagexdt 10+ year member]

Its the drag created from your alternator. You don't feel it surge when the clutch is pushed in or when your in neutral right? I have a 5 speed in my Sonoma (4.3L v6) with dual alternators. When the amps are drawing a ton of power it puts more strain on your electrical and makes the alts work harder. If im just idling about 5mph in 1st gear and turn my system up a ton.... It almost stops the truck. But its definitely the alternator

ok that's what I was kinda thinking.. but how do I fix this?

 

[voltagexdt 10+ year member]

Throw a bigger crank pulley on it.
Have you tried to pull the codes?

please explain how that would work.. mechanics im not so good at

 

[akheathen Premium Member]

actually, alternator feeds its field from the stator output after start-up, fyi.......

i noticed that you said there were a bunch of 8awg grounds for a 400a system. i believe that is your problem right there. the ground strap from the back of the left head to the firewall is likely toasted by now. at the least, you should have 3 runs of 4awg from the engine to the firewall, or equivalent in other wire size. under 10.5v and your fuel injectors shut off, and ignitor power is weak for the coil. on top of that, you may have damaged the ground runs to the ecu and body, hopefully not internally in the ecu, if this is the case. these trucks can actually run real nice, and be especially good to drive as a manual. only thing i don't really like is the decay rate and small/slow response of the iac valve. normally, if they do give you a problem, you just clean them out with throttle body cleaner and they work like new...... same goes for all of them between then and now. the tps is common to need replacement, and the ignitor around the same time as the fuel pump (100-150k) only real reason to put a carb on it is if you have no means to tune the ecu for whatever engine work you do....... even then, that comes down to lack of know-how, as a tunercat, or efilive/similar tuner is cheaper than a gen2 intake and carb, not to mention you would want to throw a stand-alone ignition in there, like a hei, or aftermarket, as the stock timing advance is done via ecu...... i digress....

long story short: upgrade your engine grounding, and complete the system as a single system, at least in the grounding of everything, and i would suggest you do a pinout from the ecu to grounds/ignitor/block. good luck.