I've spent a solid month browsing these forums in search of an answer to my stutter/sputter rough idle on my 97 4.3 liter..


First let me tell you the symptoms, Blazer starts hard like it's cold after maybe 3 or 4 tries.

There is no ses light, nothing. There was a tps code its gone now.

At only the first 1/8 of the throttle upon take-off it sputters, sometimes 1/4 throttle, you can hear the motor chugging sputtering from the tail pipe like it's struggling to breathe.

When I lay into the throttle, real good she comes right out of it like the blazer was brand new... Often it will stutter at higher speeds but thats only at the very little throttle needed to make it coast...

I have recently had 4 mechanics work on my truck. I've had 2 triple A inspections done, a fuel pump pressure test, I've had all of my o2 sensors replaced, Spark plugs, and wires. Exhaust is perfect, cat too. I have a ton of stuff done to it.

It only started doing this a couple months ago around the 3rd or so mechanic to look at it.

I have a cold air intake, no oil. I have cleaned the maf, unplugged the maf. Still problems.

I have cleaned the EGR valve, still no go.

I have changed the Tps sensor because it was throwing a code. Not anymore.

I have cleaned the top of the carb, the Breather , the throttle body itself.

I have tried disconnecting the battery for a bit... Idk someone said they had luck with this, I have no idea why it would do anything AT all.

I have put dry gas in it thinking I got some bad gas... I have filled the truck atleast 10 times now tho.

I have some pretty ****ty gas mileage too, around 16 ish. Truck has 150k miles stock tires and rims and I hardly ever get into the throttle... Should be more around 18-20 I would think.

Earlier in the year when it would rain, the symptoms would get worse.. So I had 1 of the mechanics look at the dist. cap. He said it was fine, they sprayed it and everything... all good.

I am wondering if the fuel injectors are crapping out? Since I've heard the Spider injection system is ****... But wouldn't I be atleast getting some sort of code if that was the case?

Does anyone have any ideas, I repeat... no codes, pressure good, don't need to take it to anyone for tests... Just some ideas or thoughts of what I should try next. Besides if I have to spend 300 more bucks I'm going to buy a moped... instead.

 

To me, this screams of ignition system issues. What brand of parts were used in the tune up (plugs, wires, cap, & rotor) the last time it was done? Many members have chased their tails, replacing countless components, spending hundreds of dollars all while attempting to fix this very concern. Many have found that poor quality aftermarket ignition components that were installed as an initial tune up contributed to the overall problem and the thought of those brand new components being the problem never crossed their mind. These trucks seem to operate best with AC Delco caps & rotors.

Has the distributor been removed and the driven gear on the bottom inspected? If so, was Cam Retard checked/set upon installation of the distributor into the engine?

Plugged up poppet nozzles could also be contributing to your problem. A mechanic that knows how to use a scan tool properly can run an injector balance test during which each injector can be opened on command. This test can be performed with the upper plenum off and the fuel lines reconnected to the spider. With the injectors directed into a small clear container, their output can be observed to tell if they are operating properly. A fine mist should shoot from the tip of the poppet nozzle. If you have to replace more than 2 injectors, it becomes more cost effective to just get the updated MFI spider which does away with the often problematic poppet nozzle setup.

 

Everything is Ac Delco. I wasn't chancing it. The dist cap is new, nothing with the dist has been touched and was working fine, for about 4 months. I had a mechanic check the dist cap out, he clearly stated that there was nothing wrong.

I did have one garage tell me they thought that because my fuel gauge was surging that I needed a new fuel pump, I just laughed because little did they know I had just had it tested the day before. I really hope it's not the poppets misting, I've only seen what the spyder looks like and it's freaking scary man, scary.

 

I just fixed a blazer doing the same exact thing yours is doing.
Come to find out the intake gasket was blowed.it was sucking air the whole time and it was barely leaking water
to where it wasnt showing any leaks but we kept losing 1/4 of a gallon every month or so and when pulling out it would sputter until u got down on it.
and it would also do it at high speed when your barley hitting the gas to coast like you said.So if u haven;t fixed it yet that may be your problem.

 

Where was it sucking air? At an intake port? From outside or the cam valley?

Just curious.

To find a vacuum leak, outside the engine I disconnect the IAC with the engine warm and adj throttle enough to keep it running. {Remember how much and what direction and be sure to restore}
Then take an UNLIT propane torch around any and all suspected vac leak areas. If the rpm changes then that's where the leak is.

 

I believe I have found the problem, I never noticed it before because I have never opened my hood at night. Never occured to me that maybe I had a damaged spark plug wire and it could be arcing.

I stopped after getting home late last night pitch black out, with the truck running I opened the hood. I immediately saw that the Coil wire running to the dist. cap was arcing. Bingo. Getting spark plug wires tommorow will update at some point. Hopefully the coil is still good.

 

Add a mist of water to it and you'll probably be surprised. But yeah, a spark leak will be highly visible in the dark!! Glad you found the problem and it was something fairly simple!

 

Well changed the spark plug wires and coil to dizzy wire this morning before work.
Didn't work.

I think my coil is now arcing, when I got home tonight I opened the hood and saw the same thing from last night.

Still starting hard, and sputtering.

Oh and My dash lights quit on the way home. Yay, for me.
I love this truck but this has got to be the most annoying truck I have ever owned thus far.
will update if anything changes.

 

I read that you tested the fuel pump, and the pressure was good, did you do a leak down test? to see if the pressure held for at least 10 minutes.

Those symptoms sound just like a leaking FPR.

 

A new a spider injector set will come with new fuel regulator. If you see clean areas around the back of the top end of the intake manifold after removing the upper plenum... then the fuel regulator is bad...check your injectors closely before taking the plenum off. These are notorious for going bad.