Random misfire Help?

scooter5991 · 12-20-2006, 12:33 PM

I have a 1997 Blazer with a 4.3 L and 180,000 miles. The truck will start fine and for the most of the time will idle smoothly. Under acceleration you can feel a misfire occasionally. The big misfire comes when I am driving at 60mph or above. Thats when the check engine lit will come on and sometime it starts flashing. The truck has been sitting while I have been working on this problem. So in the last 5000 miles the fuel pump has been changed.(1 1/2 yrs ago) Since this issue has come up I have changed the plugs, wires , cap , rotor,(1 yr) egr valve. There was a egr code that was coming up so I replace the valve.(6 months) Now the code is just for the random misfire. I have some time this christmas weekend so I thought I might take another stab at it but I have tried what I know and now I have no direction. If somebody has a direction it would be appreciated. Also I will double check the egr code to make sure it is gone, but I need to get my scanner back over chrismas. Thanks again Scooter

Chris Stewart · 12-20-2006, 07:42 PM

Get the code and we'll have a better idea.

ericn1300 · 12-20-2006, 09:27 PM

A flashing check engine light indicates a misfire that if not corrected soon will take out the cat converter. Start with a complete tuneup including new plug wires

seadog95 · 12-20-2006, 09:56 PM

I had a random misfire code on my 01 blazer and ended up changing the fuel pressure regulator and two injectors, at the dealer for 710.00 dollars.

scooter5991 · 12-21-2006, 10:03 AM

I will get the codes this weekend and I have replaced the fuel regulator at about 70,000 miles. I was thinking about that but last time it had the same code but it ran rough at a idle and got smoother as I drove. Thanks for the help so far!!!

MT-2500 · 12-21-2006, 10:43 AM

Quote:

Originally Posted by scooter5991

I will get the codes this weekend and I have replaced the fuel regulator at about 70,000 miles. I was thinking about that but last time it had the same code but it ran rough at a idle and got smoother as I drove. Thanks for the help so far!!!

Get it put on a good engine capable scanner.
Check all present and past codes and sensor readings.
And check the camshaft timing retard setting. It should be less than -3 or +3
What kind of plugs did you feed it?
How is that fuel pressure?
And post back all codes.

scooter5991 · 12-28-2006, 10:40 AM

Hello,

I had to put in a new battery this weekend. It started fine and I had to run it about 12 miles before the check engine lit come on. I could feel it miss while driving an also when I hold down the pedel and bring the RPM up.
Last night when I got home I scanned the truck and when I started the engine the check engine lit was flashing. I revved it a couple of times and it stopped flashing. The scan code was P300 radom misfire all cylinders. The plugs I have are AC Delco and I do not have a gauge for fuel pressure but the is a fairly new fuel pump and I even changed the filter again to make sure. My scan tool is not a good one, so I can not check the sensors. Do you think it could be the fuel regulator again? Do I just need to bring it in?
Anything else it could be? NOTE : The last time the regulator went out it ran fine at highway speeds but idled rough.

Thanks,
Scooter5991

MT-2500 · 12-28-2006, 11:54 AM

Quote:

Originally Posted by scooter5991

Hello,

I had to put in a new battery this weekend. It started fine and I had to run it about 12 miles before the check engine lit come on. I could feel it miss while driving an also when I hold down the pedel and bring the RPM up.
Last night when I got home I scanned the truck and when I started the engine the check engine lit was flashing. I revved it a couple of times and it stopped flashing. The scan code was P300 radom misfire all cylinders. The plugs I have are AC Delco and I do not have a gauge for fuel pressure but the is a fairly new fuel pump and I even changed the filter again to make sure. My scan tool is not a good one, so I can not check the sensors. Do you think it could be the fuel regulator again? Do I just need to bring it in?
Anything else it could be? NOTE : The last time the regulator went out it ran fine at highway speeds but idled rough.

Thanks,
Scooter5991

Fuel pressure or fuel trims can lead to a miss fire.
But if you can feel it and a code is setting work on the plugs and wires and cap end first.
A good OBD11 scanner should give you a code for the cylinder that is miss firings. Which would help narrow it down.
If you can not spot it by looking at plugs and wires or cap.
Some auto parts places like AZ give a free code check that may show a code for what cylinder or cylinders the miss fire is on.
What no Ac plugs and what gap did you set them at?

muddog321 · 12-28-2006, 01:59 PM

P0300 is a bear to find the cause. Could be cap/rotor/plugs/wires then the coil or cam sensor, egr, vac leak (leans out) or after fighting mine on and off was a bad crank position sensor which I had changed with a Wells (do not use these parts) - even did a TPS as mine was also failing - never got any codes until 1 month later and a p0339 so changed my crank sensor again for a Standard Motor Products sensor and all fixed. Started having a full throttle rattle which pointed to timing so that Wells crank sensor must have thrown that off - specs were probably sloppy so not aligned right - only goes in one way.

larrym0001 · 01-07-2007, 02:38 AM

Sounds like the injector poppets are dirty to me. Get some techron injection cleaner and throw it in the tank and drive it like you stole it. Larry

Scrapper · 01-07-2007, 08:11 AM

i agree..put injecter cleaner in it and drive like you stold like he sais..but i use sea foam in my cars trucks and my bike..it's good stuff...good luck....

SCRAPPER...

ericn1300 · 01-07-2007, 04:24 PM

I don't agree, doesn't sound like a fuel system problem. as much as i love and recommend Techron, you're chasing an ignition problem. check the distributor bearings.

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