Random Missfire Issues

[cjman250]

Ive have a 93 c1500 with a 350 and keep having issues with random fits where my truck will start missing while driving down the road or sitting at a stop light it will miss and then stall out. I have no check engine lights but I hooked up a scanner to it at O'reilly's and it had a pending code p0300 for random cylinder misfire. Ive been throwing parts at it (something I dont want to do and I know its not the smartest) and have installed the following:
- Distributor
- MAP sensor
- O2 Sensor
- Coolant temp sensor
This problem occurs completely randomly. I have driven it for a month without problems to have it act up for 3 days run fine again for a week. After the o2 sensor and the coolant temp sensor were put in the problem went away for probably 2 months and included a trip to Florida (1000 miles round trip) along with the truck being my daily driver (60 round trip). Now my issues are back and worse than ever. At this point Im lost at where to even keep looking and internet searches have come up with very little help. Any help is greatly appreciated.

 

[deven bullis]

Have you checked your intake manifold gasket to see if it needs to be replaced?

 

[98chevy2500SS]

Have you looked at your spark plugs? Did a whole bunch of work to my truck and found out cylinder 8 had a fowled out spark plug. Put a new one in there, runs like new again.

Here is my thread on the issue: http://www.gmt400.com/threads/random-cylinder-misfire.37906/

 

[chipskittles]

take all your spark plugs out. They should all look about the same. If they don't that will clue you in on the affected cylinders at least. What kind of distributor did you put in? They aren't all the same quality, especially the ICMs

 

[cjman250]

Ive have a 93 c1500 with a 350 and keep having issues with random fits where my truck will start missing while driving down the road or sitting at a stop light it will miss and then stall out. I have no check engine lights but I hooked up a scanner to it at O'reilly's and it had a pending code p0300 for random cylinder misfire. Ive been throwing parts at it (something I dont want to do and I know its not the smartest) and have installed the following:
- Distributor
- MAP sensor
- O2 Sensor
- Coolant temp sensor
This problem occurs completely randomly. I have driven it for a month without problems to have it act up for 3 days run fine again for a week. After the o2 sensor and the coolant temp sensor were put in the problem went away for probably 2 months and included a trip to Florida (1000 miles round trip) along with the truck being my daily driver (60 round trip). Now my issues are back and worse than ever. At this point Im lost at where to even keep looking and internet searches have come up with very little help. Any help is greatly appreciated.

Have you checked your intake manifold gasket to see if it needs to be replaced?

Sprayed around it with carb cleaner and had no idle surge or anything to make me believe it is leaking.

Have you looked at your spark plugs? Did a whole bunch of work to my truck and found out cylinder 8 had a fowled out spark plug. Put a new one in there, runs like new again.

Here is my thread on the issue: http://www.gmt400.com/threads/random-cylinder-misfire.37906/

Put new plugs in also, probably should've mentioned that.

take all your spark plugs out. They should all look about the same. If they don't that will clue you in on the affected cylinders at least. What kind of distributor did you put in? They aren't all the same quality, especially the ICMs

Changed the plugs since it started and they all looked the same, no fouling or anything like that. The distributor is a Delphi unit from rock auto.

 

[chipskittles]

Are you losing coolant? EGR valve ever been changed?

 

[98chevy2500SS]

Hmm... could be a bad fuel pump you are experiencing. I have heard the fuel pumps can cause this problem, and since yours in a '93, might want to check into one of those since your truck is getting a tad old. Check the fuel pressure and see what it is.

 

[cjman250]

Are you losing coolant? EGR valve ever been changed?

Not loosing any coolant, egr was changed a few years ago. I tried unplugging the vacuum line on it and it still has missing episodes.

Hmm... could be a bad fuel pump you are experiencing. I have heard the fuel pumps can cause this problem, and since yours in a '93, might want to check into one of those since your truck is getting a tad old. Check the fuel pressure and see what it is.

Haha the fuel pump actually went out about a month or so ago so it's also new. I didn't change the relay so I almost wonder if that could be the problem.

 

[Eskimomann209]

I say pop a precat 02 sensor

Bad catalytic converter can and will do that
And this test is free lol

 

[kauila]

A coil beginning to going bad could make the truck act the way you described.