1997 jimmy 4.3. I have code p0300 random misfire


donhand1
09-30-2009, 02:18 PM
I am having the same problem 1997 jimmy 4.3. I have code p0300 random misfire,I have new wires ,cap, rotor,plugs even changed the CPI. Have good fuel pressure(new pump & filter).As far as timing it checks on the mark. Just started when I put differnt engine in it.At first it ran fine then at about 30 days it just strated to miss,it will smoke the tires on take off just misses at slow throttle or constant speed.I'm about moneyed out unemployed also have changed all sensors and distrbutor.HELP?

MT-2500
10-02-2009, 01:19 PM
I am having the same problem 1997 jimmy 4.3. I have code p0300 random misfire,I have new wires ,cap, rotor,plugs even changed the CPI. Have good fuel pressure(new pump & filter).As far as timing it checks on the mark. Just started when I put differnt engine in it.At first it ran fine then at about 30 days it just strated to miss,it will smoke the tires on take off just misses at slow throttle or constant speed.I'm about moneyed out unemployed also have changed all sensors and distrbutor.HELP?

Start your own New thread and answer some of the upper questions?

donhand1
10-16-2009, 11:50 AM
OK I changed the fuel pump( again )it goes to 62lbs. when the key is turned on and holds 60lbs. after the pump is turned off for about 10 mins. never does leak all the way down,well not after 30 mins. Have checked for vacuum leaks none.The abs light came on about the same time it started all this P0300 stuff,could this cause random missfire?.

MT-2500
10-16-2009, 06:59 PM
OK I changed the fuel pump( again )it goes to 62lbs. when the key is turned on and holds 60lbs. after the pump is turned off for about 10 mins. never does leak all the way down,well not after 30 mins. Have checked for vacuum leaks none.The abs light came on about the same time it started all this P0300 stuff,could this cause random missfire?.

No on ABS light.
Any other codes?
Are you still getting the code after code clear?
Can you feel a ENGINE MISS?
Has the camshaft been set?
How is plugs and wire and cap and rotor?
AC delco plugs?

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

donhand1
10-19-2009, 05:56 PM
I checked out all the readings are within range of your specs. , but now I hooked it up to my son's snap-on Solus Pro.it showed hundreds of miss fires around the block,but then when we got back, I got behind the wheel and it runs great,I didn't do anything and did not change anything with the Solus.The only thing which was strange it showed engine temp.only got to 90 deg. most of the time it stayed at 85deg.will a bad temp.gauge make it run bad & misfire.

MT-2500
10-19-2009, 06:04 PM
I checked out all the readings are within range of your specs. , but now I hooked it up to my son's snap-on Solus Pro.it showed hundreds of miss fires around the block,but then when we got back, I got behind the wheel and it runs great,I didn't do anything and did not change anything with the Solus.The only thing which was strange it showed engine temp.only got to 90 deg. most of the time it stayed at 85deg.will a bad temp.gauge make it run bad & misfire.

Yes it could.
Have you checked the camshaft retard setting?
How are plugs and wires and cap and rotor?
Good hot blue spark to all plugs?
Is it missing on all cylinders or just certian ones.
What are codes no. with solas pro?
Also Be sure to run the full fuel pressure test after the new fuel pump.

donhand1
10-19-2009, 06:33 PM
only code is P0300 yes on all cylinders,but at this time it is not missing at, all my son said the computer works off of the temp sending unit ,but he said to check for a ground that might have reconnected it self some how.the camshaft retad is -14 by the solus it says it should be 0to -/+2.the plugs are new cap/rotor is new plug wires are all new(top of the line too) spark is blue and strong.

MT-2500
10-19-2009, 06:48 PM
only code is P0300 yes on all cylinders,but at this time it is not missing at, all my son said the computer works off of the temp sending unit ,but he said to check for a ground that might have reconnected it self some how.the camshaft retad is -14 by the solus it says it should be 0to -/+2.the plugs are new cap/rotor is new plug wires are all new(top of the line too) spark is blue and strong.

The solas pro in engine spefic should read out what cylinders are missing.
And set a code for each one missing.
Also if camshaft retard is at -14 there should be a code set for it to.

-14 camshaft retard will cause miss fires.

Set the camshaft retart to 0 or as close -1-2 0r +1-2 as you can get it.
When adjusting it you will need to speed engine up over 1K rpm for the new reading to read out.

And get thhe temp sensor reading right.
Let us know how it goes.

donhand1
10-28-2009, 12:04 PM
OK I got the timing with in 5 deg.,put on new temp. sending sensor.The temp. gets to about 158deg. , but it still misses.It is all thru the range cold or hot.Sometimes when I leave it run for an hour or so it does seem to run a little better,but still gives code P0300.the snap-on tester shows that all the cylinders are missing about the same thru a 255 miss-fire cycle,pulled another vacuum, does not show leak,compression is good on all 6 cylinders.I start auto tech classes in jan.maybe I will just wait and see if the instructer can figure it out,but if anyone has anything I can try I will.

MT-2500
10-28-2009, 12:34 PM
5 degrees is better than it was but should be 0 or - or + 1

The tempt should go to 195 degrees.
And read out 195 degrees in computer.

Confirm good hot blue spark to all plugs and good plugs.
AC delco plugs?
Make sure the dist cap and rotor iand plug wires are in good shape

Run the complete fuel pressure test and post back readings.

Clear codes and recheck for codes.
Post back any codes that come back.

What is engine vacumn readings at idle and at 2K RPM?

bozr
10-28-2009, 12:46 PM
It may not be related but I've had a NAPA cap and rotor go to random misfire in less than 2000 miles. As a test, I brushed them with Simple Green and let them soak for an hour, rinsed them off and let them dry overnight. I haven't had a singe misfire since.

I can only imagine that either the cap, rotor or both left the factory with contaminants or oil that helped propagate the carbon tracking. Whatever it was, it was a cheap fix.

donhand1
10-30-2009, 09:38 AM
Update on my jimmy I was told to pour some sea foam down the intake while it was running(boy talk about smoking),but any way I did this until it stalled.I let it set over night and when I finally got it started the next day it smoked for a while ,but still had miss fire.So to the timing again did everything by the book it is still about 8degs out,but it runs real good no miss fire at any throttle position.I'm just scared of it never know when it may come back don't know what I did to make it run this way.I did clean the gas cap,but since it missed the minute I started it I would not think this would cause it .I ran a scan on it, after clearing all codes, and driving it for a good while I get no codes and no engine light.

MT-2500
10-30-2009, 10:17 AM
Did you run the full fuel pressure and fuel pump test?
If so post back readings.
Is it still missfiring on all cylinder the same amount of missfire?
Ac delco plugs and cap and rotor?
Good hot blue spark to all plugs?

Is the dist adjustable?
Or locked solid?

Have you got the engine temp up to 195 degrees ande the computer tempt sensor reading the same 195 degrees?

Can you feel a engine miss under load?

donhand1
10-30-2009, 10:52 AM
The dist. is the locked type,no adjustment, I just got back from a good long drive with it tried to get it to miss fire but it would not.I don't see any way to check pump on dead pressure all lines are metal or hard plastic.Yes when it was missing you could feel it very much almost like running out of gas,but now it is running better than ever.The temp. is now up to 193deg this is from the scan tool.What is strange is when I put the motor in last summer it ran great for almost two months than out of the blue it started miss firing and yes all parts are delco I even went with the brass cap and rotor, not cheap.Now it does not miss at all as stated befor it has never run so good.It just make me worry will it happen again?But on the other hand I worry about everything.I whant to thank everyone for all the help and advice and will let you know when or if it comes back.I just wish I could tell someone else that is having this problem what I did,but I don't know.

MT-2500
10-30-2009, 11:41 AM
The fuel fuel pump pressure can be checked at the in line at fuel filter.
Also double check running fuel pressure after 1/2 to 1 hr driving untill good and hot.

On camshaft retart if it was 14 degrees off to start with the dist was not set right.
http://files.automotiveforums.com/gallery/showphoto.php?photo=51302

Confirm it is set right.

8-12 degrees off may be the dist gear needs to be turned 190 degrees on dist shaft.
Also on some I have slotted the hold down clamp to fine tune it.
Does the cap have room to turn another 8 degrees if clamp slotted?

Have you checked and cleaned all engine grounds?

Good hot blue spark to all plugs when engine is hot?

dr_lee29
11-04-2009, 02:49 PM
I'd love to see the solution here if you ever figure it out. I have one that acts very similarly.

MT-2500
11-04-2009, 05:00 PM
I'd love to see the solution here if you ever figure it out. I have one that acts very similarly.

Acting similarly can be a different probem.
Needs proper testing to find the problem.
There is some good information here on it .
Go threw the information and see if anything fits you problem.

If not start a New thread on yours and give all information.

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