P0300 Freeze frame data
#11
12-22-2011, 08:37 AM
I've read through twice and havent seen reference to my thoughts so pardon me if the third time would have proved my ideas crap.
Maybe it's time for some old-school.
Stop off all accessory vacuum ports at manifold incl brake booster and do a low speed drive. Do vac test and leakdown for booster. If good, reconnect it and take to highway with all other vac disconnect.
- of course lean can also be from spark fail. Hows the cat efficiency?
Maybe it's time for some old-school.
The LTFT shows lean condition
Stop off all accessory vacuum ports at manifold incl brake booster and do a low speed drive. Do vac test and leakdown for booster. If good, reconnect it and take to highway with all other vac disconnect.
- of course lean can also be from spark fail. Hows the cat efficiency?
Timing
Got Timing light?
Check for jitter against marks. The position doesnt matter.. just repetition. Subjective but will show flaky CKS, or worn timing chain, or worn dist drive gear or dist bearing slop.
Check MAP against local baro with engine not running, then against vac gauge with engine running.
- other thoughts:
Wires are important. But lately I've seen overemphasis on conductivity {Ohm/foot} of wires versus jacket insulation.
Assuming GOOD quality wires to start with, I've found the primary fail is crossfiring through jacket to adjacent wire or to grd.
Already saw that on mine, and proved it by insulating and coating with silicone.. {missfire #4 but not #5, yet 4-5 touching was problem} and fits neatly with my long term empirical experience.
I dont consider that cheap.. how many on here just install new without finding why the old wires actually fail. On the few times I bothered checking conductivity was nominally good.. and ohm/range isnt as important as you might think long as it isnt grossly out.
Check for jitter against marks. The position doesnt matter.. just repetition. Subjective but will show flaky CKS, or worn timing chain, or worn dist drive gear or dist bearing slop.
Misc checks not seen
Disconnect MAF drive test. Should run better if MAF is wrong - in range. You did look for leaks in intake tube?Check MAP against local baro with engine not running, then against vac gauge with engine running.
- other thoughts:
Wires are important. But lately I've seen overemphasis on conductivity {Ohm/foot} of wires versus jacket insulation.
Assuming GOOD quality wires to start with, I've found the primary fail is crossfiring through jacket to adjacent wire or to grd.
Already saw that on mine, and proved it by insulating and coating with silicone.. {missfire #4 but not #5, yet 4-5 touching was problem} and fits neatly with my long term empirical experience.
I dont consider that cheap.. how many on here just install new without finding why the old wires actually fail. On the few times I bothered checking conductivity was nominally good.. and ohm/range isnt as important as you might think long as it isnt grossly out.
#12
12-22-2011, 06:59 PM
Well. I put new plug wires on and as I expected its not the solution. now i'm 98% sure its getting good consistent blue spark.
So you guys think the lean condition on bank 1 would be my bad o2?
Question, shouldn't it be a rich condition? Cylinders 1 & 4 are the ones misfiring under load. I'm guessing that should be causing un-burnt fuel. Even the engine light flashes going uphill so it is rich
I have no timing light but the cam retard reading stays the same doesn't bounce around is that as good as a timing light
Tried the maf disconnect route Still misfired
Map works via ethos at idle is 32 or something and it jumps up when revved
Im at a loss Parts store is open for an hour so any last suggestions before i just sell my 4 cylinder blazer that idles with 6
So you guys think the lean condition on bank 1 would be my bad o2?
Question, shouldn't it be a rich condition? Cylinders 1 & 4 are the ones misfiring under load. I'm guessing that should be causing un-burnt fuel. Even the engine light flashes going uphill so it is rich
I have no timing light but the cam retard reading stays the same doesn't bounce around is that as good as a timing light
Tried the maf disconnect route Still misfired
Map works via ethos at idle is 32 or something and it jumps up when revved
Im at a loss Parts store is open for an hour so any last suggestions before i just sell my 4 cylinder blazer that idles with 6
#14
12-22-2011, 09:41 PM
so its not the o2s? they are messengers to the pcm no?
so is it mechanical? valves? or is it Spark? Ecm Icm
The car idles fine except slight surging, But no constant miss
Under load 1 and 4 miss with the occasional random cylinder.
Could it be the intake gasket? I thought usually it was cylinder 6
It ran so good before...
so is it mechanical? valves? or is it Spark? Ecm Icm
The car idles fine except slight surging, But no constant miss
Under load 1 and 4 miss with the occasional random cylinder.
Could it be the intake gasket? I thought usually it was cylinder 6
It ran so good before...
#15
12-23-2011, 10:29 AM
I had a whole big post on your MAP reading. Coupled with a geezer brain fart.
You might doublecheck to make sure that MAP reading is in absolute pressure - which I believe it is - Or if it's differential pressure versus atmosphere.
- If readout is about 100 kPa, key on engine off, it's absolute. If it's 0, it's differential.
If it's absolute pressure, then your manifold vacuum is good.
Differential.. then it's bad.
Bothersome: The spikes probably reflect the cylinder misses. So which way is 'up'?
You might doublecheck to make sure that MAP reading is in absolute pressure - which I believe it is - Or if it's differential pressure versus atmosphere.
- If readout is about 100 kPa, key on engine off, it's absolute. If it's 0, it's differential.
If it's absolute pressure, then your manifold vacuum is good.
Differential.. then it's bad.
Bothersome: The spikes probably reflect the cylinder misses. So which way is 'up'?
#16
12-23-2011, 05:25 PM
It reads 99 with key on engine off. So i don't have a vacuum leak?
Or the sensor isn't bad?
Or the sensor isn't bad?
#17
12-23-2011, 07:36 PM
That means that's probably good manifold vacuum.
Note that, with a vacuum gauge, good vacuum in inches/hg is about 2/3 barometer or 18-22 in/hg.
99 minus 36 = 63 kPa or 18.6 inHg vacuum
So yes, Your problem looks like either spark or fuel.
I WOULD like to understand better those spikes in the map readout. They would appear to be spikes in vacuum. ie; less pressure - more vacuum
Note that, with a vacuum gauge, good vacuum in inches/hg is about 2/3 barometer or 18-22 in/hg.
99 minus 36 = 63 kPa or 18.6 inHg vacuum
So yes, Your problem looks like either spark or fuel.
I WOULD like to understand better those spikes in the map readout. They would appear to be spikes in vacuum. ie; less pressure - more vacuum
#19
12-25-2011, 06:45 AM
I'm not sure if I can help. But I do have a couple of questions that may help us help you.
You cite the problem as P0300 code. How often is it set (amount of driving before it sets after clearing the code)? Does it set at idle or after driving the vehicle?
Do you have driveability problems or is the problem only at idle? You said "Now i can hear something on the drivers side of the motor maybe that sounds like air is rushing through? It seems to affect the idle alot. But its most noticeable when the engine bogs after revving, it seems to hesitate when revving in neutral."
Did you test the timing light like pettyfog suggested? What were the results of that testing?
Have you done a compression test on all cylinders? What were each cylinders values? And check the gap on each spark plug and make sure it is correct while you have them out for the compression test
You cite the problem as P0300 code. How often is it set (amount of driving before it sets after clearing the code)? Does it set at idle or after driving the vehicle?
Do you have driveability problems or is the problem only at idle? You said "Now i can hear something on the drivers side of the motor maybe that sounds like air is rushing through? It seems to affect the idle alot. But its most noticeable when the engine bogs after revving, it seems to hesitate when revving in neutral."
Did you test the timing light like pettyfog suggested? What were the results of that testing?
Have you done a compression test on all cylinders? What were each cylinders values? And check the gap on each spark plug and make sure it is correct while you have them out for the compression test
Last edited by kevinph; 12-25-2011 at 06:50 AM. Reason: change leakdown to compression
#20
12-25-2011, 09:58 AM
Just some random thoughts....
If the SES light is blinking, it's indicating a misfire. P0300 series DTC's are almost always caused by secondary ignition faults, although low fuel pressure* can also set them. You've replaced all of the secondary ignition parts, with the exception of the ignition coil; one thing you need to keep in mind is that these engines are very fussy when it comes to secondary ignition parts. What brand of parts did you use? They really like AC Delco and anything else could be causing the problem. Camshaft retard at -7 is not within spec but, it's not the problem, guaranteed. When asked about your distributor shaft play, you said, "It hardly moves side to side". There should be zero radial movement! Pettyfog mentioned checking timing with a light; doing that would give you an indication if timing is jumping around, but an oscilloscope would show actual distributor shaft bushing wear. Unfortunately most people don't have a scope. As mentioned, these distributors, and the bushings, are pretty cheezy to say the least, and they have a very high failure rate. Dorman makes a replacement distributor with an all aluminum housing for around $100, good stuff.
* Key ON, engine OFF, fuel pump running, pressure must be 60psi to 66psi and must remain above 55psi for 10 minutes after the pump shuts off. GM does not publish engine running fuel pressure specs.
If the SES light is blinking, it's indicating a misfire. P0300 series DTC's are almost always caused by secondary ignition faults, although low fuel pressure* can also set them. You've replaced all of the secondary ignition parts, with the exception of the ignition coil; one thing you need to keep in mind is that these engines are very fussy when it comes to secondary ignition parts. What brand of parts did you use? They really like AC Delco and anything else could be causing the problem. Camshaft retard at -7 is not within spec but, it's not the problem, guaranteed. When asked about your distributor shaft play, you said, "It hardly moves side to side". There should be zero radial movement! Pettyfog mentioned checking timing with a light; doing that would give you an indication if timing is jumping around, but an oscilloscope would show actual distributor shaft bushing wear. Unfortunately most people don't have a scope. As mentioned, these distributors, and the bushings, are pretty cheezy to say the least, and they have a very high failure rate. Dorman makes a replacement distributor with an all aluminum housing for around $100, good stuff.
* Key ON, engine OFF, fuel pump running, pressure must be 60psi to 66psi and must remain above 55psi for 10 minutes after the pump shuts off. GM does not publish engine running fuel pressure specs.
Thread
Thread Starter
Forum
Replies
Last Post
toploader9
2nd Generation S-series (1995-2005) Tech
3
08-19-2015 01:09 PM
Chevy33
2nd Generation S-series (1995-2005) Tech
7
08-08-2014 07:42 PM
