96' Blazer with hesitation and misfires
Thread Starter
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Starting Member
Joined: May 2016
Posts: 200
Alrighty, I'm back!
So from the way it pressure tested awhile back and assuming that the fuel pump was probably low quality, I decided to tear into it.
Well, the pump was an Airtex e3925m but the center hose was pushed on without the locking clip. Next, the tank vent valve had been broke off and they had siliconed the crap out of it trying to get it to seal. I'm ordering an ACdelco 1735 pump, new clips and a new vent valve for the tank.
That seems to be enough to cause a miss or stumble.
We will see soon enough..
Later
So from the way it pressure tested awhile back and assuming that the fuel pump was probably low quality, I decided to tear into it.
Well, the pump was an Airtex e3925m but the center hose was pushed on without the locking clip. Next, the tank vent valve had been broke off and they had siliconed the crap out of it trying to get it to seal. I'm ordering an ACdelco 1735 pump, new clips and a new vent valve for the tank.
That seems to be enough to cause a miss or stumble.
We will see soon enough..
Later
Moderator
Joined: Oct 2014
Posts: 4,336
From: North Central Indiana
Alrighty, I'm back!
So from the way it pressure tested awhile back and assuming that the fuel pump was probably low quality, I decided to tear into it.
Well, the pump was an Airtex e3925m but the center hose was pushed on without the locking clip. Next, the tank vent valve had been broke off and they had siliconed the crap out of it trying to get it to seal. I'm ordering an ACdelco 1735 pump, new clips and a new vent valve for the tank.
That seems to be enough to cause a miss or stumble.
We will see soon enough..
Later
So from the way it pressure tested awhile back and assuming that the fuel pump was probably low quality, I decided to tear into it.
Well, the pump was an Airtex e3925m but the center hose was pushed on without the locking clip. Next, the tank vent valve had been broke off and they had siliconed the crap out of it trying to get it to seal. I'm ordering an ACdelco 1735 pump, new clips and a new vent valve for the tank.
That seems to be enough to cause a miss or stumble.
We will see soon enough..
Later
Thread Starter
|
Starting Member
Joined: May 2016
Posts: 200
Well, I'm back...lol. What a summer this has been. So here's an update...
Replaced the fuel pump assembly with an ACdelco unit. Also, when the previous mechanic replaced the pump, he broke the vent valve on the front end of the tank.
I'm reasonably sure of this by the golf ball sized glob of silicon over the vent and hose.
So, I replaced that too plus new vent line.
The previous fuel pump was also missing the center line lock. I replaced all three with new clips.
This all corrected the stutter or starving of fuel but I still have some kind of a ignition bump. When I say "bump" I mean something not smooth in the way it runs.
I also cleaned the egr valve and the mass airflow sensor. This also helped some.
Next, I was looking at the engine and noticed it had Autolite plugs.
To be fair, they were double platinum and the correct one for my engine but...
Anyway, I replaced them with Iridium ACdelco plugs. That made the biggest difference so far after the fuel pump replacement.
I also replaced the coil, 25 bucks...why not..lol
The "bump" almost feels like I have fire jumping from the wires or something.
I've been planning on mounting my gopro under the hood to see if there is fire jumping around. Haven't got that done yet.
Well, that's about it
Later
Replaced the fuel pump assembly with an ACdelco unit. Also, when the previous mechanic replaced the pump, he broke the vent valve on the front end of the tank.
I'm reasonably sure of this by the golf ball sized glob of silicon over the vent and hose.
So, I replaced that too plus new vent line.
The previous fuel pump was also missing the center line lock. I replaced all three with new clips.
This all corrected the stutter or starving of fuel but I still have some kind of a ignition bump. When I say "bump" I mean something not smooth in the way it runs.
I also cleaned the egr valve and the mass airflow sensor. This also helped some.
Next, I was looking at the engine and noticed it had Autolite plugs.
To be fair, they were double platinum and the correct one for my engine but...
Anyway, I replaced them with Iridium ACdelco plugs. That made the biggest difference so far after the fuel pump replacement.
I also replaced the coil, 25 bucks...why not..lol
The "bump" almost feels like I have fire jumping from the wires or something.
I've been planning on mounting my gopro under the hood to see if there is fire jumping around. Haven't got that done yet.
Well, that's about it
Later
Moderator
Joined: Oct 2014
Posts: 4,336
From: North Central Indiana
How about your name so I don't have to call you Graveyard anymore!
So I went back and re-read your posts since last May on your performance problems. I can safely say that you have made it through almost all the common causes of misfires. You have new Delco cap/rotor and cam retard is set to 0, new Delco Iridium spark plugs and fuel pump is new AC Delco. Fuel pressure regulator is at normal pressure, and injectors are not leaking down pressure over 10 minutes after energizing fuel pump. Sounds like only problem is a rough idle, and vehicle runs well other than that. No SES lights have been on.
Fuel system testing is complete, so lets complete the verification of common ignition system problems. Test/inspect your plug wires. Inspect inside of each of the 14 boots with a flashlight for carbon tracking or corrosion. Terminals should be shiny and clean. The length of the wire should be clean and not burned anywhere. Test the resistance of each wire with an ohm meter. Should be about 1200-1500ohms per foot of length. I'm going to assume they are OK - but they should be checked.
Now I'm going to tell you about a screw-up I made on my own vehicle when putting the engine back in. I failed to route the wiring from the PCM across the top of the engine correctly and ended up with the harness laying aganst the tubes to the A.I.R. system in front of the passenger exhaust manifold. After a while, the hot tube to the AIR check valve burned through the plastic harness protector and then the wiring insulator to one of the injectors. Eventually it got bad enough it grounded enough to set a SES code, but performance was funky for quite some time. You may want to check this since you had the intake off, and make sure your wiring is routed away from the hot exhaust parts and undamaged. I blamed a trans rebuild for harsh TCC and shifting funny, when it was really an engine performance problem. Fixed the injector wire and trans is smooth as silk.
If you still have your rough idle, lets dig the Dash Command back out. If a miss is bad enough to feel, I'm quite certain the misfire detection would pick it up. Whether or not it would set a code and turn on the light depends on the severity and frequency of the miss - but it should count even 1 misfire in a so-many-second time period and display it in Dash Command in the misfire counters you previously configured. If you see absolutely no misses, then pull a plug wire and make sure it can detect that miss correctly.
Another thing you can do is to eliminate vibrations from all accessories. Just take the serpentine belt off and see if the roughness goes away.
Please try these things and let us know what you find. We can go from there.
Best regards,
Les
So I went back and re-read your posts since last May on your performance problems. I can safely say that you have made it through almost all the common causes of misfires. You have new Delco cap/rotor and cam retard is set to 0, new Delco Iridium spark plugs and fuel pump is new AC Delco. Fuel pressure regulator is at normal pressure, and injectors are not leaking down pressure over 10 minutes after energizing fuel pump. Sounds like only problem is a rough idle, and vehicle runs well other than that. No SES lights have been on.
Fuel system testing is complete, so lets complete the verification of common ignition system problems. Test/inspect your plug wires. Inspect inside of each of the 14 boots with a flashlight for carbon tracking or corrosion. Terminals should be shiny and clean. The length of the wire should be clean and not burned anywhere. Test the resistance of each wire with an ohm meter. Should be about 1200-1500ohms per foot of length. I'm going to assume they are OK - but they should be checked.
Now I'm going to tell you about a screw-up I made on my own vehicle when putting the engine back in. I failed to route the wiring from the PCM across the top of the engine correctly and ended up with the harness laying aganst the tubes to the A.I.R. system in front of the passenger exhaust manifold. After a while, the hot tube to the AIR check valve burned through the plastic harness protector and then the wiring insulator to one of the injectors. Eventually it got bad enough it grounded enough to set a SES code, but performance was funky for quite some time. You may want to check this since you had the intake off, and make sure your wiring is routed away from the hot exhaust parts and undamaged. I blamed a trans rebuild for harsh TCC and shifting funny, when it was really an engine performance problem. Fixed the injector wire and trans is smooth as silk.
If you still have your rough idle, lets dig the Dash Command back out. If a miss is bad enough to feel, I'm quite certain the misfire detection would pick it up. Whether or not it would set a code and turn on the light depends on the severity and frequency of the miss - but it should count even 1 misfire in a so-many-second time period and display it in Dash Command in the misfire counters you previously configured. If you see absolutely no misses, then pull a plug wire and make sure it can detect that miss correctly.
Another thing you can do is to eliminate vibrations from all accessories. Just take the serpentine belt off and see if the roughness goes away.
Please try these things and let us know what you find. We can go from there.
Best regards,
Les
Thread Starter
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Starting Member
Joined: May 2016
Posts: 200
Okay Les, My Name is Greg Graves.
As far as just checking at night, I seem to notice it after it warms up. So I felt I would just record it on the way to work.
It's okay to drive but I'm not satisfied with the performance yet, or rather the consistence of the rpm at highway speeds.
I really like the little truck or I wouldn't be putting this much work and cash into it.
But I am ready to find the solution...lol
Thanks Guys
As far as just checking at night, I seem to notice it after it warms up. So I felt I would just record it on the way to work.
It's okay to drive but I'm not satisfied with the performance yet, or rather the consistence of the rpm at highway speeds.
I really like the little truck or I wouldn't be putting this much work and cash into it.
But I am ready to find the solution...lol
Thanks Guys
Moderator
Joined: Oct 2014
Posts: 4,336
From: North Central Indiana
Hi Greg,
I've been thinking the performance problem you have is only a rough idle as you described in post#14 of your original thread on setting timing. But I see that since you set CMP retard the issue has changed to an occasional misfire at highway speeds as described in post #17 of this thread. I also see that the vehicle died once and would not restart until you had coasted to a stop (post #23 of this thread). Since that time you have replaced the fuel pump and ignition coil and spark plugs and misfire or roughness at highway speed is still there all of the time. Is this correct? Can you add any further description?
I still think watching the misfire counters when you feel the problem would be a useful thing to do. See if a misfire happens on any particular cylinder. Also you could set up short term fuel trim gauges (use needles not digital readout because they swing pretty rapidly) and see if anything is going lean or rich when misfire happens (I wouldn't monitor misfire counters at same time due to bandwidth required). Short term fuel trims monitored by themselves at a decent bandwidth should swing back and forth across zero. If the average is skewed high or low, then system is trying to either add fuel or take away fuel from the factory calibration based on O2 sensor readings. If they are both swinging back and forth across zero when the misfire occurs, then fuel mix is not the cause of your misfire and I think you could forget about your fuel system, vacuum leaks, EGR, and O2 sensors and look elsewhere.
Last thing I want to mention is that if the problem is happening at about 45-50 mph, quite often rough TCC engagement/disengagement can be mistaken as a misfire.
I've been thinking the performance problem you have is only a rough idle as you described in post#14 of your original thread on setting timing. But I see that since you set CMP retard the issue has changed to an occasional misfire at highway speeds as described in post #17 of this thread. I also see that the vehicle died once and would not restart until you had coasted to a stop (post #23 of this thread). Since that time you have replaced the fuel pump and ignition coil and spark plugs and misfire or roughness at highway speed is still there all of the time. Is this correct? Can you add any further description?
I still think watching the misfire counters when you feel the problem would be a useful thing to do. See if a misfire happens on any particular cylinder. Also you could set up short term fuel trim gauges (use needles not digital readout because they swing pretty rapidly) and see if anything is going lean or rich when misfire happens (I wouldn't monitor misfire counters at same time due to bandwidth required). Short term fuel trims monitored by themselves at a decent bandwidth should swing back and forth across zero. If the average is skewed high or low, then system is trying to either add fuel or take away fuel from the factory calibration based on O2 sensor readings. If they are both swinging back and forth across zero when the misfire occurs, then fuel mix is not the cause of your misfire and I think you could forget about your fuel system, vacuum leaks, EGR, and O2 sensors and look elsewhere.
Last thing I want to mention is that if the problem is happening at about 45-50 mph, quite often rough TCC engagement/disengagement can be mistaken as a misfire.
Last edited by LesMyer; Sep 21, 2016 at 08:19 AM.
Moderator
Joined: Oct 2014
Posts: 4,336
From: North Central Indiana
That's the Torque Converter Clutch engagement. In 4th gear should start trying to lock up at 45 mph cruise. Makes a few hundred difference in RPM. Sometimes seeing the RPMs drop and then go back up from TCC engagement/disengagement can be mistaken as a problem.
