2003 gmc envoy again…
#1
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2003 gmc envoy again…
Alright so I’ve fixed the no start issue, I’ve fixed the rpm issue, and just fixed a misfire issue. Now it decided to throw another problem my way XD… So I discovered that cylinder 4 was misfiring today and replaced the spark plug and ignition coil. It’* not misfiring anymore, hell it even runs a whole lot smoother. When I’m driving, it feels and sounds great, however when I’m at idle or in park and just sitting with it on, after about a minute or so, the engine loses power and stalls out. It starts right back up though and runs fine when driving it. It’* just stalling when sitting for a minute. So I’ve done a little digging and found that it could be a few things. Here are the things on my list to check out. Feel free to tell me I’m not in the correct ballpark.
1. fuel filter
2. mass airflow sensor
3. crankshaft position sensor
4. engine air filter
5. bad fuel in the system
6. fuel pump
do any of these things sound about right
1. fuel filter
2. mass airflow sensor
3. crankshaft position sensor
4. engine air filter
5. bad fuel in the system
6. fuel pump
do any of these things sound about right
#2
Senior Member
That'* a loaded question. What happens when it stalls? Lose spark? Fuel?
#3
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#4
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1. fuel filter <<<<<No, you'd be feeling it hesitate at driving speeds
2. mass airflow sensor <<<<<Probably not, you'd be feeling other issues, and at idle it would have the problem or not, not gradually decline
3. crankshaft position sensor <<<<<No, it probably wouldn't run, and definitely wouldn't run well
4. engine air filter <<<<<No, it'd be sluggish all the time, and at idle it would have the problem or not, not gradually decline
5. bad fuel in the system <<<<<Probably not, you'd be feeling other issues, and at idle it would have the problem or not, not gradually decline
6. fuel pump <<<<<This is my bet
2. mass airflow sensor <<<<<Probably not, you'd be feeling other issues, and at idle it would have the problem or not, not gradually decline
3. crankshaft position sensor <<<<<No, it probably wouldn't run, and definitely wouldn't run well
4. engine air filter <<<<<No, it'd be sluggish all the time, and at idle it would have the problem or not, not gradually decline
5. bad fuel in the system <<<<<Probably not, you'd be feeling other issues, and at idle it would have the problem or not, not gradually decline
6. fuel pump <<<<<This is my bet
I'd guess bad fuel pump.
1. Driving around there'* less vacuum, therefore more fuel pressure.
2. Stop and idle, vacuum goes up, fuel pressure starts to drop as fuel is consumed from the rail.
3. Unbeknownst to the driver, PCM starts to compensate for lower fuel pressure by correcting idle speed.
4. This gradual correction moves until it can be corrected no more.
5. Now the fuel pressure continues to taper off while no correction is being made.
6. Stall.
If you disconnect (and plug) the vacuum line on the fuel pressure regulator, I bet this behavior will change. If it does, we're on the right track.
#5
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Update: still having problems…
Alright so I changed the fuel filter with a brand new one and added some seafoam in the gas tank to clean any potential clogs or anything like that. After work, I was on my way home and it stalled out 3 times randomly when I was at a stop. Prior to this, I changed the spark plug and ignition coil on cylinder 4 due to a misfire. So something told me to take it to get the codes read again and it’* continuing to say “cylinder 4 misfire”. Now keep in mind, I do NOT have a check engine light that is on anymore yet I’m having this problem. Now I’ve asked some of the mechanics at the shop I work at and some of them suggested I replace the fuel injectors. I removed the spark plug from cylinder 4, and it had some black residue on the end. I’m not 100% sure if that means anything bad, but my supervisor mentioned that the injector specifically could be putting out too much gas which indicates that I need to replace the injector. I’ve cleaned the throttle body. Even changed the oil even though that doesn’t have anything to do with it. It was just time for one. Now I need to figure out what is causing it to stall at idle.
#6
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What is the fuel pressure?
#7
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ya know…..it never occurred to me that it might be the fuel injector…. I’m still having a code come up saying cylinder 4 misfire…. How likely would that be? The fuel pump is working fine by the way. Haven’t checked the fuel pressure regulator though.
#8
Senior Member
True Car Nut
[Fuel pump working fine] doesn't mean much without knowing the fuel pressure.
#9
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05-14-2020 08:23 AM