Help.. Engine stumble... help!
Thread Starter
Le Mans Master
Joined: Nov 2002
Posts: 7,080
Likes: 0
From: Corvette valley Georgia
St. Jude Donor '06
Help.. Engine stumble... help!
I have a engine stumble that driving me nuts, it happens in OD @65 or so 1800RPM , when you depress the throttle slightly the engine will stumble till the trans down shift and it clears untill the trans upshifts and gets back to the same senario and load.
I have replaced the following:
1 Injectors
2 fuel filter
3 plugs and wires
4 air filter
The car runs hard @ WOT and pulls hard thru the RPM range.
I have scaned the engine it and has no codes.
The only thing is the O2 sensors are a little erratic thru the scan time( no codes)
Are the O2 sensors going bad? causing the stumble or is it somthing else?
TIA :confused: Oh yeah it has 113000 miles on it!! and it a 92 speed density system
[Modified by grapeknutz, 6:29 PM 12/1/2003]
[Modified by grapeknutz, 12:14 PM 12/2/2003]
I have replaced the following:
1 Injectors
2 fuel filter
3 plugs and wires
4 air filter
The car runs hard @ WOT and pulls hard thru the RPM range.
I have scaned the engine it and has no codes.
The only thing is the O2 sensors are a little erratic thru the scan time( no codes)
Are the O2 sensors going bad? causing the stumble or is it somthing else?
TIA :confused: Oh yeah it has 113000 miles on it!! and it a 92 speed density system
[Modified by grapeknutz, 6:29 PM 12/1/2003]
[Modified by grapeknutz, 12:14 PM 12/2/2003]
Safety Car
Joined: Feb 2002
Posts: 4,212
Likes: 10
From: Sun City West Az
Re: Help.. Engine stumble... help! (grapeknutz)
I see you have a speed/density car. My first thought is the TPS and then the MAP. Since your TPS isn't adjustable, you might want to put a scanner on the ALDL and watch the TPS voltage by cracking the the throttle with the key on engine off. It should go SMOOTHLY from .3-.9v (closed throttle) to 4.5+ v @WOT with no hick-ups.
Thread Starter
Le Mans Master
Joined: Nov 2002
Posts: 7,080
Likes: 0
From: Corvette valley Georgia
St. Jude Donor '06
Re: Help.. Engine stumble... help! (ittlfly)
I see you have a speed/density car. My first thought is the TPS and then the MAP. Since your TPS isn't adjustable, you might want to put a scanner on the ALDL and watch the TPS voltage by cracking the the throttle with the key on engine off. It should go SMOOTHLY from .3-.9v (closed throttle) to 4.5+ v @WOT with no hick-ups.
The voltage is 0.73 at idle to 4.0 at WOT looks good here!
Safety Car
Joined: Feb 2002
Posts: 4,212
Likes: 10
From: Sun City West Az
Re: Help.. Engine stumble... help! (grapeknutz)
I assume that it was a smooth transmission through the TPS numbers. If that's ok you could check the MAP sensor for proper voltage. If you have a Helms, the procedure is in book 2 chart C-1D.. ..the voltage should be about 1-2 v @ idle and increase to 4-4.8 v @ WOT. You can also check it with a vacuum pump and a DVM.
[Modified by ittlfly, 6:16 PM 12/1/2003]
[Modified by ittlfly, 6:16 PM 12/1/2003]
Thread Starter
Le Mans Master
Joined: Nov 2002
Posts: 7,080
Likes: 0
From: Corvette valley Georgia
St. Jude Donor '06
Re: Help.. Engine stumble... help! (ittlfly)
I didnt even think about the MAP sensor, I will get a vacume pump and test that and get back to you what I find!
Pro
Joined: Apr 2001
Posts: 744
Likes: 13
From: Lenoir City TN
Re: Help.. Engine stumble... help! (grapeknutz)
Please let me know if it turns out to be the MAP sensor. I have a speed density 91 L-98 motor that has a stumble around 1200 rpms or so, just off idle, clear above and below. I already changed the TPS, no help. Mine does it worse when it is still cold, gets better when its hot.
Thanks
Thanks
Thread Starter
Le Mans Master
Joined: Nov 2002
Posts: 7,080
Likes: 0
From: Corvette valley Georgia
St. Jude Donor '06
Re: Help.. Engine stumble... help! (cshuman)
OK I replaced the MAP sensor and I still have the stumble.
The stumble happens when the car is warm. Anybody have an idea to this problem? :confused:
The stumble happens when the car is warm. Anybody have an idea to this problem? :confused:
Melting Slicks
Joined: May 2001
Posts: 2,143
Likes: 7
From: San Diego CA
Re: Help.. Engine stumble... help! (grapeknutz)
You may have initial stages of Opti failure. Next stage is a stumble at idle. Third stage is both will get worse.
You'll probably never see a code.
Check the water pump weep hole for green stuff. There shouldn't be any. If the pump is starting to go, you might be seeing a line of dried coolant on the underside of the hood above the surpentine belt.
Just noticed you last post. Mine got worse as the temps got hot.
[Modified by John Row, 10:24 AM 12/2/2003]
You'll probably never see a code.
Check the water pump weep hole for green stuff. There shouldn't be any. If the pump is starting to go, you might be seeing a line of dried coolant on the underside of the hood above the surpentine belt.
Just noticed you last post. Mine got worse as the temps got hot.
[Modified by John Row, 10:24 AM 12/2/2003]
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Safety Car
Joined: Feb 2002
Posts: 4,212
Likes: 10
From: Sun City West Az
Re: Help.. Engine stumble... help! (John Row)
I agree with John. I was just suggesting to check the TPS and MAP to see if their output responded correctly to the voltage and vacuum changes. I assume the MAP didn't check out ok and that's why you replaced it. Unfortunetly your opti may be on its way out.. Before you jump in and replace it, take a look at the coil and coil driver for correct output. Sometimes it / they will start to crap out under load. However, "when you depress the throttle slightly" doesn't exactly qualify as heavy load. :lol:
