Stumbling in high rpms...only at WOT
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Joined: Jul 2004
Posts: 141
Stumbling in high rpms...only at WOT
To start things off my car only has 62k on it. I know that doesn't mean things cant go wrong but I wasn't prepared for them to start.
Anyway, lately my car has been cutting out at high rpms when going WOT. It wont do it every time, but when it does it, it makes a loud pop out of my cutout. Also when in neutral and I rev it up by going WOT it will cut out a few times when the rpms get a little past 4k. It usually does this every time. If I bring the rpms up without going WOT the car runs fine. What would cause it to do it only under WOT? Everything else is fine too, the car idles fine, drives fine in all other conditions, only at WOT in the upper rpms am I noticing this problem. Thanks for your help.
Andy
Anyway, lately my car has been cutting out at high rpms when going WOT. It wont do it every time, but when it does it, it makes a loud pop out of my cutout. Also when in neutral and I rev it up by going WOT it will cut out a few times when the rpms get a little past 4k. It usually does this every time. If I bring the rpms up without going WOT the car runs fine. What would cause it to do it only under WOT? Everything else is fine too, the car idles fine, drives fine in all other conditions, only at WOT in the upper rpms am I noticing this problem. Thanks for your help.
Andy
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Joined: Oct 2006
Posts: 2,728
From: Post Falls, Idaho
My car does the exact samething. I lived with it for 4 months and finally bought a fuel pressure gauge. When i really get on it the fuel pressure will drop to 0 for a split second. This is so common that there are 20+ things it could be. Does it do it when it is cold? This problem usually does not happen until the car is real warm. Fuel filter been changed lately? They this first. It's real easy and cheap. Also any codes? Then we will go from there.
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Joined: Jul 2004
Posts: 141
Thanks for the reply. I never get on it when the engine is cold so I am not sure if it does it then. Fuel filter has not been changed either. The check engine light will come on every now and then but that hasn't come on since the car has been acting up. It's just so strange that it doesn't do it all the time. Like I said though, when in neutral and I rev it up by going WOT it will cut out and pop almost every time and usually do it a couple of times between about 4k and red line.
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Joined: Aug 2005
Posts: 4,405
From: Kantuckee Yo'
Mine had a very slight stumble around 5.5K RPM, it was very intermittant. Somene recently posted the exact same problem and found the screw holding the opti rotor on had backed out.
Right now I am pulling my engine and I found both screw halfway backed out and the only thinh retaining the rotor is the springy terminal on top. To me it sounds like ignition.
Rule out the fuel then start checking the opti.
Right now I am pulling my engine and I found both screw halfway backed out and the only thinh retaining the rotor is the springy terminal on top. To me it sounds like ignition.
Rule out the fuel then start checking the opti.
Thread Starter
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Joined: Jul 2004
Posts: 141
Mine had a very slight stumble around 5.5K RPM, it was very intermittant. Somene recently posted the exact same problem and found the screw holding the opti rotor on had backed out.
Right now I am pulling my engine and I found both screw halfway backed out and the only thinh retaining the rotor is the springy terminal on top. To me it sounds like ignition.
Rule out the fuel then start checking the opti.
Right now I am pulling my engine and I found both screw halfway backed out and the only thinh retaining the rotor is the springy terminal on top. To me it sounds like ignition.
Rule out the fuel then start checking the opti.
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Joined: Oct 2006
Posts: 19
From: georgetown ky
my 94 did same thing very bad when hitting 150 shot of nos any how changed plugs wires nothing helped then i decided to change cap and rotor
and found that my opti was full of rust (thanks to the guy who sold it to me)
I only have 80k on mine so its not unheard of for low miles, new opti later
no stumble above 4k. changing it wasn't that bad about 3 hours total.
and found that my opti was full of rust (thanks to the guy who sold it to me)
I only have 80k on mine so its not unheard of for low miles, new opti later
no stumble above 4k. changing it wasn't that bad about 3 hours total.
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Joined: Mar 2004
Posts: 147
True. Check the simple things first. Have you verified spark at each plug? A tester is ~$3 at most local autoparts stores. With the cheap ones all you have to do is plug it into each ignition wire, clamp onto a ground, and watch for a blue spark while someone else turns the key to crank. AT LEAST do this test before you start attempting to take apart your distributor.
Also, if you feel that you are "not too savvy" when it comes to these cars but you plan on keeping yours, the investment in a shop manual is well worth it.
http://www.helminc.com/helm/product2...WERSEQU7P16DN4
Good luck & let us know
Also, if you feel that you are "not too savvy" when it comes to these cars but you plan on keeping yours, the investment in a shop manual is well worth it.
http://www.helminc.com/helm/product2...WERSEQU7P16DN4
Good luck & let us know
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Joined: Jul 2004
Posts: 141
I still haven't figured this out yet. Someone mentioned to try changing the wire from the harness to the opti. How hard is this to get to and where exactly is it? Also can I get it at any auto parts store or do I have to buy all new wires?
also, is this what I'm looking for?
http://cgi.ebay.com/ebaymotors/LT1-O...spagenameZWDVW
also, is this what I'm looking for?
http://cgi.ebay.com/ebaymotors/LT1-O...spagenameZWDVW
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Joined: Mar 2004
Posts: 147
Shoebox's OPTI and Spark Test
The opti has two functions in the spark process. The first thing that happens is as the cam turns, the optical section of the optispark picks up the signals by the rotation of the shutter wheel. The pulses are sent to the PCM via the optispark electrical harness. The PCM processes the signals along with other sensor input and determines the proper time for the coil to fire. The PCM sends a signal to the Ignition Control Module (ICM) and it, in turn, causes the coil to fire. The spark from the coil travels through the coil wire back to the secondary ignition section of the optispark (cap and rotor), to be distributed to the proper cylinder.
If the opti is never sending the signal to the PCM, the PCM will never send a signal to fire the coil.
Here is some testing you can do. Refer to this diagram.
Disconnect the ICM connector. Leave coil connected.
Turn key to ON.
Check for dc voltage with a digital meter at harness terminal "A" to ground and and also "D" to ground. Note: Use a high impedance meter (at least 10 megohm) when dealing with the PCM.
Result should be 10v dc or more on both terminals. If you get no voltage, use the diagram and chase back toward the coil and the ignition fuse. Power for the ICM comes from the ignition fuse and through the coil, so any of that could be bad.
If you have good voltage, switch the meter to ac scale and connect test leads to terminal "B" and to ground. Observe meter while cranking the engine. You should see between 1 and 4 volts ac (those are the pulses that trigger the coil to fire).
If you don't see the proper ac voltage the problem could be the optispark, the harness to the optispark, the PCM or any of the wiring in between. Visually inspect all the connections you can get to for poor contact or corrosion.
edited 5/16/2004
The opti has two functions in the spark process. The first thing that happens is as the cam turns, the optical section of the optispark picks up the signals by the rotation of the shutter wheel. The pulses are sent to the PCM via the optispark electrical harness. The PCM processes the signals along with other sensor input and determines the proper time for the coil to fire. The PCM sends a signal to the Ignition Control Module (ICM) and it, in turn, causes the coil to fire. The spark from the coil travels through the coil wire back to the secondary ignition section of the optispark (cap and rotor), to be distributed to the proper cylinder.
If the opti is never sending the signal to the PCM, the PCM will never send a signal to fire the coil.
Here is some testing you can do. Refer to this diagram.
Disconnect the ICM connector. Leave coil connected.
Turn key to ON.
Check for dc voltage with a digital meter at harness terminal "A" to ground and and also "D" to ground. Note: Use a high impedance meter (at least 10 megohm) when dealing with the PCM.
Result should be 10v dc or more on both terminals. If you get no voltage, use the diagram and chase back toward the coil and the ignition fuse. Power for the ICM comes from the ignition fuse and through the coil, so any of that could be bad.
If you have good voltage, switch the meter to ac scale and connect test leads to terminal "B" and to ground. Observe meter while cranking the engine. You should see between 1 and 4 volts ac (those are the pulses that trigger the coil to fire).
If you don't see the proper ac voltage the problem could be the optispark, the harness to the optispark, the PCM or any of the wiring in between. Visually inspect all the connections you can get to for poor contact or corrosion.
edited 5/16/2004
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