minor engine stumble issue. December 12, 2012, 10:07:08 PM 87 5.0 w/aod 20th anniv cougsymptom: engine feels like its missing under steady applied throttle.~only during drive conditions if i apply just a tiny bit of throttle and **allow the transmission** to accelerate my car, there happens to be a feel of a miss as the engine is pulling me down the road.I do not press in further or let off the gas, my foot stays in one spot. I let the transmission run through its first to second, then second to third gear but somewhere during this low RPM acceleration event , the engine shudder happens **nearly all the time**.this is a new event that showed up about a month ago.What i did:~i shot gunned the problem at first by tuning up with wires, plugs, cap rotor, fuel filter and additionally i installed a new TPS. These things needed done anyway.Problem remained after basic tune up.~KOEO - pulled codes and have 34 only in KOEO & ~KOER - on demand = code 34. Memory= 34 & 29I recenly replaced the heater core and remove the PCV screen, replace some vac lines that were in bad shape, installed everything back to correct order and the problem still remains.I do not know how to temporarily defeat the EGR solenoid in an appropriate manner in order to clear the code and simulate vac to the egr, so i am wondering if the "lack of" the egr opening at all would cause an engine shudder.The problem is non existent in most higher speeds and / or random acceleration / deceleration events.it only shows up when i am driving like a civilized human being simply chuggin along cool calm and collected letting the car pull me along. If i simply put my foot on the pedal a little bit to get me going, let the transmission bring me up to ever so slow increasing speed, at some point the engine shutters and i dont know why. this symptom caused me to randomly drop in a TPS thinking there may be a minor flat spot on the element inside which which was F'ign with the eec. .... not the case apparently. Quote Selected
minor engine stumble issue. Reply #1 – December 12, 2012, 10:14:41 PM no i did not check for fuel moisture in the FPR vac line,, forgot to.No i have not check my fuel pres yet, can do tomorrow but i would rather have the hose extender so i can read it through my windshield while driving down the road to verify fuel pres while under a load.spark is whitish blue.fuel injector screens are OEMFPR is likely OEM as well.,, donocan do compression test as well. Quote Selected
minor engine stumble issue. Reply #2 – December 12, 2012, 11:22:58 PM The EGR could cause this. If it's not operating properly exhaust gas can enter the combustion chamber and cause the stumble. If you unplug the EGR the computer should ignore it and operate the engine sans exhaust gas. This is unless the EGR valve is stuck slightly open, than unplugging it won't help. If the stumble goes away it's probably the EGR valve. I would also check the FP regulator just to be on the safe side. Quote Selected
minor engine stumble issue. Reply #3 – December 13, 2012, 12:37:57 AM sorry, forgot to add, i pulled vac on the egr and it holds very well.I do not know if there is carbon build up on its seat preventing it from seating properly.what i do know is,,,,,,,,, i confirmed the code because when i removed the egr solenoid, applied power, i was not able to confirm there would be air flow through the vac fitting paths. I measured the resistance of the egr solenoid and got nearly a short, much lower resistance than expected , opened it up and found a diode across the top of the solenoid windings to be shorted. As a test only i cut one side of the diode to remove the dead short and found perfect resistance. I re-energized the solenoid but i do not believe its moving enough to allow a vac path which would ultimately end up at the egr.i will check the egr seat tomorrow, i should do some PM on that anyway. Quote Selected
minor engine stumble issue. Reply #4 – December 13, 2012, 11:58:27 PM fuel pres is 36 with vac line disconnected and plugged.Fuel pres is 42 with vac line on.no fuel found in the fuel pres vac hose,, i grounded the tan light green wire at the eec conn to manually make the fuel pump run full time for testing.KOER, fuel pres held steady at the same psi as when the car was not running.Vac pres on the vac tree was a steady 18psi at idle. Quote Selected
minor engine stumble issue. Reply #5 – December 14, 2012, 01:56:04 AM Quote from: jcassity;404475sorry, forgot to add, i pulled vac on the egr and it holds very well.I do not know if there is carbon build up on its seat preventing it from seating properly.what i do know is,,,,,,,,, i confirmed the code because when i removed the egr solenoid, applied power, i was not able to confirm there would be air flow through the vac fitting paths.There is a sometimes useful tool for checking solenoids. It's called the Output State Check. When KOEO finishes outputing codes it is setup for doing the output check. Each time the throttle is pushed to WOT it changes the state of the solenoids, Off to On, On to Off etc Quote Selected
minor engine stumble issue. Reply #7 – December 14, 2012, 09:56:13 AM yep, your right, posted it bass akwards, sorry.i really dont care if the EGR solenoid is the cause, i would like a way to defeat the code to see if i can make the symtom go away. I suppose i can just push a little harder on the gas pedal. I was hunting down another solenoid like it in the car to borrow and use it in the egr line up. ,, was thinking of using one of the smog pump actuators to stand in place of the egr, easy enough to rig up for a test i suppose.it feels just like something TPS , TFI or PIP related. id hate to have to swap out the stator just to shot gun it but i may have to. those hull effects like fuel pumps really dont give you any warning unless your really in sync with how your car "feels"Softtouch~ our kidding me right? this is an awsome tid bit, im seriously considering trying to understand where i missed out on this wealth of knowledge. i will do this sometime today and just pick any random solenoid to see if i hear it click and change states Quote Selected
minor engine stumble issue. Reply #8 – December 14, 2012, 04:01:12 PM I have never heard of this either, cool stuff.Try running a cylinder balance test at least twice in a row. Pretending its weak spark, bad timing, or fuel injector, it should show up here. That way you can rule out the individual fuel injectors or timing problem. Quote Selected
minor engine stumble issue. Reply #9 – December 14, 2012, 06:32:29 PM Quote from: jcassity;404534Softtouch~ our kidding me right? this is an awsome tid bit, im seriously considering trying to understand where i missed out on this wealth of knowledge. Emission Diagnosis Shop Manual Volume HC. Quick Test Appendices. Appendix D-- Output State Check (84 Shop Manual)You may want to check the EVP sensor voltage with key-on engine not running. Code 34 may mean the voltage is too high with the valve in the closed position. Voltage should be between .25V and .67v between the sense BR/LG and sig rtn BK/W. Quote Selected
minor engine stumble issue. Reply #10 – December 14, 2012, 08:50:10 PM Have you run KOEO with the EGR solenoid disconnected. I think the missing (open) solenoid should cause 83 or 84 Code. Don't think it should cause a 34 code. Quote Selected
minor engine stumble issue. Reply #11 – December 14, 2012, 09:49:40 PM no sir,have not done that. code 34 calls out this item though and it was a shorted diode that i cut out of the solenoid for test purposes.will also check the voltage like you mentioned.what i do know is i can not manually get air to pass from the lower to the upper vac fittings if i energize the solenoid. there must be crammed in there or something. tried carb cleaner and it flowed through slowly,, let it dry out then applied wd40, still cant blow through one tube out to the other with power on the solenoid. i can move some air but not much. Quote Selected
minor engine stumble issue. Reply #12 – December 15, 2012, 12:23:22 AM They call those EGR solenoids Vacuum Regulators. They replaced the old two solenoid set-up, where you had a control solenoid and a vent solenoid. The vacuum regulator does both the vacuum control and the venting with one solenoid. You should be able to move air into the nipple that goes to the EGR valve with the solenoid on or off. In one case it goes to the vent hole to atmosphere, in the other case it goes to the vacuum supply nipple. I don't know whether the solenoid being "on" connects it to the supply or the vent. Quote Selected
minor engine stumble issue. Reply #13 – December 15, 2012, 12:27:09 AM correct, de-energized the white vac line is to vent.--if i blow through it.If energized, i can blow ever so slightly through the the top and out the bottom but not much at all to the point im calling it nothing. Quote Selected
minor engine stumble issue. Reply #14 – December 15, 2012, 09:10:11 PM Holy ,Moving the throttle wide open and Letting it return deenergize is the EEC relay.Moving the throttle again once more wide open re energizes the EEC relay.Once more all characteristics of solenoids come into play depending on their state Quote Selected
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