Engine Stutter

I had a similar problem with my 91 5.0 when I first bought it. I did plugs, and then wires. It turned out the wires were the issue. Hope you get it figured out.

Does it happen all the time or just under WOT? What rpms?

I would add a fuel filter on my list of things to start with. A clogged filter could cause that...

I think the best place for you to start would be to pull codes from the computer. Even though there is no check engine light there still may be error codes stored in the computer. Search this forum for how to do this with a paper clip....i do it all the time very simple and quick. No diagnostics tools necessary. Secondly...the standard autolite plugs are the BEST....i know that you may think that a less than 2 dollar plug is the best for a Hi-perf application....but a lot of guys on this forum, myself included, swear by them. pull codes...leave those plugs in there and let us know what you come up with.

This code depends if you completed the key on engine off diagnostic test or the key on engine running test. If it was the KOEO then code 34 trips for EVP sensor voltage out of rang...too high. This is the electromagnet that controls the operation of the EGR valve. The white sensor on the back of the EGR valve. If the code came up in the running test then 34 is for EGR valve opening not detected. Check the operation of the EGR valve using a supplied 10" of vacuum. You should also remove it, check the diaphragm for cracks or leaks, then check the pintle for excessive carbon build up. Clean the whole thing and reinstall it. Also check the vacuum supply hose to the EGR to check for any leaks or cracks.

Code 34 Or 334 - EGR voltage above closed limit - Failed sensor, carbon between EGR pintle valve and seat holding the valve off its seat. Remove the EGR valve and clean it with carbon remover. Prior to re-installing see if you can blow air through the flange side of the EGR by mouth. If it leaks, there is carbon stuck on the pintle valve seat, replace the EGR valve ($85-$95).

If the blow by test passes, and you have replaced the sensor, then you have electrical ground problems. Check the resistance between the black/white wire on the MAP/BARO sensor and then the black/white wire on the EGR and the same wire on the TPS. It should be less than 1.5 ohm. Next check the resistance between the black/white wire and the negative battery post. It should be less than 1.5 ohm.

Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.

Let’s put on our Inspector Gadget propeller head beanies and think about how this works:
The EGR sensor is a variable resistor with ground on one leg and Vref (5 volts) on the other. Its’ resistance ranges from 4000 to 5500 Ohms measured between Vref & ground, depending on the sensor. The center connection of the variable resistor is the slider that moves in response to the amount of vacuum applied. The slider has some minimum value of resistance greater than 100 ohms so that the computer always sees a voltage present at its’ input. If the value was 0 ohms, there would be no voltage output. Then the computer would not be able to distinguish between a properly functioning sensor and one that had a broken wire or bad connection. The EGR I have in hand reads 700 Ohms between the slider (EPV) and ground (SIG RTN) at rest with no vacuum applied. The EGR valve or sensor may cause the voltage to be above closed limits due to the manufacturing tolerances that cause the EGR sensor to rest at a higher position than it should.



This will affect idle quality by diluting the intake air charge


Codes 94 & 44 - AIR system inoperative - Air Injection. Check vacuum lines for leaks, & cracks. Disconnect the big hose from smog pump: with the engine running you should feel air output. Reconnect the smog pump hose & apply vacuum to the first vacuum controlled valve: Its purpose is to either dump the pump's output to the atmosphere or pass it to the next valve. The next vacuum controlled valve directs the air to either the cylinder heads when the engine is cold or to the catalytic converter when the engine is warm. Disconnect the big hoses from the back side of the vacuum controlled valve and start the engine. Apply vacuum to the valve and see if the airflow changes from one hose to the next.
The two electrical controlled vacuum valves mounted on the rear of the passenger side wheelwell turn the vacuum on & off under computer control. Check to see that both valves have +12 volts on the red wire. Then ground the white/red wire and the first solenoid should open and pass vacuum. Do the same thing to the light green/black wire on the second solenoid and it should open and pass vacuum.

Remember that the computer does not source power for any actuator or relay, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.

The computer provides the ground to complete the circuit to power the solenoid valve that turns the vacuum on or off. The computer is located under the passenger side kick panel. Remove the kick panel & the cover over the computer wiring connector pins. Check Pin 38 Solenoid valve #1 that provides vacuum to the first Thermactor control valve for a switch from 12-14 volts to 1 volt or less. Do the same with pin 32 solenoid valve #2 that provides vacuum to the second Thermactor control valve. Starting the engine with the computer jumpered to self test mode will cause all the actuators to toggle on and off. If after doing this and you see no switching of the voltage on and off, you can start testing the wiring for shorts to ground and broken wiring. An Ohm check to ground with the computer connector disconnected & the solenoid valves disconnected should show open circuit between the pin 32 and ground and again on pin 38 and ground. In like manner, there should be less than 1 ohm between pin 32 and solenoid valve #2 and pin 38 & Solenoid valve #1.

If after checking the resistance of the wiring & you are sure that there are no wiring faults, start looking at the solenoid valves. If you disconnect them, you can jumper power & ground to them to verify operation. Power & ground supplied should turn on the vacuum flow, remove either one and the vacuum should stop flowing.
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

Disabling the emissions equipment can cause the computer to go into limp mode and set the Check Engine Light. Limp mode means reduced performance and fuel economy. I recommend that you learn how the emissions & computer system work before disabling something and shooting yourself in the foot.

Here's a book that will get you started with how the Ford electronic engine control or "computer" works.

Ford Fuel Injection & Electronic Engine Control 1988-1993 by Charles Probst :ISBN 0-8376-0301-3.

It's about $25 from Borders.com see http://www.amazon.com/ . Select boo...very good, and I found it to be very helpful.

The EGR uses the vac line to move the diaphram in and out. After you get it all back together and test drive it, if the problem doesn't go away...try unhooking the vac line to the EGR itself (block the vac line off) and see if that helps.

Like I said, I had the exact same problem as you described along with the same code. I unhooked the vac line and the problem went away. I have since removed the EGR all together.

i am having egr issues too. i just took mine off last night. there was vacuum on the line going into the egr when i disconnected it, if that helps at all....

the 2 hoses on the egr spacer just run coolant throught it, to cool the egr gasses that enter. i have heard both good and bad from disconnecting them from the egr, but they should not have anything to do with the vacuum. if they are just capped, i think you should maybe put a connector between them if u want to bypass the egr, rather than just cap. i had mine connected to bypass for a while, but i decided to put them back on after reading up on it a bit. i have no smog either, but i do get vacuum on the hose into the egr (while running, just to be clear!), verified by FINGER! good god man! maybe u can tell me what a MAF sensor is supposed to taste like? i'm getting an error on mine!