Detonation After Tfi And Egr Cleaning

To test your Egr, use a vacuum pump, apply about 10 inches of vacuum with engine off. If diaphragm in Egr is good it will hold on guage of pump. If it drops replace Egr valve. Test pump with hose plugged to be sure it's good and holding. Next, attach hose from pump, engine running, apply vacuum again, engine should stumble and die, if port is clear on intake. Also make sure your getting vacuum to egr hose going to egr. Verify timing with a timing light. 14-15 degrees is fine on 5.0 engines. If it didn't detonate before, it's got to be something you did, or uncovered. Keep us posted.


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What kind of TFI and what kind of goop did you use?

Code 34 Or 334 - EGR voltage above closed limit –

Revised 26-Sep-2011 to add EGR cleaning and movement test for pintle when vacuum is applied to diaphragm

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 clean or, replace the EGR valve ($85-$95).

Recommended procedure for cleaning the EGR:
Conventional cleaning methods like throttle body cleaner aren’t very effective. The best method is a soak type cleaner used for carburetors. If you are into fixing motorcycles, jet skis, snowmobiles or anything else with a small carburetor, you probably have used the one gallon soak cleaners like Gunk or Berryman. One of the two should be available at your local auto parts store for $22-$29. There is a basket to set the parts in while they are soaking. Soak the metal body in the carb cleaner overnight. Don’t immerse the diaphragm side, since the carb cleaner may damage the diaphragm. If you get any of the carb cleaner on the diaphragm, rinse it off with water immediately. Rinse the part off with water and blow it dry with compressed air. Once it has dried, try blowing through the either hole and it should block the air flow. Do not put parts with water on them or in them in the carb cleaner. If you do, it will weaken the carb cleaner and it won’t clean as effectively.

Gunk Dip type carb & parts soaker:



If you have a handy vacuum source, apply it to the diaphragm and watch to see if the pintle moves freely. Try blowing air through either side and make sure it flows when the pintle retracts and blocks when the pintle is seated. If it does not, replace the EGR.


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.

The following sensors are connected to the white 10 pin connector (salt & pepper engine harness connectors)


This will affect idle quality by diluting the intake air charge

if you have the stock intake and distributor, line up the marks on the distributor shaft and the lower intake and you will be at 10 BTDC. At least that will give you a safe base before you start playing with timng.

Remember to disconnect the "Spout" connector before trying to set the timing...

Martman said:

It still has the jerking maybe not as bad but still there.

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Here is a thread about your two codes. I found it interesting!!! The cross over tube in the back of the heads were clogged...
http://www.stangnet.com/mustang-forums/threads/code-94-44-again.817365/

The stall on cold engine points to timing being too far advanced; bucking under load at low speed is another symptom. Do the obvious: beg, borrow or buy a timing light and check the timing. Auto parts store will loan tools and test equipment if you have credit card.

Count on having to run 93 octane with 14° timing, particularly on an older engine that has a lot of carbon buildup in the combustion chambers.

Martman said:

Keep in mind the egr is was completely blocked and you can see the sludge from one of my previous threads.

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I can see from your pic that the cross over tube is still in place. Would it be hard for you to check it for clogs? It wont cost anything to check it reguardless.

jrichker said:

Count on having to run 93 octane with 14° timing, particularly on an older engine that has a lot of carbon buildup in the combustion chambers.

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You were the one that came up with the solution in the thread that I just read! Do you think that it would apply to this situation also? This is what you said in the other post:

Failure mode is usually due to a clogged air crossover tube, where one or both sides of the tube clog with carbon. The air crossover tube mounts on the back of the cylinder heads and supplies air to each of the Thermactor air passages cast into the cylinder heads. When the heads do not get the proper air delivery, they set codes 44 & 94, depending on which passage is clogged. It is possible to get both 44 & 94, which would suggest that the air pump or control valves are not working correctly, or the crossover tube is full of carbon or missing.

FoxtrotTangoWhiskey said:

I can see from your pic that the cross over tube is still in place. Would it be hard for you to check it for clogs? It wont cost anything to check it regardless.



You were the one that came up with the solution in the thread that I just read! Do you think that it would apply to this situation also? This is what you said in the other post:

Failure mode is usually due to a clogged air crossover tube, where one or both sides of the tube clog with carbon. The air crossover tube mounts on the back of the cylinder heads and supplies air to each of the Thermactor air passages cast into the cylinder heads. When the heads do not get the proper air delivery, they set codes 44 & 94, depending on which passage is clogged. It is possible to get both 44 & 94, which would suggest that the air pump or control valves are not working correctly, or the crossover tube is full of carbon or missing.

Click to expand...

That is correct, thank you for mentioning it.