With that approach, it makes it very difficult to troubleshoot. Obviously, SOMETHING is wrong. One of your new or clean parts is causing the problem. Unless you've tested it and verified it to be working, it is suspect.

If everything has passed the PCM test, something could still be out of spec enough to cause problems but not throw a code. Have you tested the EGR with a vacuum pump? Have you checked the TPS? IACV clean? Throttle body clean?

 

Yes, this is difficult to troubleshoot. The funny thing is that I did not have this problem BEFORE I removed the motor and put it back together with all new parts.

Anyways, the IAC (Nappa's best) and throttle body (original) are very clean.

I checked TPS (Motorcraft) with a digital volt meter at closed throttle (0.95 v) and wot (4.5v) and check it between closed throttle and wot very slowly with an analog volt meter set to a 0v-5v scale looking for any erratic movements in the needle. There were none.

As for the EGR the only thing that I have done to test it is to apply vacuum with the engine off and see if it hold vacuum. It did. Then with the engine running (trans. in park, 1200 rpm), apply vacuum and see if it runs rough, then remove the vacuum and see smoothens out. It ran rough with the vacuum the smoothened out when I removed vacuum. Plus, I have tried 2 different EGR valves (Motorcraft) and nothing was different with either one.

Edit:

While testing the EGR, I was sucking on a hose. I did not use a pump with a guage because I did not have one at the time.

 

Can you clarify something for us?

Earlier, you said: "It will start up and have the normal high idle of about 1100 and hold it for a few seconds. Then it will almost die (400-500 rpm), then shoot up to 1000-1100 rpm and repeat this cycle."

Then you just said it smoothed out when you removed the vacuum. I'm just asking you to elaborate a little, because I want to be sure we're clear on what the problem is.

 

+1. It is the bible on OBD-I systems. I just wish Dr. Probst could have lived long enough to write a book on the OBD-II system.

The ECT works like an automatic choke on a carburetor. When cold, if the ECT is bad, the truck will be hard to start, will stumble, try to die, spit back, etc. It does this because the computer thinks the engine is warm, and is not adding additional fuel to richen up the cold air coming into the engine.

The severity of the symptoms will depend on the outside temperature. The warmer the ambient temp., the less sever the symptoms.

For the erratic idle, I would test TPS with a known good one. A problem with this sensor does not always set a code. The resistance/voltage check is not that reliable. I had one instance where the total resistance of the sensor had changed, and was a bear to start and keep going. jd

 

"It will start up and have the normal high idle of about 1100 and hold it for a few seconds. Then it will almost die (400-500 rpm), then shoot up to 1000-1100 rpm and repeat this cycle."

Thats what the motor does if I fire up the motor and let the motor run without touching the throttle or doing anything else.



"Then you just said it smoothed out when you removed the vacuum"

When testing the EGR I had the motor @ 1200 rpm by placing a few feeler guages (I forgot how thick they were) on the throttle stop screw to hold the throttle open a bit. At 1200 rpm and up the motor does not surge and that is where I do most of my testing at.

The motor smoothed out once I removed the vacuum (the vacuum that I gave it myself, not vacuum from the motor) from the EGR. That would indicate that the EGR is good.

 

jimdandy,

I already substituted the TPS with known good, and nothing changed.

 

As for the book...

Ford Fuel Injection and Electronic Engine Control by Charles D. Probst

I am interested. It seems that there were 2 of them. One for 80-87 that covers EEC-3 and EEC-4 and another for 88-93 that covers EEC-4.

My question is...

What changed from 87 to 88?

My rig is an 88, so I guess it's a no-brainer which one to get, but what is the difference between the contents of these books?

 

Ok grena, makes sense now. I need to go ponder for a bit.

As far as trucks go, EEC-III means the feedback carb setup. EEC-IV means multi-port fuel injection as most of us know it. EEC-V means ODB-II.

I have the EEC-IV version - it's a great reference.

 

Not trying to re-hash a earlier discussion but isnt the map sensor one of the first to be used.

Before startup dosent it record the the barometric pressure without the motor running then when the engine is running it will begin recording manifold pressure once warm?

 

Yes, MAP sensor is the primary load sensing device on these speed density EFI systems. Yes, barometric pressure is recorded as reference when the key is first turned on, before the engine is started. Once the engine is running, the computer uses the MAP sensor to determine engine load - it doesn't wait for the engine to warm up, it begins as soon as the engine is turned over.

 

Had the same problem on my 93 5.0, along with a few other problems. First suggestion is to make sure there are no vacume leaks. Changing the ignition modual fixed this problem for me, hope it helps you.

 

You are talking about the TFI module on the side of the distributor...right?

How did you diagnose this?

 

thanks this helps me out a lot

 

FYI - EEC-IV was installed in 83 models and up// so 83-87 EEC-IV is in the older book - 1980-1987

 

Did you ever get this fixed..........??