Sluggish at higher speeds & after warming up...What's up?

[Thallarsen]

When I drive for short distances, everything seems fine; but after warming up and driving at highway speeds for awhile, the engine seems to go into a mode where it has sluggish acceleration and less power. Almost like I'm towing a trailer. Not much pinging or missing unless I step on it.
Usually it’s fine, and cruises up a steep hill at 80 without a heavy foot - but sometimes, it takes more gas to do it at 65 w/the same tank of gas, same conditions.
It seems like an ignition or mixture issue. I’ve recently replaced the plugs, wires, trans. modulator valve, thermostat and intake gaskets (retorqued after 2k), and run a few bottles of injector cleaner thru the system. I don’t think that it’s an intake problem, since I’ve checked the vacuum lines and retorqued the lower intake bolts. Also, the symptoms are sporadic as if it were a sensor that was acting up or something.
Recently, I replaced a faulty thermostat that kept the engine way too cold, I then disconnected the battery overnight to ‘reset’ the computer. I think it made a big difference, but I still have this little quirk.
Is there a sensor that effects mixture and/or ignition that may be to blame (EEC, IV, EGI or DIS)?
Also, regarding ignition timing:
On the sticker on the radiator housing, it says “...timing is not adjustable...” but it then says "...to check timing, disconnect small in-line spout connector...”. What/where is that?
I assume that if it advises on how to check the timing, there must be a way to ‘correct’ the timing through the various components (EEC, IV, EGI or DIS) if it’s not right. Otherwise why check it? Which component(s) make the timing right?
Any help/suggestions would be helpful.

 

[dogfriend]

Originally posted by Thallarsen
When I drive for short distances, everything seems fine; but after warming up and driving at highway speeds for awhile, the engine seems to go into a mode where it has sluggish acceleration and less power. Almost like I'm towing a trailer. Not much pinging or missing unless I step on it.

One explanation for this behavior is that the problem is occurring after the engine has gone into "closed loop" operation. This happens after the O2 sensor has warmed up enough to provide a signal to the computer to help determine proper fuel/air mixture. The computer uses this information to determine injector timing (which affects fuel/air ratio)

Usually it’s fine, and cruises up a steep hill at 80 without a heavy foot - but sometimes, it takes more gas to do it at 65 w/the same tank of gas, same conditions.
It seems like an ignition or mixture issue.

Going along with the above reasoning, I think its a mixture issue

I’ve recently replaced the plugs, wires, trans. modulator valve, thermostat and intake gaskets (retorqued after 2k), and run a few bottles of injector cleaner thru the system. I don’t think that it’s an intake problem, since I’ve checked the vacuum lines and retorqued the lower intake bolts. Also, the symptoms are sporadic as if it were a sensor that was acting up or something.

Vacuum leaks will usually cause rough idle. I think it may be a sensor or wiring leading to a sensor

Recently, I replaced a faulty thermostat that kept the engine way too cold, I then disconnected the battery overnight to ‘reset’ the computer. I think it made a big difference, but I still have this little quirk.

The thermostat problem would screw up the fuel/air ratio by tricking the computer. The coolent temp sensor sends a signal to the computer.
Is there a sensor that effects mixture and/or ignition that may be to blame (EEC, IV, EGI or DIS)?

There are several sensors which could affect the mixture and the ignition. EEC-IV stands for Electronic Engine Control, 4th generation and refers to the whole system of sensors, actuators and computer(s) that control engine functions. I don't recognize EGI. DIS (or EDIS) stands for Distributorless Ignition System (computer controls coil firing and timing)

Also, regarding ignition timing:
On the sticker on the radiator housing, it says “...timing is not adjustable...” but it then says "...to check timing, disconnect small in-line spout connector...”. What/where is that?

The SPOUT connector allows the base timing to be set at 10 deg BTDC. The SPOUT connector should be located near the ICM (ignition control module) which is on the driver side near the radiator. I don't know how to adjust the timing on your truck.

I assume that if it advises on how to check the timing, there must be a way to ‘correct’ the timing through the various components (EEC, IV, EGI or DIS) if it’s not right. Otherwise why check it? Which component(s) make the timing right?

the computer along with the ICM, the coil pack and the Crankshaft Position Sensor
Any help/suggestions would be helpful.

I would have someone scan for stored codes. One of the sensors may have an intermittent problem which is screwing up the fuel/air ratio. It is possible that it could be the O2 sensor(s) but it could also be another sensor.

 

[Thallarsen]

Dogfriend,
Thanks for the reply. I'm planning to get a code scan. What about cleaning the MAF? I've seen some posts about that, and some of them relate bad performance to a dirty MAF sensor. Any thoughts on that?

Thanks,
J.P.

 

[dogfriend]

Yes, a bad or dirty MAF could mess up the fuel / air ratio because it would be sending the wrong signal to the computer.

My Ford Fuel Injection book says the following sensors help determine fuel / air ratio during closed loop operation:

O2 Sensor (EGO or HEGO)
Engine Coolent Temp (ECT)
Intake Air Temp (IAT or ACT)
Throttle Position Sensor (TPS)
Mass Air Flow (MAF)
Profile Ignition Pickup (PIP) which signals engine rpm (the computer uses rpm and mass air flow to determine the load on the engine)

 

[Thallarsen]

Dogfriend,
Thanks again. I'm going to start with cleaning the MAF, reset the computer & see what that gets me.

J.P.