1999 f250 7.3 Manual Early Build 6/98 ESOF 4x4 Ext CabLariat full size bed.
170,000 mi, Stock except 4’ turbo back exhaust (no cat,installed 6 mo ago); original PCM and IDM. No tunes. Filters and oils all up to date. No additives used for the 2.5 years I have owned this.

Recent work in last 200 miles: New clutch, oil pan, valvecover gaskets and harness (were all original); glow plugs (live in Northern Maine,it was time); exh backpressure sensor and tube (plugged and cracked); coolant temp sensor (part of the on-going effort to swap them all out).

There was an improvement in throttle response, lower rpm for a given speed (not much but noticeable), and general feel after these changes - likely attributable to the exhaust back pressure improvements.

Regarding Coolant Temp Sensor: Far as I can tell, there is only 1 ECT sensor. The Ford replacement sensor wouldn’t give a reading (needle lays flat, moves slightly as you plug/unplug). Aftermarket sensor pins the needle. The sensor that was replaced, which did register temp, was inadvertently tossed. Ohm checked the sensors and it is obvious they aren't the right range for the gauge. Waiting for the “proper” one from Ford. Ford dealer couldn’t tell me one way or the other whether there were 2 sensors or not. Reading other posts on here, the man trans had 2 and auto trans only the dashboard display. If there is another its on the back of the engine because it isnt where those with 2 sensors indicate where it supposed to be.

Not a problem though because the sensor located on the water pump is for display only, right? But now the oil pressure/coolant temp lamp stays on. Oil Press gauge reads normal.

After awhile the engine had starting (cold weather) andskipping issues. Replaced cam position sensor with OEM and that solved thoseprobs. Oil pressure/coolant temp lamp still stays on (not that I thought itwould make a difference on this).

What I have been noticing though is that in second gear, while accelerating mildly, the engine would “surge”. It seems like it is suddenly shifting into a different mode. The engine gets louder, but it doesn’t lead to a noticeable jump in acceleration. Shifting to 3rd seems to knock it back (based on noise, but hard to tell). No Service Engine Soon Light.

The rate of occurrence is increasing, meaning it happens most every time I first start out, whereas before it was once every 3-4 trips. Seems to happen when the engine is “cold”, although it idles for upwards of ˝ hour before I take off. After driving around for awhile (local driving), it stops doing it.

Don’t have code pulling capability. Aside from noted issues, the truck runs well. 14.5-15 mpg on “city” driving (no long highway runs) with much warming and idling. No ugly smoking on start-up (a minor puff of bluish/whitish smoke on ignition, but clears up quickly, even when below zero and not plugged in).

Any thoughts?

Thanks in advance and thanks for all the institutional knowledge on this site.


Also, a beverage of choice (if you come to northern Maine) or eternal gratitude to whoever can produce that 1 page schematic showing sensors and PCM pins for the early builds. Rumor has it the 2000 diagram doesn't cut it.

 

7.3 base their temperature reading from the oil temp sensor located on the hpop oil reservoir not the coolant temp sensor.
The surging when cold sounds like either your UVCH has burnt pins/connectors, check those out first.

 

OK on the oil temp. I guess I missed that on all the reading. Is that an artifact of early builds? From what I picked up, man trans had 2 coolant temps, with one of them providing info to PCM. On auto trans, temp for PCM was pulled from transmission temp.


Harnesses are new, but something could have got screwed up there. Although the change in engine pitch started sometime after I changed them. What is puzzling is that it only happens in 2nd gear, and up to when the truck finally warms up fully.


Thanks for the input.