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To all the regulars out there I say hi. I am totally new hear and have spent my first 7 hrs. reading lots of good information. To my problem. Mine is similar to one posted the end of last month but not due to changing the alternator and my truck is a 91 not a 93. About 2 weeks ago I had new injectors and a new IP installed on my 91 7.3 IDI. I also had a new fuel heater and the housing the fuel filter attaches to replaced. This all due to poor starting and pratically no starting when cold. Anyway the tach just sarted going nuts about 3 days ago which made the truck up shift and down shift. As a wonderful side affect the OD light is dim and does nothing when you try to turn it off and on. With as fast as the problem started it went quickly the next days to no tach, and the shifting went to 2 and 3 manully only. I changed the tach sensor yesterday to no avail. I check all my fuses under the dash and looked for the TECA referred to on that 93 7.3 post. I did find the tailer tow relay that was referred to. I also found no place for fuses under the hood. I am sure it is something simple but hope it's nothing to expensive.
 

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You do not have the large plastic box on the drivers fender well............

If the tach is going nuts then ........

A dead tach sender should/would send the automatic trans into a "failure management mode" (limp mode) with harsh engagements and firm shift feel and an abnormal shift schedule. It has no effect on a manual trans only the Tach readings.
Check the wires where they exit the big nut on the oil filler housing , known to short out due to bare wire.....
Replace the tach sender on the oil fill housing a big 1" nut with 2 wires. Ford only part Engine RPM sensor E5TZ-17B384-A about $50. You can remove and clean it but usually changed later too.
You can test it too, hold it in the air away from ferrous metal, using an ohm meter lead on each wire you need DC resistance between 2000-3000 ohms.
 

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That explains why I found no fuse box under the hood. I did check the new tach sensor and it seems to be ok. I do understand it does not affect a manual but mine is automatic. The tach now does nothing and tranny when in drive takes off in 3rd. It will shift to what I believe is 2nd when done manually and reverse is fine. I am glad to see some replies and thanks for any and all replies :thumbsup:
 

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So where are you at in the fix now any improvements........ does the tach work yet any worn wires in the engine harnesses touching ground. Any flashing light on the OD switch.....
 

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So where are you at in the fix now any improvements........ does the tach work yet any worn wires in the engine harnesses touching ground. Any flashing light on the OD switch.....
No improvements. You can drive as long as you don't mind using the manual lever. The tach is now doing nothing and totally quit before I changed the sensor. The old sensor had one of the two wires that looked like it was pulled out of the sensor, which is one reason I changed it. The only connection anywhere that has problems in the one on the passenger side that feeds the "GP" relay. I had to remove and soder three of the wires. It was the two larger yellow ones and I forgot what color the smaller one was. Anyway I have tracked the wires checking any connection that seemed to be close to what wires tracked back to the tach sensor. The only thing I was wondering about was I washed the engine due to a oil leak from the large cooler line coming off of the filter. And I have a minor tapit cover leak. Maybe I got some water some where I shouldn't. But the problem began a full day after I washed it and I drove it alot before I gave it back to my supervisor. And the OD light is not flashing just on real dim.
 

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cdnsarguy rocks

Well just thought I would post that the problem has been solved!!!!! CDNSARGUY IS FULL OF GREAT INFO!!! The problem was the TECA relay and once I located it, thanks to cdnsarguy, three minutes and 15 dollars later I'm rolling. It was brought up in a post a month ago on a 93 7.3 and other than location of the relay being different than my 91, cdnsarguy had the answer. I guess what I'm trying to say is Thank You for all your help!!!:thumbsup:
 

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The TECA relay is located close to the test connector(s) on the firewall by the booster in the part location picture.

Fault identification is usually....... dim OD light with no or erratic gear selection or shifts.
 

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You guys are great. I had exactly this problem. On my 1994 it is relay #1 in the distribution box.

Relays can be ordered from partsamerica.com for $4.99
Nihoff part# RL36621
 

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hello I have a 1990 F-250 extended cab with the E4OD. I have been experiencing the low tach & dim Overdrive lamp on an intermittent basis. Replaced the Throttle position sensor today and reset the computer. All functioned normally for about 10 miles, when the tach dropped to 400 Rpm, and the OD lamp flashed dimly. The freeway speed was maintained. I saw this post and went and got a new TECA/ECC power relay. the tach is still at 400 Rpm. when the vehicle has been sitting awhile the tach will behave normally, but soon drops to low output. Any thoughts? I replaced the tach sender about 6 months ago as the old one was bad.
Jazzrockskier
 

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In my case I could idle the engine, plug in a good relay and the tach would work, and I could turn the overdrive OFF light on/off with the button on the shift lever.

When I pulled out the relay or diode (the 1994 model has them all in a box on the driver's side fender) then the tach would read zero and the OFF light would glow, and the button doesn't do anything.

So bottom line, if you don't trust your tach, use the OFF light to determine where you're at.

PS - I could feel the relay click while plugging it in (since the truck was already running). But when I pulled out the diode there was no power to the relay. It's probably protection against reverse battery hook-up. If your OFF light isn't working I would check the diode next.

I checked my owners manual and this relay powers the PCM computer. I'm surprised you can drive at all without having it working. On a EFI engine this would probably kill the engine, but since our trusty 7.3's are all mechanical they keep running.
 

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I have an E4OD auto transmission, so my OD switch and light are on the dash. Also on an E4OD the tach is fed from the ECC-IV shift computer instead of directly like the manual shift. The vehicle was started this am when cold overnite and the tach is functioning. Normally. But the low tach reading will return if i drive very far.
 

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This thread helped me out when I thought I was stuck: I had the same problem--reverse and manual gears work fine, but it starts and stays in 3rd in Drive... no tach and OD light always on. I replaced my EEC relay with NAPA part# AR-242 and it came right back to life! Even though the NAPA had 5 prongs and the old one had 4... the extra prong is N.C. and not used
 

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help please- what does the TECA relay look like, and where is it? 90 f250 7.3 IDI
thanks - im tracking down a draw...
 

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In my '94 it's one of the little black cubes in the fuse / relay box on the driver side fender

The older models had them under the dash and they were often metal cans. Not sure what year they changed.

A common source of a draw in my experience is the voltage regulator. With the ignition off there should be no voltage on the "F" (field) terminal of your alternator, or any terminal besides the big "BAT" terminal. If you do get voltage on any of the other terminals that's definitely wrong.
 

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okay, ive replaced all the relays in the little 'Relay 1 and Relay 2' box, as well as all the other relays in the fuse box right next to it, and my truck is still having the problem with the dim O/D light, no tach, and staying in 3rd. if i shift manually, i have to go from 1st to Drive, because it wont even go into 2nd gear. im hopelessly lost and in need of help. please help? :(
 

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If you changed relays the problem is most likely the connection at tranny pasenger side clean connection with die electric cleaner and grease with die electric grease. I would clean driver side connection to the mlps can cause trouble too.
 

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i looked for the one on the pass. side. i couldnt find it! :/
 

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Knowing what year your truck is really helps......... please put up a signature with truck year, model, etc......
 

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alright, ill do that. and i fixed the problem! well, after i had replaced the relays and checked every possible wire that i could, i just started pulling fuses in the black box under the hood. sure enough, i got 4 burnt out fuses. 2 Maxis! so i replace all of em, and shes back to the way she used to be! :) i just feel really stupid that it was something that simple. >.<
 

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I just bought an EEC relay NAPA part # AR-242, just to keep in my tool box for when it decides to go south on me when im on the road:lol:
 
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