well the bronco has been acting up again...
its a 1993 ford bronco 351w efi automatic 4x4 xlt
The check engine light comes on, it shifts real hard and fills like its being choked, real low idle and it about or does die.
went to auto zone to pull codes and i got:

112. act/iat sensor circuit below min. volt.
117. ECT circuit sensor below min. volt.
122. TP sensor below min. volt.
126. MAP/BARO sensor higher than expected
327. EGR circuit above min. volt.
513. internal volt. fault
553. secondary air injection diverter circuit fault
552. secondary air injection bypass circuit fault
564. fan control circuit fault
556. fuel pump relay primary circuit fault
558. EGR (EVR) circuit fault
631. transmission control indicator lamp circuit fault during KOEO test
622. shift solenoid no. 2 circuit fault
638. 290 deg. F indicated by TOT sensor, or sensor circuit below minimum volt. circuit shortened
654. MLP sensor not indicating PARK during KOEO test

and there was more but the guy at auto zone was like its probably one thing causing all of the codes so he didn't get the rest.

last time it acted up similar to this i just changed the fuel pump, fuel filter, and PCV valve. It seemed to run great for about a month then it acted up again
your help would be greatly appreciated thanks

 

Sounds like you may have either a battery or alternator issue. Does it store a charge and restart ok ? Has it blown any fuses ?

 

it has a brand new battery not sure about the alternator starts fine and i've checked the fuses none of the ones that control the problems are blown

 

Never mind... listen to greystreak

 

it was key on engine off KOEO
and i appreciate your info
ill see what i can do tomorrow

 

Sounds like a messed up ECU or a short to me.

 

Mmmm boy... I've been away too long... ok, nothin; like jumpin' in head first.

ALL of the Codes indicating "below minimum voltage" indicate a problem far greater than the individual sensors and troubleshooting techniques themselves. Code 513 is the tip-off here. Code 513 indicates that the VREF power supply has failed. In other words, you aren't getting VREF which is provided by the +5VDC transformer IN the EEC-IV computer. I don't typically make this recommendation because failure of the EEC-IV computer is so damned rare. However, in this case, its time to look for a new computer. The VREF power supply cannot be replaced independently of the EEC-IV computer. There really is no point in attempting to diagnose anything else until this issue has been resolved.

You may be thinking to yourself, "but how the hell is the truck still running then if this part of the system has failed?" Simple, the EEC-IV computer has a fail-safe program that allows it to continue to operate the engine well enough to idle and drive using pre-programmed parameters even if it cannot get sensor information. Affectionately called "limp" mode, it will "get you home" but makes the truck run about the way you described in your initial post.

 

well would the check engine light cut on and off and run perfectly for a while then mess up and go back to normal if it was that?

 

Intermittent operation like that COULD mean you have a short or loose connection somewhere. The way to check would be to take a voltage reading between pin 26 (ORANGE/WHITE) wire of the ECM and NEGATIVE (frame of the truck or battery NEG.).

You should get approximately +5VDC reading. It can fluctuate a bit but should be no lower than +4.75VDC. If the reading checks out at the ECM, it can be checked again at the main harness connector under the hood and again at each sensor but since the issue would appear to be upstream of the sensors and at a main connection point or in a main wire from the power supply, this would be the path to start checking beginning at the output of the ECM itself first.

 

thanks ill have to test it

 

well i went and got a computer off a downer 93 bronco and put it on and so far so good its on the roads again thanks everyone for there help

 

well problems are back....
engine light keeps coming on and running like crap or dieing then dosent seem to want to get any gas till it sits for a while, so guess back to the drawing board
only thing i can figure would be a short or a sensor any suggestions?

 

To me it seems like a wiring harness issue, first i aimed at the ECU, since that didn't do it, check the harness.

 

The scariest part of this is the fact that it could be a wiring short that took out the original ECM. Is there any part of the wiring harness (particularly in the engine bay) that you know of that suffered any damage. Melt down from getting too close to exhaust system components and physical damage from being pinched or frayed are things I would look for first.

In my experience the section of the main harness that runs across the top of the cowl is most frequently exposed to damaging heat from the exhaust system when the check valve on the Thermactor air injection crossover tube fails. I know that's a mouthful of description but the crossover tube runs behind the cylinder heads and connects the air injection ports in the heads. The check valve come straight up from the middle of the crossover tube and a hose runs back to the diverter valve near the back of the right cylinder head. When the check valve fails it either snaps in half leaving exhaust to blow straight up at the wiring harness above it or the hose melts and the exhaust still gets through. Not saying this is the culprit but it is common enough that it might be worth looking into.

 

Don't throw the old computer away. Dig it out of the trash because the numbers have to match the new computer.

Check the grounds next to the code pulling connection and the two next to the battery and your battery to fender pigtail.

Your donor PCM may have issues also. Age and heat break down the cheap capacitors that were used. Sometimes they leak and damage the board also. It is a matter of time until they fail. I have had a like new running Bronco for a year now after ECMTOGO.COM repaired mine. Print two copies of their send form and send one with the PCM. They will test it and let you know if it is repairable (mine was $195 + frt +tax). If not repairable they have replacements. One year warranty. Remember the numbers on the PCM must match.