Idle Fluctuation

Alright guys. i have replaced the idle air control valve, cleaned it out 3 times, replaced the oxygen sensor, cleaned out the throttle body and my idle still fluctuates and almost dies and it sort of has a high idle also. and i was getting 13 mpg and now i'm only getting 8.4 i've changed the oxygen sensor and got a tune up neither has helped. need some help. thanks

yo

Go back to your other post here @ http://broncozone.com/topic/22587-transmission-or-something-with-throttle/page__p__117816#entry117816

Tey the test for codes, vacuum leak tests advised there

Post codes found here.

already tried that. something is wrong with the computer and it won't read codes.

yo JAKE,

ok

You have a 90, Bronco, correct?

If so and you can take time to electrically and visually troubleshoot w/ digital multimeter;

run a ground wire from Scan Tool or from the DLC "Self Test Input" to Battery Negative Post

This will replace what JOE Describes as; Put the jumper wire as indicated between "Self Test Input" and "Signal Return� Ground"

This is in case that "Signal Return� Ground" circuit is damaged or a bad ground (usually @

for Scan Tool grounding



by Jeremy M (Big '92, jermil01)

================

Next Set of troubleshooting;

NO CODES Troubleshooting by Ryan M (Fireguy50) at http://oldfuelinjection.com/?p=44'>http://oldfuelinjection.com/?p=44

http://oldfuelinjection.com/?p=44

excerpts;

Check Battery voltage, must be above 10.5 volts.

•Replace battery if not.

•Check battery connections, corrosion, ground faults, and wiring.

• Fix all wiring.

•Check alternator output, must be between 13.5 and 14.5 volts.

•Replace Alternator if not.

•Any recent voltage irregularities from electrical charging system can cause failures.

Check EEC relay, must show battery voltage when engaged.

•Replace relay and damaged wiring if not.

•Make sure pin 30 on the computer is hooked up correctly.

•Manual transmission computers need to sense SIG-RTN on pin 30 when in neutral.

•Automatic transmission computers need to sense Ground on pin 30 when in neutral.

READ MORE

to help go thru the steps;

Here is Ryans EEC IV PIN LEGEND

http://oldfuelinjection.com/truckpinouts.html

& EEC IV Connector Pin Outs

http://fullsizebronco.com/forum/attachment.php?attachmentid=17644&stc=1&d=1313769200

Hey Jake,

This may be another case of bad grounding. If you have no ground at the comp. it has to be effecting other systems as well.

On a vehicle 22yrs old, check all the grounds.

Good Luck

yo

The Scan Tool grounding I posted alleviates a bad Ground ckt from that "Signal Return� Ground" though the EEC and to the grounds at rad support (see pic below)

the EEC (computer) ground comes from two main sources, one is the body/frame ground (G104) and the other is the small black wire that goes directly to the negative terminal of the battery (G101/102). G104 goes to EEC Pin #20 and the TFI ICM. G101/102 goes to EEC Pin #40 & 60. This a direct ground to the battery(-) post and the connection on the radiator support is frequently the cause of problems. It can also corrode developing a poor connection at the negative battery cable connection at the battery post.

yo,

Update on Ryan's URLs

CHANGED following on 14 JUL 2014:

Ryan's EEC IV PIN LEGEND at http://web.archive.org/web/20131029020805/http://oldfuelinjection.com/truckpinouts.html

& his EEC IV Connector Pin Outs at http://web.archive.org/web/20131229163930/http://oldfuelinjection.com/images/eec04.gif