• Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech

Code 77 and can't run CBT.

  • Thread starter Thread starter Hydrocarbon
  • Start date Start date Jun 11, 2004
H

Hydrocarbon

New Member
Nov 18, 2003
160
0
0
Medford Oregon
Jun 11, 2004
#1
  • Jun 11, 2004
  • #1
As the title says. I get a code 77 even though I goose the throttle, and I can't run the cylinder balance test.

I checked my TPS and it's .92-4.55. The only other codes I'm getting are 91/41 (system lean).
 

jrichker

StangNet's favorite TOOL
In Remembrance. Thank you for your contributions
Mar 10, 2000
27,512
2,813
234
Dublin GA
Jun 11, 2004
#2
  • Jun 11, 2004
  • #2
If the TPS has a bad spot on the resistor element, you could get a 77 code. Connect an analog voltmeter to the TPS and quickly press on the throttle. The voltage should increase smoothly to maybe 1.75-2.5 volts.

Typically, the CBT will not run properly if your IAC (aka IAB) isn't working correctly. If the idle is too low or to high, the CBT won't run correctly either.

Just for reference, and the benefit of others who might read this post, here is the short write up for the cylinder balance test.

Cylinder balance test:
Warm the car's engine up to normal operating temperature. Use a jumper wire or paper clip to put the computer into test mode. Start the engine and let it go through the normal diagnostic tests, then quickly press the throttle to the floor. The engine RPM should exceed 2500 RPM's for a brief second. The engine RPM's will increase to about 1400-1600 RPM and hold steady. The engine will shut off power to each injector, one at a time. When it has sequenced through all 8 injectors, it will flash 99 for everything OK, or the number of the failing cylinder such as 22 for cylinder #2. Quickly pressing the throttle again up to 2500 RPM’s will cause the test to re-run with smaller qualifying figures. Do it a third time, and if the same cylinder shows up, the cylinder is weak and isn’t putting out power like it should. See the Chilton’s Shop manual for the complete test procedure

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.dalidesign.com/hbook/eectest.html for more descriptive help
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html
 
You must log in or register to reply here.

Similar threads

Engine Vacc leak detector
  • Creomod
  • Jul 19, 2026
  • Fox 5.0 Mustang Tech
Replies
4
Views
116
Fox 5.0 Mustang Tech Jul 25, 2026
Mustang5L5
Electrical Code 29 again
  • Creomod
  • Jul 31, 2026
  • Fox 5.0 Mustang Tech
Replies
7
Views
153
Fox 5.0 Mustang Tech Monday at 3:10 PM
Creomod
2
Running very very rich
  • 2esoteric
  • Oct 31, 2025
  • Fox 5.0 Mustang Tech
Replies
4
Views
356
Fox 5.0 Mustang Tech Oct 31, 2025
Noobz347
M
Progress Thread 1993 Ford Mustang 5.0 convertible stock manual - ODB Codes shows running lean
  • mcalvo
  • Feb 11, 2025
  • Fox 5.0 Mustang Tech
  • 2
Replies
20
Views
1K
Fox 5.0 Mustang Tech Feb 22, 2025
AeroCoupe
S
Fuel ‘88 GT Runs Rich Cold — Fixes Itself When I Unplug Sensors (ECT, MAF, O2, etc.)
  • Sufarry
  • Nov 6, 2025
  • Fox 5.0 Mustang Tech
Replies
12
Views
883
Fox 5.0 Mustang Tech Nov 9, 2025
Mustang5L5
Share:
Bluesky Email Share Link
  • Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech
Menu
Log in

Register

  • Forums
  • What's new
  • Media
  • Resources
  • Contact
  • Sponsor
X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?

X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?