1990 5.8 Bronco no start

[EJ in GA]

So it was running fine then hesitated a couple of times. Shifted oddly also then died. Replaced fuel pump relay because it’s cheap and easy. Wasn’t getting power at fuel pump so replaced that. Now not getting power at the relay. I noticed the light under the hood wasn’t on either. My buddy ran a jumper wire from battery to relay, light came on and it started normally. Today I opened hood and the light was on, charged the battery and it fired up. Ran for about 10 minutes and check engine light would flash as the engine would sputter. Did this about 4 times and now it won’t start again. The light under the hood is also off again. I was told it may be the ECU????

 

[miesk5]

Yo EJ,
WELCOME!
Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19
The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test

Troubleshoot a No Start Ford 4.9, 5.0, 5.8 @ https://troubleshootmyvehicle.com/ford/4.9L-5.0L-5.8L/how-to-troubleshoot-a-no-start-1



EEC IV CONNECTOR PIN DIAGRAM by Ryan M.

EEC IV Connector Pin LEGEND by Ryan M.

Check PCM GROUND;
All resistance tests should be done with the ignition key in the off position. Having voltage going through the system can return a false reading of excessive resistance. Additionally, it is possible to have a ground that tests OK when the engine is cold, but not when the engine is hot. Heat increases resistance, so these tests should be performed on a warm engine when possible.
To test for an adequate ground circuit in the EFI system, use a Volt/Ohm meter to check the resistance of the following circuits. Disconnect PCM Connector:
To verify a proper ground to the PCM, check the resistance from pins 20, 40 and pin 60 DIRECTLY to the negative side of the battery Post.
Of course, battery must be fully charged and test @ 12.6 volts no load with engine off; posts must be rigid; ground cables, connector, and grounds must be clean and tight.
Resistance should be no greater than 0.2 ohms.[/B]
Replace faulty wiring between computer and battery if not.

Some Possible Symptoms Of A Failed Computer:

• No start. Rough start. Slow cold start.
• Poor fuel economy.
• Loss of power.
• No communication.
• No injector pulse.
• No ignition pulse.
• Intermittent problems.
• Electrical problems.
• Fault/ trouble codes.
• Shifting problems.
• etc.......

●
Here are the 1990 Bronco Pre-Delivery Shop & Electrical & Vacuum Troubleshooting Manuals (EVTM), Partial by member Kingfish999 in Google Drive @ 1990 Ford Truck service manuals - Google Drive
&
1990 Ford Truck Emissions Manual.pdf by Ford via member 90.CaliBronco in Google Drive @ 1990 Ford Truck Emissions Manual.pdf

Suggest you download both for faster scrolling and to use the table of contents index.

1990 Ford Bronco Brochure by Ford via Dezo's Garage @ https://www.xr793.com/wp-content/uploads/2020/07/1990-Ford-Bronco.pdf

Haynes Red Manual for 80-95 Bronco & F Series @ Hanes guide 80-96 bko f series.pdf found by BroncMom!

Al

 

[miesk5]

Yo,
I overwrote;
EEC IV PCM Removal up to & include 87- 91 COMPENDIUM;
"To remove it first disconnect battery & get use 10 mm socket to unbolt the wiring harness "connector from inside the engine bay. Then pull plastic kick panel from inside cab & remove the retainer clip Remove it by lifting rear slightly & wiggling it out of the "pocket" ... the firewall rubber gasket will have a pretty good grip on the connector so it will take some persuasion to free. "
"...Remove driver's inside kick panel adjacent to pedals. It comes out through cabin." by Seattle FSB;
"Should be one small metal ***** holding it. Just slide it out, but be careful w/ gasket for firewall. Don't mess it up, you can reuse it." by Darth_ted_82
"You have to unplug it under the hood very low on the fire wall (10 mm socket)."

Hhere are some EEC IV PCM KILLER perpetrators and other causes:

Smell around the PCM. If it smells like dead fish, it's bad.
Look for PCM printed circuit board burn marks around leaking capacitors, resistors.
View attachment 182797
For example, see Old leaky capacitors in swapped EEC and no more codes by jowens1126
Water damage from cowl leaks, ESPECIALLY if you you have wet carpet or mat near driver kick panel; or on PCM Connector due to a bad hood seal near cowl panel, viewable with hood up.
Corrosion or damage due to moisture is one of the main reasons for failure. Corrosion can enter through the wiring harness and moisture can enter by a failure in the seals in the PCM itself. This happens over a period of time (5 to 10 years) due to exposure to the elements.
The alternator could be generating an AC voltage spike due to bad diode(s) or supply Voltage
View attachment 182796
Overloads.
I recommend bench-testing the alternator for voltage output and AC voltage ripple.
Thermal stress due to excessive heat and excessive vibration that causes sensitive parts to fail.
Bronco was jump started on reverse polarity.
Connector pin damage or corrosion,
Other internals:
broken tracks,
cold solder joints,
short circuit,
thermal stress due to excessive heat and excessive vibration that causes sensitive parts to fail,
Overheated PC,.
Bad Intel 8061 chip or bad Intel 8361 memory chip,
Bad Internal Voltage Regulator, see Wayback Machine by absent member Fireguy50 (Ryan M)

 

[EJ in GA]

Found the problem. Loose wire on the solenoid. Got lucky this time. Something simple. Just took time chasing wires.

 

[Motech]

I love it when simplicity tickles us back down out of the tech clouds!