Help!!!!!

I have a 1996 Bronco 5.8 it has been in the shop for two weeks . We are not sure what is wrong at this point , a new fuel pump is going in on Wed.  I have replaced all relays and I should note that the fuel pump is two years old . The computer has been replaced twice now and when you start it  is showing gradual lose of the injector pulse. I have fuel pressure but takes some time to come up it runs at 30 psi and starts up at 40 psi, when you turn it off the pressure drops off to zero. Test light on the injector shows it getting weaker and in about 15 to 20 seconds the light goes out all together. the engine will not start at this point even though you have fuel pressure , if you turn the key off and try restart it may fire but most times now it will not run.  

Thanks for any ideas at this point, its about time to get rid of this money pit. (

Hey George,

When you say a loss of injector pulse I assume you are speaking of the electric pulse to open and close.

The injectors get their power from the PCM power relay via a red wire, and are energized by the PCM through different colored wires indexed for the individual injector.

If you are seeing the voltage drop via a test light to the red wire and a common ground, I would first test with a voltmeter to confirm the voltage drop.

Then check for the same voltage drop at the red wire out of the PCM power relay. Next check the voltage at the yellow wire supplying power in to the relay.  No voltage drop there?...you have your "gremlin"

If there is still a voltage drop at the yellow wire, check fuse 9 at both ends. Possible problem with a loose connection in the fuse box. There can be a situation where a wire is barely making contact. Then as current is drawn through, the wire gets heated and the connection is broken.

I know it's a pita, but patience, and a good head will get you through this one

Good Luck.

Thanks, We are having no voltage drop as you suggested in your response, what we are seeing is the lose of ground signal from the computer, I should mention that we have put in two computers at this point. ???  Thanks 

How odd!  You loose the ground signal to all  the injectors?!      Have you checked the ground to the PCM, and the body and engine grounds? Is there a good, known constant ground to the PCM?

Ok he is going to check this, he did say that when the light goes out that you can turn off the switch and turn it on and the test light on the injector is reset? They have installed a new ignition switch and still no go.

Have you done the tests, or is this all info from the shop?   Sounds like they are just guessing.  I would be suspect of loosing all the ground signals, unless I saw it myself.

What is the logic in changing an ignition switch, or fuel pump, if you are loosing a ground signal?

They have been working on this for a few weeks now. I just talked to my guy and he is going to do the ground tests and they are just really stumped at this point. I will get back as soon as I hear anything. Thanks

Finding the cause on this will be valuable info for a lot of others.

Good Luck  

yo George,

What are the symptoms?

Such as a Misfire?

Also the Check Engine Light (CEL) comes on when the electronic engine control system is not working properly. The check engine warning indicator comes on briefly when the ignition switch lock cylinder is turned to ON, and should turn off when the engine starts. If the check engine warning indicator does not come on when the ignition switch lock cylinder is turned to ON or if it comes on while the vehicle is moving, the system is malfunctioning
If the CEL does not light up at all when starting it; then suspect that bulb is burnt-out or loose, socket was damaged by PO or shop, etc. or someone removed it.

Is the CEL lit while driving?

Did the shop check for Codes?

Does the shop have the FORD 1996 Bronco Powertrain Control/Emissions Diagnosis,  OBDII to do the Pin-Point testing?  If not... time to find a shop that does have it.

I have a 96 Bronco PCED CD, but it is not loading.

GROUND Locations & Components in a 96 by me

http://broncozone.com/topic/20952-loose-ground/page__pid__109954__st__0&?do=findComment&comment=109954

excerpts:

G101 front of engine compartment, front of fender apron (D1) - RH = Passenger side mine has 2 small black wires between starter relay & headlight; this is #5 in the diagram;

Powertrain Control Module (PCM), 5.0L
Powertrain Control Module (PCM), 5.8L

G104 Serves Component: (G100 & G104 (tied together, see location diagram))
Component
4WABS Control Module
4WABS Data Link Connector
4WABS Relay #1
Instrument Cluster
Powertrain Control Module (PCM), 5.0L
Powertrain Control Module (PCM), 5.8L
Programmable Speedometer/Odometer Module (PSOM)
Trailer Relay Box

G103 (battery to engine) Lower RH front of engine
Component
4WABS Pump Motor
Battery
Data Link Connector (DLC)
Mass Air Flow (MAF) Sensor
Powertrain Control Module (PCM), 5.0L
Powertrain Control Module (PCM), 5.8L
Right Front Park/Turn Lamp
Right Front Side Marker Lamp
Right Headlamp

G103 (battery to engine) Lower RH front of engine Component
4WABS Pump Motor
Battery
Data Link Connector (DLC)
Mass Air Flow (MAF) Sensor
Powertrain Control Module (PCM), 5.0L
Powertrain Control Module (PCM), 5.8L
Right Front Park/Turn Lamp
Right Front Side Marker Lamp
Right Headlamp

 

The shop has all the latest OBD checks and the computer is not putting out any codes. they have a link to Ford as well these guys are good at what they do. Thanks to everyone for the help and I will post when we or if we find the problem????  No misfire just start sometimes and then no start.

yo,

All this is by Ford for our 96 Bronco;

TANK-TO-INJECTOR FUEL INJECTION SUPPLY MANIFOLD REMAIN UNDER HIGH PRESSURE AFTER THE SYSTEM IS SHUT OFF.

The supply check valve, which is normally closed, opens when the outlet pressure from the energized pump exceeds the opposing check valve spring force. When the fuel pump is de-energized (i.e., engine is shut off), the supply check valve closes to maintain pump prime and fuel supply tube pressure.

The in-tank mounted fuel delivery module containing the fuel pump is capable of supplying 105 liters (27.7 gallons) of fuel per hour at a working pressure of 270.0 kPa (39 psi) for the 5.0L, 5.8L and 7.5L MFI engines.

Pressure in a 96 with;

Ignition On, Fuel Pump Running = 35.0 - 45.0 PSI

At Idle = 30.0 - 45.0 PSI

=====

Freeze Frame Data & No Codes; Another advantage of OBD II is the freeze frame data function of the scan tool. Whenever an emissions related DTC is set, the MIL will illuminate and a freeze frame will be set in the PCM’s memory. The freeze frame should contain, but isn’t limited to, the following data: Engine load (calculated) , Engine RPM , Short- and long-term fuel trim, Vehicle speed, Coolant temperature, Intake manifold pressure, Open/closed loop operation, Fuel pressure (if available), DTC; In this generic scan tool feature, you can’t get DTCs. But you can get a serial data stream that will update a minimum of two times a second. More importantly, you will have access to at least 16 data parameters and a 66-frame movie of ECU/PCM data. The most important function of any scan tool is to diagnose intermittent problems. Listed below are my reasons why the movie/snap-shot is so valuable! On slower baud rate systems, an out-of-range sensor may take several frames of data before a DTC is set. But it would still cause a noticeable driveability problem on the vehicle. And it still might not set a DTC. Duplicating the customer’s complaint with a road test and a movie/ snap-shot may be the only way to properly diagnose the vehicle..." READ MORE
Source: by Gary G at http://web.archive.org/web/20090107104307/http://www.asashop.org/autoinc/november/scantool.htm

 

 

a wag;

LONG CRANK/STALL AFTER START-IAC VALVE STICKS - REV3

TSB     96-22-3

http://www.revbase.com/BBBMotor/TSb/DownloadPdf?id=42062

 

 

Section 10-00: Fuel System, Service
1996 F-150, F-250, F-350, F-Super Duty and Bronco Workshop Manual
 

SPECIFICATIONS
 

 

SPECIFICATIONS 

FUEL PRESSURE SPECIFICATIONS
Engine Condition 4.9L 5.0L 5.8L 7.3L 7.5L Engine Running 45-60 psi
310-415 kPa 30-45 psi
210-310 kPa 30-45 psi
210-310 kPa 41-55 psi
283-379 kPa 30-45 psi
210-310 kPa Key ON Engine OFF 50-60 psi
345-415 kPa 35-45 psi
240-310 kPa 35-45 psi
240-310 kPa — 35-45 psi
240-310 kPa

This is what I know now the new pump seems to have solved the problem, I do know that we can still by pulling the coil wire make the motor spin over about 20 times and the plus from the injector will still turn itself off??? Anyway thanks for the help and we will see how it goes.

Thanks for the info George.

I still don't understand how a fuel pump corrects a problem of fading ground signals to the injectors.

If anyone has insight to explain this please post.

Thanks again George, hope your problem is solved for good.

yo,

I've been looking for more info on the "injector pulse loss" causess and found this from Ford;

"...If a single cylinder is determined to be consistently misfiring in excess of the catalyst damage criteria, the fuel injector to that cylinder may be shut off for 30 seconds to prevent catalyst damage. Up to two cylinders may be disabled at the same time. This fuel shut-off feature is used on many 8-cylinder engine and some 6-cylinder engines. It is never used on a 4-cylinder engine. After 30 seconds, the injector is re-enabled. If misfire on that cylinder is again detected after 200 revs (about 5 to 10 seconds), the fuel injector will be shut off again and the process will repeat until the misfire is no longer present. Note that ignition coil primary circuit failures  will trigger the same type of fuel injector disablement...

If an ignition coil primary circuit failure is detected for a single cylinder or coil pair, the fuel injector to that cylinder or cylinder pair will be shut off for 30 seconds to prevent catalyst damage. Up to two cylinders may be disabled at the same time on 6 and 8 cylinder engines and one cylinder is disabled on 4 cylinder engines. After 30 seconds, the injector is re-enabled. If an ignition coil primary circuit failure is again detected, (about 0.10 seconds), the fuel injector will be shut off again and the process will repeat until the fault is no longer present. Note that engine misfire can trigger the same type of fuel injector disablement..."