Bronco dies on occasion.

I have an intermittent problem with my 5.8L 1991 Bronco that I need some ideas on.

Drive it for a while and it shuts off, no warning, sometimes when idling, sometimes when on the gas. 

There is no hesitation or rough idle before it craps, just shuts off like the key was turned.

Will not restart without first turning the key all the way off. Then it starts right up every time as if nothing were wrong.

Once again, it I try to pop it into neutral and restart, it will not restart, just turns over. If I pull over, turn the key off and then start. It comes on just fine.
 
I have new:

ignition switch, distributor, rotor, cap, TFI module, fixed old electrolytic caps in the computer that were bad, new battery, alternator, IAC, solenoid, EGR valve, Throttle position sensor is good, new relays, fuel pressure is good, new vacuum lines, 5 year old coil but it seems to be outputting good and input signal/connection is solid.

Hot/cold doesn't matter.

Pulled codes and only get 11, systems checks OK.

Done every line, hose wiggle test I can think of looking for intermittent shorts.

I'm about ready to surrender.

Any ideas?

What brand ignition module did you use ?

Masterpro I believe. I had the problem before changing the module however so I would doubt that the same exact symptoms would be present. The old one measured out OK actually but I decided to change it just in case.

You went though my list already.  Since you haven't changed the coil, that is suspect.

>-

Hey Mad,

Do you know if there is spark or no spark when it won't start?

If there is spark, I would suspect the fuel pump relay.  I had a very similar experience with a vehicle.  Thought it was ignition, ended up being fuel...a relay that would open when it got hot.

I will test the spark next time it happens though and see if maybe there is something wire related going on there. Did not test that. I guess that the relay could require reseting thus the no start without turning it all the way off. I did replace the fuel pump relay as part of a "huck a bunch of parts at the sucka" and see if it floats but maybe there is something in the wiring to that which could be an issue.

Do you think that an intermittent fuel pump would do this? I would expect that if it shut off totally that it would stutter a bit before cutting out but I could be wrong.

yo M,

btw, did you o the KOER portion of Self Test?

when it shuts down & you attempt to re-start but can't and engine is cranked over, do you smell gas?

Ford Ignition Coil Test No Spark No Start Tests

http://troubleshootmyvehicle.com/ford/4.9L-5.0L-5.8L/how-to-test-the-ignition-coil-1

uhhhh, the EGR tube should not be two pieces that just slide together should they ( I think it should not be ).

If they are, it is a **** poor fit that would let air out all over the place. If they are not, I might have found a problem.

Not sure it would cause the stopping problem or not.

When I crank the engine after the stop, I don't smell gas. It is fuel injected so I don't ever really smell gas…should I?

I know on my carbonated boat engine I will smell gas if it is not sparking but I expect that.

The KOER test is fine too.

replaced broken EGR tube. Idle is much nicer and not going up and down like it used to. I was having some rough idle in the dreaded 1500-2000 range that seems to be gone.

However while letting it run today to allow the computer to relearn the settings. I had the thing shut off.

Any ideas good test jigs or ideas on how to test for spark when you are solo and don't have someone to turn it over for you?

Another possibility on intermittent problems is the battery ground connection or the cable itself.  Remove it clean the connections and surfaces where connections are made.   Check the area  where the lugs attach to the cable, if there is any corrosion, replace the cable.  It would be a good idea to check all ground connections. ie. the computer ground

>-

I was able to discern that there was no spark after it shuts off.

1. start it up, runs fine.

2. engine shuts off, now after about 5 minutes of idle so thankfully it is reproducable.

3. try to turn key from ON position to restart, no spark at output of coil (it was late last night so I didn't trace circuits back to the ICM and distributor).

4. turn key off and then restart, powers up fine.

I did new battery cables early on. I cleaned up the contact surface on the engine block when doing this so the ground should be good. I need to check it to the computer however. I believe that the chassis of the computer is ground itself but not 100% sure. I have been trying to find a real schematic of the computer and can't find one anywhere. Even the pinout of the 8061 CPU is impossible to find and the pinout of the 60 pin connector for my year is not available. I might end up making my own schematic of it at some point…or at least the path from the chips to the ignition circuits. I was a chip level computer repair tech for many years so I am fine poking around in there. I will probably do some heatgun/freeze spray tests after I do the full ignition circuit tests again to see if it is a thermal thing. 

You may find an EVTM on eBay for your year Bronco.  Also, you can often find a complete set of service manuals for round $100.00.  Even if there is not one listed now, contact one of the sellers who specialize in old manuals..I think that meisk5 has a location that sells the manuals on CD.

Good luck,

>-

yo M,

1991 Bronco F Series Electrical & Vacuum Troubleshooting Manual

Price: $40.00 In Stock - Reproduction of Original Publication

Pkg Qty: 1

(English, Paper, FPS1212991)

http://www.helminc.com/helm/Result.asp?Style=helm&Mfg=FMC&Make=FRD&Model=BRON&Year=1991&Category=&Keyword=&Module=&selected%5Fmedia=

Written by Ford Motor Company, this book has the most in-depth wiring diagrams available. Included are circuit schematics, power distribution schematics, ground distribution schematics and component locations to accurately repair electrical problems . ETMS are model and model year specific, and their schematics are far more detailed than the wiring diagrams in the Service Manual. For best repair results, use this manual in conjunction with the Service Manual.

Description:

Diagrams With Component Location Illustrations Circuit Descriptions And Troubleshooting Hints.

Helm is Ford's official Publisher

---

How to Troubleshoot a No Start (Ford 4.9L, 5.0L, 5.8L)

http://troubleshootmyvehicle.com/ford/4.9L-5.0L-5.8L/how-to-troubleshoot-a-no-start-1

EXCERTS;

when it comes to a cranks but does not start problem, is the ignition system.

So my recommendation is to test for spark right off the bat to see if spark is missing from the mix (air, fuel and spark).

The idea behind checking for spark is to see if all of the 8 engine cylinders are getting spark. Let's assume that you have already tested for spark and you observed one of the following spark test results:

CASE 1: Spark was present in all of the cylinders A spark result, if you're using a dedicated spark tester, tells you that:

•That the ignition control module is OK.

•That the PIP (Profile Ignition Pickup) sensor is OK.

•That the ignition coil is doing dandy.

•You don't have to spend any time testing them or any money replacing them.

So, if you do have spark, the next step in your troubleshooting is to verify fuel pressure

Thanks for the link. Just ordered that manual. I have the other two shop manuals and the Haynes so now I can start a library.

Until it arrives, I'm diving back into the computer.

Hey Mad,

I like that you are able to be patient and really get into this.

Knowing that it's ignition now, have you connected a test light between the + and - terminals of the coil and cranked the engine?  If the light flashes, the primary circuit is good,  (No spark means you need a new coil.)

No flashing light indicates that there is a problem in the primary circuit. ( you will have to dig deep to find out if it's module, pickup, wiring computer...UGH!)

You won't find a schematic of the comp itself because a lot of that is secret stuff the car manufacturers don't want to reveal.

Good Luck and thanks for keeping us up to date.

I did a full test of the PIP, Spout, Ignition control line, etc. line last night. All are fine. 

Just for laughs I'm going to measure the fuel pressure again tomorrow and see if it fluctuates right before it dies. It could be an intermittent in the relay or fuel pump (relay was replaced and filter changed already)…..but I still think it is in the computer.

Tomorrow I will also pull the computer and attack it with a heat gun and freeze spray. I'll also try to trace the pins from port where all things ignition related go and see if I can do some circuit testing. If the digital logic is buffered with some transistors (some big ones with heat sinks on the side of the case) then one of those could be temp sensitive or have a bad solder or broken lead.

I bought this Bronco new in 1991 and really like it. I have a new Nissan Armada and it is OK but I enjoy my Bronco more. It is worth it to me to chuck parts and spend some time with it.

For laughs I decided to put in a new Idle control valve and a coil ( got a ICV code on a test this morning but it probably kicked it out when the engine died). Didn't do it.

Also put on a fuel pressure gauge and drove around to see if it was fluctuating before it died. I this a few months back but decided to check again just in case.

I pulled the ECM and tried to start looking up parts and following traces but they used a bunch of non-standard components (probably standard parts but re-labled so you can't source them or find data sheets on them) They did this for all chips and transistors. Also the rubberized covering that they dipped it in makes it very difficult to do continuity testing so I think I am stuck looking at getting a new ECM.

Received the new ECM. Also got the electrical/vacuum manual.

It is a newer model than was on my truck before. This one is a 3 digit code computer and my old one was a 2 digit.

I still have the engine stops running issue so the ECM was not it. 

I got a couple of codes after the stalls:

KOEO codes were:

Ignition TACH signal was erratic (module/wiring) or SPOUT circuit fault – Ignition Systems

Solenoid/circuit failure – shift solenoid 2 – Transmissions

KOER codes were:

Idle speed system not controlling idle properly (generally idle too high) – ISC

Knock sensor not tested (ignore if not pinging) – KS

Now I don't have an engine knock at all so I will do as they say and ignore it.

The transmission shifts fine when it is running so I'm not sure if the 622 means anything or if the new computer has a problem.

The 212 and 411 codes are troublesome.

The only things that are not new now are the distributor (but it was actually changed by a mechanic a while back).

When I was testing the SPOUT signal was good as were all signals from the ICM. I will probably pull all the covering off the wiring to check the connections from the ICM all the way to the computer.

Any ideas about the 622 code? Could something with the transmission be causing the shut down?