i have a 92 bronco w/351w. i started havin erratic idle probs and the check engine light came on, so i parked it and started doin some work on it, i replaced the parts that the haynes manual said would cause the prob, tps, map sensor, idle air control valve, but no luck. it actually made it worse. i also did a tune-up, the whole works including replacing the fuel filter, it got a little better but still no luck. i decided to take to take it to a guy i now that works on fords everyday and he has had it for 3 months now and he cant figure it out. he has replaced the fuel pump and a piece on the exhaust (the small pipe that is located between the O2 sensor and the catalytic converter that runs up the firewall to the back side of the engine). he has also replaced the 'puter in it and that didnt help. he is tellin me that there is an electrical prob and said that he had a tester to check every wire in the main harness, but found nothing. once he hooked the harness back up, it wouldnt even start now. he told me that it might have burnt up a module and he said he was gonna replace it. it is my beach buddy and i want it back, can "ANYONE HELP", thanks.

Mark

 

Did you even try pulling the codes, the computer will tell you what the problem usually is when the check engine light turns on.

 

I just discovered, after several months of fiddling with my no-start 1990 Bronco, that there has been a well known, long standing problem with the TFI-IV ignition system. There have been lawsuits attempting to bring about a recall, which has apparently happened on a very limited basis...I'm not positive, but I think if you are over 100K miles, fogeddaboutit! There is some info in various threads, but you may want to google for more info...
So here is how I got my '90 Bronco running...I got the info from Haynes, and confirmed the details on FTE...then after lots of hoops, found the real answer on FTE...
Truck wouldn't start...no fuel pump sound on ignition...
1) replaced Fuel Pump Relay...no result...waste of time!
2)replaced EEC relay...waste of time
3)changed fuel filter...probably worthwhile, but no change...
4)check inertia switch...just fine...no diff...
5)check fuel circuit wiring...fine, still no fuel pump buzz on ignition...
6)replace ignition switch...waste of time, no diff
7)engine computer bad? Ordered replacement...gave up when Kragen didn't want to fill order at price matched by a NAPA store(simply canceled order...didn't bother to call!) Turned out ok, as that ultimately turned out to not be the problem...
8)replaced fuel pump...a big pain, as you must siphon out the gas, drop the fuel tank (bolts usually very stuck, corroded...hint, try spraying some sort of penetrant several days before)...maybe worthwhile after 100k miles, but was not the problem...so after spending a couple hundred bucks, and a lot of time and effort, what turned out to be the problem, NEVER listed in Haynes!!!!
THE TFI "Ignition Module", responsible for hundreds of thousands of sudden stops..."AAA, my Bronco (or F-150, etc., etc.) just died on the freeway (or at a stoplight, or when I was trying to pull my boat out of the lake...)""...you get towed to a shop, and maybe come to figure out many dollars later...it's the GD TFI!!! A problem Ford has left you hanging with!!!

Good news...A new unit costs about $50-90 depending on your parts store...it takes twenty minutes maybe to replace it...when I did it, my truck started right up (with all the old parts, except the fuel pump...to hard to put the original back!)...

So, try what I didn't know first...replace the TFI "ignition control module" FIRST!!!

 

So I am assuming that the standard self tests turned up nothing before the computer and all of those sensors were replaced. Because, the KOEO and KOER tests are designed to pinpoint problem areas and give an indication of the location of the problem BEFORE you end up replacing a bunch of things that aren't the real cause.

I gotta be honest, it sounds like he's chasing ghosts rather than real problems. Any Ford mech worth his salt would pull EEC codes FIRST before replacing anything. Its SOP (standard operating procedure) on EEC drivetrains. I find it impossible to believe that with a "check engine" light ON that there were NO trouble codes in the KOEO test. The CEL only comes on when a code is generated! Even if the KOEO comes back negative the KOER will turn up anything else.

Since it won't start, whatever has been done could well have killed the TFI module (ignition module) which can cause a "no start" condition. Running electrical tests requires that sensors and modules be disconnected prior to testing to avoid shorting them out. After three months and a truck in worse shape than when you sent it to him, I'd get it away from him QUICK. Just my personal take on the situation. If you can get it to start, run the KOEO and KOER self tests and see what codes you get.

www.fordfuelinjection.com is a very good resource for information and assistance when troubleshooting and running these tests.

farklevill,

If you had run the KOEO and/or KOER tests FIRST, you would have, at the very least, gotten a code 18 which indicates a failed SPOUT/Tach signal from the TFI module. Its a good bet that with a code 18, the TFI module is the culprit. Ford moved the TFI module in mid/late 1991 from the distributor lower casting to a large heat sink on the driver's inner fender to reduce the number of heat related failures. This maneuver was enough to satisfy the "legal eagles" to the point where any suit didn't stand much of a chance.

 

The "computer", such as it is, will often give less than definitive information. In the case of my TFI problem, there were no codes! So, while codes might help, don't rely on them completely...often sensors are bad (Garbage In, Garbage Out!)...or the system is just not mart enough to give you the full picture...

 

The EEC system monitors the sensors! If they go bad, the system detects an "out of range" reading from the faulty sensor. This is why ALL of the sensors are fed power directly ALL the time. The computer can detect a LOSS of voltage but cannot detect the presensce of voltage. This is why the ground on each sensor is monitored not the power feed. This way if the power feed becomes weak (not totally gone but not the "expected voltage"), so does the voltage going to ground and in turn the EEC computer can (and does) detect lower than normal readings. I'm not saying the codes are the "end all" answer but running BOTH tests BEFORE guessing will certianly help determine what is NOT the problem. I realize in the case of a "no start" its impossible to run the KOER test. The system doesn't need to be smart enough to give you the full picture. The parameters and toleracnes that EEC drivetrains run under are so tight that one bad sensor or ground etc. can be enough to affect multiple aspects of the entire drivetrain. Example: A bad EGR valve or EVP sensor can ultimately cause shift problems in the E4OD transmission. You may or may not notice any major difference in engine performance but push the EVP snesor just enough out of range and it can give you a 1-2 shift anomally. So, no, the EEC computer won't tell you all that, but you can bet that replacing a bad EVP will magically fix the 1-2 shift anomally that began about the same time.

 

Grey, thanks for the info, now and in the past. I'm not dissing the code route...it is definitely the best way to start. My main point is that the no-start drill at some point hits the question of whether the fuel pump is running, either at initial ignition (the reassuring 1-2 second buzz)or after...the line of logic goes from one point to the next along the fuel system electrical circuit, which I followed. What does not seem to be common knowledge is that a malfunctioning TFI can cut off that power (you tell me where!) before it works its way down (pump relay, inertia switch, pump, etc.) the circuit...the fuel pump circuit can be in perfect working condition, but seemingly be the cause of the no-start...I do have another question for you...the wiring harness to the distributor has one branch that goes to the TFI, and another that goes to what appears to be a sensor, attaching a few inches to the left of the TFI...I heard a mechanic refer to it as the "stop"something...apparently used to short the timing circuit, so it can be recalibrated...any info on that? Thanks again!
Fark (aka farklevill)

 

Oops, I mean the "sensor" is to the right...mine has come loose (the harness) and I can't see how it is supposed to attach...the distributor base has a screw, but I see notheing on the harness for it to attach to...

 

so your saying the truck had no spark and still did not throw a code?????

If you use the OBD correctly and also the testing procedures in the Haynes....Mitchel....or a good quality Ford service CD for your year/model you would have saved yourself a boat load of time and money.

In a no start condition one of the very first things I would have check would have been the spark