I have a 1988 F150, 2WD, AOD Automatic, with a single gas tank. It has a 302cid (VIN "N").

It had run perfect up to this point. I went to start it this morning to warm it up, and it stalled after 3 minutes. I went to restart it, and it refused to start. I let it sit a while, tried it again, and it started, ran for 3 minutes, and stalled. The computer had been suspect for a couple of things in the past, and after checking several things, including getting trouble codes, I replaced the computer. The intial codes were: 11 (system pass, Key on, engine off)

13 - Controlled idle out of range
18 - Spark output signal (SPOUT circuit fault) OR Erratic IDM, ECM, SPOUT circuit fault OR no tach signal to ECM
41 - System running lean

When I installed the new computer, it would not start. It would act like it was going to start, but when the key was released, there was nothing. Just out of curiosity, I pressed on the accelerator while turning the key (I know, shouldn't do this with EFI), and it would actually rev and run real rough, but when I released the key, there was again, nothing. After several attempts, I put the scanner on it, and got code 11 (system pass, Key on, engine off). I also got three trouble codes from the continous memory:

18 - Spark output signal (SPOUT circuit fault) OR Erratic IDM, ECM, SPOUT circuit fault OR no tach signal to ECM
53 - Throttle position sensor above maximum voltage
87 - Primary fuel pump circuit failure

I checked the fuel pumps (frame mount and tank), and both operate. The fuel injectors are firing properly, I have good spark, and the fuel filter isn't that old. I checked for fuel pressure on the fuel rail, and it squirted out a little. It gushed when the engine was cranked. Idle air control valve is in the proper range. I haven't checked the throttle position sensor yet.

The truck has 158,000 miles on it, and this is the first problem it has ever had (other than a dead battery once).

Any ideas? This is my only vehicle, and I have no way to work or the fire department (I volunteer)!!!

 

You need to use a gauge to check fuel pressure,it should be 35-40 and hold pressure.A squirt/gushed is not a valid test.You don't need much pressure to squirt yourself in the eye(CAUTION)from the Shrader valve.

 

Have you checked the timing? Sounds like it might have jumped time. Lot of miles plastic gear.

 

Temperature sensitivitity, starts and dies, and code 18 are all consistent with problems with the TFI, Hall Effect pickup, or wiring harness.

Check to see if you are losing spark. IF there is no spark, figure out why not. If there appears to be spark during crank, try disconnecting the SPOUT connector as a test to see if the engine will start and run. There are some failure modes where the computer can interfere with the TFI, disconnecting SPOUT will isolate the ignition system from the computer.

 

Ok, here's what I did so far. Just on a hunch, I went to attempt starting it this morning, and it started! Ran perfectly, and I was so thrilled! Then, just like yesterday, it died suddenly after about a minute. Refuses to restart, though it acts like it wants to. I disconnected the SPOUT connector, no change -- still getting spark though. Completely disconnected the distributor harness (leaving only the plug wires hooked up), nothing -- didn't even act like it wanted to start (I expected this, but tried it anyway). Hooked everything back up, still nothing other than acting like it wanted to start. Obtained the codes, and the KOEO was 11, and the Continuous memory had code 18 again.

Timing is quite a challenge to check without a running engine. However, when it did run for that short time, it ran perfectly. In fact, even better than with the old computer, so at least the timing advance commands from the computer to the distributor are happening.

When it does run, it runs for about a 30 seconds to a minute, then cuts off dead while it is still running in the initial warm-up mode. No sputter or anything. Sort of like turning off a water faucet or a light switch: Now you go it, now you don't.

Done. Fuel pressure is normal.

Thanks for the replies, looking forward to hearing more!

 

The computer gets two signals back from the TFI module. One is PIP, the other is IDM.

(Profile Ignition Pickup, Ignition Diagnostic Monitor)

PIP is the low voltage output from the Hall effect pickup. The computer uses this to determine when to fire the injectors. If the computer does not get PIP, it will not fire the injectors and the engine will shut down immediately.

PIP is also used internally by the TFI to determine when to fire the coil. If PIP is lost completely, you won't have spark. But it may be that PIP is OK for the TFI, but not reaching the computer. In this case you will have spark, but no fuel to the cylinders. This may be due to bad grounds, chafed or internally damaged wiring harness, weak TFI or Hall effect module, or corrosion at the 60 pin connector.

IDM is basically the same as the "tach" signal, which is the negative side of the coil primary. The negative side of the coil primary is shunted to ground by the TFI module to charge the coil, and then released to cause a spark. The tach signal goes (where else) to your tach, and also to a 22K ohm resistor buried in the wiring harness. The other side of the resistor is the IDM signal, and this goes to the computer.

So far as I can tell, the only use for the IDM signal is for posting/not posting code 18. It is fairly easy to break the resistor if you manhandle the harness. When this happened to me, I got code 18 but no other ill effects.

So I know from personal experience that code 18 gets posted if the computer gets PIP but not IDM. In this case the engine still runs. I conjecture that code 18 may also get posted if the computer gets IDM but not PIP. In this case the truck would shut down, but you would get the "hint" of code 18.

Tracing the PIP signal through the wiring harness is a little trickier than some of the other signals. You need a high impedance test light because it is a fairly weak signal. You need a test light instead of a voltmeter because of the alternating current nature of the signal. You could try removing the connectors on each end, slapping an ohmeter on the 60 pin connector, and back at the TFI module connector, and see if the PIP wire has a low resistance (less than 5 ohms). Inspect for corrosion at either end.

As I said before, it is important to check all of the ground connections. Battery cable, frame, block, post on radiator support, computer ground at firewall. PIP is a relatively low level signal and somewhat sensitive to ground shifts. (To attempt to deal with this, Ford supplies an "ignition ground" in the harness running from the TFI back to the computer. This does NOT supply ground to the TFI, but rather provides a reference level for PIP. The actual TFI ground for a side mounted TFI module is through the distributor body. For a fender mounted TFI, it is through the fender.

There is also a foil shield around PIP. This is grounded at each end and intended to avoid noise riding in on PIP. It is hard to say how necessary this is -- but the shield has been known to cut into the wires it surrounds, and create intermittant short circuits.

 

fefarms, I fiddled around with the harness that attatches to the distributor a little, and found something interesting. On a hunch, I checked for continuity between that foil insulator and the connector, and there was continuity on three of the six contacts. I'm assuming that this isn't normal. Should there be any continuity with any of the contacts? At the end of your last post, you mentioned that this is supposed to be grounded at both ends. How/where does it ground at the distributor end?


Don't know if you can see the pic here or not, but if you can, the continuity is between the 3rd, 4th, and 5th contacts from the left.

Just to rule it out, I also replaced the ignition switch on the advice of a friend of mine who is a mechanic (who is also stumped).

 

Call me a liar. The shielding foil is grounded to the EEC case ground at the computer end, not at the TFI end. I must have been thinking of how I would have done it, not how Ford did it.

Continuity is a slippery thing. It depends on what instrument you are measuring with and what is connected to the wires in question. If everything is connected, and the key is off, you would expect a low resistance (< 2 ohms) between IGN GND and the foil. You would expect a low resistance (< 10 ohms?) between TACH and the foil (backflow through the ignition coil). You would expect a low resistance (<10 ohms) between TFI PWR and the foil (same reason). I'm not sure about the "START" signal -- it depends on what else is connected to it. You would not expect to see a low resistance to PIP or SPOUT, but you still might read these as "connectivity" depending on whether you are using a digital VOM or a test light.

The best way to get an unambiguous test of the foil is to disconnect the TFI, the computer, and the ignition coil. Check PIP and SPOUT in the harness for connectivity to the foil. These are the ones that really matter. You can check "TACH" under these circumstances, and the resistance should now be fairly high (>100 ohms).

I can think of two more tests for you.

Clear all the continuous memory codes. Disconnect the battery or pull the STI jumper while codes are flashing out. Try starting the truck (the next time it is willing), and shutting it down with the key BEFORE it dies by itself. 10 seconds of running should be enough. Now collect codes from the PCM. Is code 18 posted? If it is, the code 18 may be a side issue not related to your problem. If it is not, then we have an indication that the computer may be telling us that it is losing spark.

The next time it shuts down and refuses to start, try inducing some ether into the intake. Will the engine fire on the spark you say is present, and the starting fluid you spray in? We are trying to confirm that everything is OK, but the computer (for whatever reason) is choosing not to open the injectors.

 

I have just a standard $20 digital volt/Ohmmeter. The Ommeter settings range from 200/ to 20M/. On the 200/ setting, it produces a beep and shows a number, which in my case was 35.00. The three that showed (sounded) continuity were the one that goes from the TFI connector to the computer, one that goes to a small connector hooked to the side it the ignition module, and one that goes right to the ignition. None of these appear to ge ground wires of any kind, other than the foil and bare grounding wire.

I could not get it to run at all since yesterday morning, though it still tries. I did think of the idea of clearing the codes and shutting it off before it stalls, but I though of it after it ran yesterday. I do have TACH signal, at least to the tachometer in the dash.

I did check the injector pulse with a noid light, and they fire correctly as long as the starter is engaged. I haven't tried the ether yet, but I will. I still have spark, but only while the key is turned in the "Start" position. As soon as I let go of the key, no run, no spark, no injector pulse. I can smell a little fuel after I do this. I can even rev a little as long as the starter is cranking(not good for starter, I know ). When I rev (less than 2000 rpm) there is black smoke from the exhaust.

 

Try the following tests:

With the engine in its not-running mode:

Connect the noid light. Disconnect the TFI connector at the distributor. Crank the engine. Does the noid light flash? I believe the answer should be "no". According to the Chas. Probst book, the computer must get PIP during crank to fire the injectors. I am trying to confirm this. If the noid light does flash even without PIP, we need to take a different direction.

Reconnect the TFI. Crank the engine with the throttle held to the floor. Does the noid light flash? It should not, because the computer should go into "clear flood" mode. If it does flash, the TPS may be faulty.

Reconnect the TPS, and disconnect the electrical connector to the MAP sensor. Try starting it now. According to the Probst book, the MAP sensor is ignored during crank, but is used during cold warmup. If the MAP sensor is giving an impossible rich reading, the truck may flood out immediately when the computer tries to switch from "crank" to run. By disconnecting the sensor, I'm hoping to push the computer into "failure mode effects management", wherein it should substitute a value derived from TPS for the MAP sensor.

Reconnect the MAP sensor and disconnect the TPS. Again try to start. See if that helps.

The question we are trying to answer is whether we are losing PIP to the computer, and whether this is causing the stall, or whether the loss of PIP is merely a consequence of the engine stopping for some other reason.

Use your voltmeter. Remove the TFI connector. Turn the key to "on". Probe for +12 volts at the "TFI Power" pin on the TFI connector. There is another pin on the TFI called "Start" (ostensibly used to control dwell) that may also have the side effect of providing power during crank, but the TFI is losing power when the key is released.

 

Thank you so much for your time and patience. I don't know if you guys use the reputation system (those little green things that show up next to ypur post count) here, but I sent one your way. I also sent some to the others that responded to this thread. It may not count since I'm a newbie, but anyway...

I got a hold of some starting fluid and tried to see if it would run off of it, and it wouldn't. Apparently the spark cuts off when I let go of the key.

I connected the noid light, disconnected the TFI and cranked, no flash. Reconnected the TFI, cranked, and the light flashed. I swapped out the TPS for a new one. Did the above again, same result.

Tried the tests involving the MAP as you described above, to no avail.

The TFI has power to it with the key on.

I'm wondering if maybe the problem is with the TFI module itself or a fusible link somewhere. Possibility, given the symptoms and results so far?

Parts added to this point are ignition switch, computer, and TPS sensor. I have also inspected every inch of the harness from the TFI to the computer connection, and no worn wires/shorts. I swapped out a few connectors that I thought might be troublesome with identical parts. Someone suggested that I check the fuses as well. I didn't think there were any fuses in the fuse panel for the fuel injection or the TFI, but I tested all of them anyway, and there were no bad fuses.

Again, thank you very much for your time and patience -- it is very much appreciated!

 

It is possible the TFI works OK when the battery voltage drops during crank, but quits as soon as the starter load drops away (and the battery voltage rises again). That would explain your code 18. The TFI has been known to be temperature sensitive -- that would explain your "runs for one minute and quits" and kind of also goes with "works in crank, but not in run", since it will run hotter once the voltage goes back up.

The easiest way to check this out is to find a distributor from a different car or truck with the same engine. Swap out the whole dizzy, this will effect a change of both the TFI and the pickup coil. Or you can try swapping them one part at a time -- the TFI requires a special tool (or a ground-down socket) to remove. You pretty much have to pull the dizzy out to change the TFI on a 5.0 liter -- not enough room to get at the screws.

Changing the Hall Effect pickup requires removing the distributor drive gear from the shaft. It is pressed in place. You can get it off with a soft-face hammer and a vise, but it is tricky to do so without damaging anything. Easier to buy a rebuilt distributor with the pickup already in place -- only costs ~$40 more than the module itself. Just make sure you get a cast iron distributor gear.

 

She Lives!!!



Thank you again for your time and knowledge! It has certainly been an educational experience!

 

Glad you got if fixed. I feel like my first and last posts were on the mark, and we got into somewhat of a wild goose chase in the middle. I think both of us got the idea the TFI was OK because you always had spark during crank. Usually a failing TFI will lose spark completely and won't fire at all until it cools off. Your history with this is a good lesson not to extend "usually" to "always".

 

The "wild goose chase" had it advantages, though -- replaced a few parts in the process that may have needed changing eventually! At least I know now that should code 18 show up again that I should start with the TFI.

After doing some searching on Google, I found that the TFI module is notorious for causing odd problems like this. In fact, there was even a class-action lawsuit over the little thing. Certainly, I coouldn't see why someone wouold sue over sich a thing, unless it caused fires or injuries/death, but I can't understand a lot of what some people do.

This truck has been by far the most reliable vehicle I have ever owned -- it has never left me stranded -- well, it did, but it was in the driveway, so that doesn't count!

Anyway, thanks again!