1987 Ford F150 5.0L V8.
Hi, I can't get active KOEO error 23 and CEL light to go away. I had just replaced the TPS again (after only 5 years!) due to hesitation on throttling up, active KOEO code 23 (fail self test), memory code 53 (TPS voltage above range), and multimeter test showing green-sensor wire at 2.5V (too high)vs ground with closed throttle. Now thats all fine, Red=5.0v vs ground, Green=0.75V vs ground with good smooth response to 4.5v on WOT, Ground=good continuity to battery. Also fixed the throttle hesitation issue. I had also pulled the neg battery cable for a good 30 min which cleared the memory codes. Not sure how to re-calibrate. I cycled the ignition key several times, cycled the throttle to WOT. Started and idled it for 15min and did a couple of WOT hits, drove all around for about an hour including freeway. Of course it went through its learning paces, started slow idle at 700 rpm and finally came up to 1100-1200 which seems high (doesn't reduce with pulling Air Intake bypass electrical). Runs quite nice and smooth over all, decent power for an old truck. Only OBDI KOEO code in memory is 11.

But...The CEL keeps lighting up and I get an active KOEO code 23 TPS fail self test. Nothing in memory (11). Since the new TPS checks out electronically, I'm confused what it can be. No, there isn't any way to twist it to bring the base green signal up to 1v on this model. Is there a procedure I am missing to calibrate? Is there something else that cause the puter to send this code? The only other thing that is bugging me is the idle RPM seems a tad high.

(btw, I had just replaced the timing chain, water pump, front main seal, re-sat the battery ground behind the smog pump, adjusted timing to 10 BTDS, replaced radiator, cleaned the throttle body, had replaced the AIC valve due to super high idle rpm, recently replaced alternator and added its own direct ground to battery, replaced ignition and fuel relays and some other stuff, almost there!)

 

Adding, I tried clearing presets again by first putting the ignition into KOEO and disconnecting battery for 10min, also at the time jumped the positive battery side to engine ground hoping to clear remaining capacitor power (old myth?) and let the motor go through a normal relearn cold start, idle, pumped WOT a few times and drove it once it settled down for 30min including highway. No stored codes but the CEL just won't go away and I'm still getting KOEOff code 29, and only 11's for stored code. At least the idle speed seems to have settled down to 1000rpm. Backprobing the TPS wit KOEOff still gives: Red vs grnd 5.0v, black ground 0v vs battery, green signal throttle closed=0.75v vs ground with smooth rise to 4.5v at WOT. Mystery for me.

 

A fault in the wires between the EEC & TPS can also set that code. But read these pages before doing anything else:

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Thanks Steve83. That service manual is a good thing to have. DL. I'll have to orient myself on the EEC terminal pins to test for continuity. Was interested in going to the eec to test the injectors anyway. With the first photo, are you suggesting too pull and take apart the eec to look for obvious trouble?

 

Yes. Often, it's bad enough to just smell near the e-brake pedal. IDK what you mean by "going to the eec to test the injectors". If the engine runs, the injectors work. That's the best test for them. But in ~40 years of working on these trucks & every other kind of vehicle, I've never found a bad injector unless it was crushed or burned.

 

Well that was an interesting exercise but the issue persists. At least I didn't seem to have done any harm. As per Steve83 information I did check continuity of the three TPS wires to the computer and across the connector to be sure, which were all good (and for good measure took some extra time to do the same for some other sensors, relays, AIC, EGR, MAP, a few other things =all good). I pulled the ECU and couldn't see any obvious issues. There's only one electrolytic capacitor on this thing 3.3uF 65V and it looked fine, no identifiable leakage, discoloration on the board, or swelling. I replaced it anyway with my rusty soldering skills. That clear coating took a bit to get off to expose the joints. The rest of the board looked great and eerily new appearing. BTW, I couldn't perform a resistance test on the old one as I damaged it trying to take it off. The truck started up normal and went through the learning paces fine, drives the same (pretty decent for an old truck) but it still didn't like the new TPS. Still throwing KOEO active code 23 and CEL light on. I dunno. Since the truck runs OK, don't have other ECU symptoms like constant fuel pump, and without a detailed diagnostic ECU testing rig, I'll have to conclude for now that its at least nominally functional. Perhaps the starting voltage of the TPS (0.7) is just lower than it will accept whereas the one I replaced was way to high (2.5v). Not a very satisfying explanation and I really don't like driving much with a CEL light on, can't just turn the radio up. "Oh just ignore that..". Maybe I'll have to keep my eye out for a swapable ECU. Also, maybe I should have actually recorded resistance values instead of just going with continuity tone, maybe a small drop from closed 0.7v is a problem?. Any ideas are much appreciated.

A further note regarding removing the ECU. It has been suggested to remove the wheel well for better access to the ECU wire harness bolt by some. No need. Just take off the cruise control throttle assembly and come in from the top.

 

Did you read about ratch on the TPS testing page?

 

Ya, and reread. But i'm not sure what to make of it in this case. My measurements of the TPS output voltage at closed throttle seem to be reasonably in spec and steady. If it wavers too much, I can't see it but I don't have a recording oscilloscope with a quick response time. I have to wonder on these old unsophisticated ECU's what their response time really is:>) Unlike obdII cars I don't have a way to read real-time PID values. At least I don't know of how. The OBDI code 23 I see is triggered at KOEOff, even just after 1st turn of key after reconnecting the battery, not a stored code or triggered after starting or throttle-up, its a self voltage test not a dynamic function test as far as I understand. So I'm not clear at all of how the "ratch" even comes into it in this case unless that is learned and set at KOEOff and somehow there is already a bad (but in range as measured) TPS signal with no throttle input?

As far as the plates go, these really are pretty good n tight and now very clean, again. Think I'm pretty good there or maybe I didn't understand what was written sufficiently.

One interesting point though from that writeup, after going through the relearn period with engine on and idling (starts at about 700rpm cold, a little rough) for five minutes or so with no foot on the gas, then up to a nice 1000rpm, then sometime after warmup, the idle does jump up a bit more than I like to 1200 or so and likes it there, particularly if I bump the throttle and let it settle. That might be consistent with it possibly going out of 'closed throttle mode' and staying there. Subsequent starts go right to 1200rpm. If I could monitor the TPS output voltage better over time, perhaps I'd catch some noise. I'm not getting any stored trouble codes such as for 'open throttle'. Dunno.

 

You don't need a scope - any decent digital multimeter is good enough, but one with an analog graph is best because it responds faster than the numerals. That's how you get "real-time" data about the TPS, as that linked page explains. Yes, ratch is dynamic because it's always learning. Yes, that page clearly says that it begins learning at KOEO. And the graph specifically shows the lowest & highest values that are "in-range".

The first few steps of the pinpoint diagnostic for code 23 are:

DH2: Service Code 23/121 indicates that the Throttle Position (TP) sensor's rotational setting may be out of Self-Test range.

Possible causes:
-- Binding throttle linkage.
-- TP sensor may not be seated properly (tightened down).
-- Damaged TP sensor.
-- Damaged processor.
l Visually inspect carburetor/throttle body and throttle linkage for binding or sticking.
l Verify the throttle linkage is at mechanical/closed throttle. Check for: binding throttle linkage, speed control linkage, vacuum line/electrical harness interference, etc.
l Does throttle move freely and return to closed throttle position?

Yes - GO to «DH3».
No - SERVICE as necessary. RERUN «Quick Test».

DH3: Service Code 53/123 indicates that the Throttle Position (TP) sensor signal is greater than the Self-Test maximum value.

Possible causes are:
-- TP sensor may not be seated properly (tightened down).
-- Damaged TP sensor.
-- Short to power in harness.
-- Damaged processor.

l Rerun Key On Engine Off Self-Test.
l Is Code 63 or 122 present (ignore all other codes)?

Yes - GO to «DH4».
No - GO to «DH6».

DH6: l Key off.
l TP sensor disconnected.
l Disconnect processor 60 pin connector. Inspect for damaged or pushed out pins, corrosion, loose wires, etc. Service as necessary.
l Install breakout box, leave processor disconnected.
l Measure resistance between Test Pin 47 and Test Pins 26 and 57 at the breakout box.
l Is each resistance greater than 10,000 ohms?

Yes - REPLACE processor. REMOVE breakout box. RECONNECT TP sensor. RERUN «Quick Test».
No - SERVICE short circuit. REMOVE breakout box. RECONNECT all components. RERUN «Quick Test».

Where it refers to a breakout box, you can just probe the wiring directly; either by carefully probing the connector terminals, or with pierce-probes in the wire.

 

Thanks steve83 for the further info. Ya I'd love a graphing multimeter....on the list as a needed item.

I can directly drop right down right down to 'DH6' on your list: throttle/throttlebody mechanically works perfectly, no codes 53,63, other. There obviously still could be something wrong with the brand new TPS but it does spec out by the usual multi-meter tests.

The pins on the ECU side all look fine and clean (with dielectric grease) as well as the harness side pin-holes. But a second look and clean can't hurt. I'll have to see how to borrow/rent a 60-pin breakout box. However, for a simple resistance tests mentioned above in DH6, any reason I can't just use simple connectors on those pins? I assume it refers to male pins on the ECU side correct? Probably would have been smarter to have done this testing when I just had it out, prior to replacing Caps, lol.

I could bench test the TPS, look for proper starting resistance and and change in resistance with turning the 'dial', but I'll have to find those specs. . The one it replaced definitely had issues as tested on the truck with codes 23, 53, 73 (engine running).