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1988 5.0L 2WD - thermostat lower-temperature consequences to EGR, PCM functioning

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1988 5.0L 2WD - thermostat lower-temperature consequences to EGR, PCM functioning

Old 01-18-2012
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Default 1988 5.0L 2WD - thermostat lower-temperature consequences to EGR, PCM functioning

I have a 1988 F150 with 5.0L engine. It has electronic fuel injection and EEC-IV electronic engine controls.

I have a couple of questions. One regards fan-clutch and water-pump wear, and the other regards EGR functioning and the check-engine light, and these questions seem like they could be interrelated because I have been using a thermostat with a lower-than-OE opening-temperature rating when the engine's computer may be assuming I have a thermostat installed with the original-equipment (OE) temperature rating. The OE temperature rating is apparently 192 deg F or 195 deg F, depending on what parts store I ask, and I am using a 180 deg F thermostat.

I am posting the questions separately in the interest of keeping each question as brief as possible.

The first question regarded fan-clutch and water-pump wear and was posted here.

Second question: Does a thermostat with a lower than OE opening-temperature rating cause the on-board engine-control computer to miscalculate the proper amount of EGR?

I was once advised by a auto-parts store employee that I should probably use a thermostat with lower-than-OE rating under the theory that an older engine will run better with less trouble if it has a thermostat with a cooler opening-temperature rating than the original equipment. A 180 deg F thermostat was suggested.

At first I was reluctant to change to a cooler thermostat. But I eventually decided the auto-parts guy was more likely right than not. (By the way, I would appreciate any comments to clarify whether the auto-parts guy was indeed right.)

So about 2.5 years ago I installed a 180 deg F rated thermostat.

As a result the temperature gauge climbs up only half way to the bottom end of the “normal” range.

(By the way, I had also replaced the regular radiator with a heavy-duty radiator a little over 3.5 years ago.)

During at least the last few months my check-engine light has been flickering occasionally in a somewhat erratic manner but then would usually go off for extended periods of time. Since my battery charging light would also occasionally flicker in the same manner, and since an independent test of the battery and alternator would confirm they are functioning properly, I figured the flickering lamps were perhaps due to something like an aging resistor in the electronic display circuits.

However, I had a smog test done recently on the truck. Part of the preparation for the test involved running the engine at a rather high rpm for an extended period of time. (I suppose the intent was to burn out any carbon that may have accumulated in the combustion chambers.)

But one thing that has been very noticeable since the smog test is that the check-engine light doesn't just occasionally flicker. It now flashes on and off, on frequent occasions, especially when I am accelerating. Usually the light will go off when let up on the gas peddle and accelerate more slowly.

So I finally decided to read the engine's diagnostic trouble codes. Here are the results:

Key-on, engine-off (KOEO):

code 32 = EVP voltage below closed limit
code 67 = Neutral Drive Switch (NDS) circuit open (= Neutral/drive switch open or A/C on, per Chilton manual)

“Continuous”:

code 32 = EVP voltage below closed limit
code 29 = Insufficient input from vehicle speed sensor

I don't know what to make of the codes 67 and 29, but I figure that the code 32 is probably what is causing the check-engine light to flash.

Anyway, it occurs to me that, because of the 180 deg F thermostat, the engine-control computer may be assuming that the coolant temperature is too low and therefore may be trying to make the engine to run hotter, and, as a result, may be closing down the EGR in order to accomplish that purpose.

So I wonder if the engine is working against itself and causing temperatures to be more extreme than normal: The coolant is cooler than normal, but maybe, as a result, the combustion chambers are also hotter than normal.

I noticed that my driver's-side exhaust manifold is cracked around its circumference at the back end of the manifold, and I wonder if this could be caused by the supposedly higher extremes in temperature, especially the supposedly hotter exhaust gases due to the supposed shutting down of the EGR because of the cooler coolant.

I recently bought a vacuum hand-pump/gauge and I already have a digital volt/ohm meter, but before I go about doing the testing recommended by the Haynes manual and potentially damaging connectors and/or brittle vacuum lines, I wonder whether I should first replace the 180 deg F thermostat with a OE-rated thermostat.

Any insights would be welcome.

In particular, is my conjecture about the computer's EGR response to the cooler-than-normal coolant correct?

And should I first replace the thermostat with an OE-rated thermostat before risking diagnostic-testing damage to connectors and brittle vacuum lines?

I wonder if the “Insufficient input from vehicle speed sensor” (= trouble code 29) is also complicating the matter. I can find nothing in the Haynes manual about a “vehicle speed sensor”. What should I do about this trouble code?

I wonder if the “Neutral Drive Switch (NDS) circuit open” (= “Neutral/drive switch open or A/C on”) trouble code 67 could be due to the fact that the “P-R-N-O/D-D-1 pointer assembly with the tiny pointer-control cable has crumbled. (I do my gear-shift-lever shifting entirely by “feel” of the gear-shift lever with no visual feedback.) I keep the A/C switch off; the A/C system does not hold a refrigerant charge anyway.

Is there anything I should do about this trouble code 67?

This web page ( http://www.oldfuelinjection.com/index.php?p=47 ) says the code 67 means “Neutral safety circuit failure”. The word “safety” reminds me that I can sometimes start the engine in gear-shift positions other than “Park”. And a previous owner has also installed a starter push-button switch that connects directly to the starter relay under the hood because the OE ignition switch is sometimes hard to twist to the start the engine.

And if I install an OE thermostat and clear the trouble codes and if the “EVP voltage below closed limit” code 32 does not return (and no new trouble codes appear), do I still need to do electrical and vacuum diagnostic testing on the EGR system?

It may also be worth noting that the computer-controls description at
http://www.oldfuelinjection.com/
seems to say that the computer anticipates that sensor characteristics may vary (from one installed sensor to any alternative installed sensor) by as much as 15% and that the computer will calibrate such a sensor when it operates in system-learning mode, which occurs typically after the battery has been disconnected and reconnected.

This suggests that the computer may assume that the installed thermostat is an OE thermostat and that when the Engine Coolant Temperature Sensor (ECT) indicates to the computer that the engine temperature has leveled off, the computer may assume that the temperature is 192 deg F or 195 deg F rather than the actual temperature of about 180 deg F.

So, in summary, it seems that the computer may be working under the assumption that the warmed-up engine coolant temperature is 192 deg or 195 deg rather than the actual temperature of about 180 deg.

First of all, is this the way the computer works?

And second, what affect does this have on the general performance of the engine – for example, wear, gas consumption, trouble codes, etc.?
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Old 01-18-2012
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I'm not all that familiar with the 80's F-150's. If the fan clutch is bi-metal or silicone oil based, they operate under a predetermined temperature rating. I don't know if the 12 to 15F difference would be enough to cause that kind of wear and tear on your water pump, but I fan that has been damage sure can. A damage fan can cause vibration and subsequently cause undue wear on the water pump seals and bearings.

Dropping the temp rating of the T-Stat in order to increase engine longevity is a point of argument. Usually when dropping the T-Stat setting, there are other engine controls that should be changed/reprogrammed in order for all the components to work right...like fuel injection, egr, etc.
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Old 01-19-2012
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Thanks, Kevin, for the comment.

I did diagnostic testing of the EGR valve per Haynes manual.

EGR valve holds vacuum extremely well.

And it also ostensibly passed the functional test. In particular, I had to use several pieces of wood to simulate a helper's foot on the gas pedal for fast idle by bracing the gas pedal against the steering wheel to keep engine running while the Idle Air Control solenoid was disconnected and vacuum was applied to the EGR valve. The result: When vacuum was applied to EGR valve, engine slows down if cold, but if hot, gets erratically very uneven rpm.

With vacuum gauge attached to the EGR valve's vacuum hose, as the engine rpm was increased to a very fast idle, eventually (with increasing rpm) the vacuum gauge needle shows vacuum of sorts, but the needle jumps around erratically and very rapidly between zero and about 3 inch Hg.

This erratic behavior of of the needle was not mentioned by the Haynes manual; so I wonder: Does this erratic behavior indicate some sort of problem?

When I attempted to do the Engine Running Self-Test to check operation of the EVR solenoid, the self-test would not activate: Aside from a momentary flash of the the "check-engine" light as I turned the OE ignition switch from start position to run position, the "check-engine" light did not flash to indicate self-test operation. For actual starter operation I had to use a separately installed ad-hoc starter button that is connected directly to the under-hood starter relay; the OE start switch does not always turn the starter; sometimes it does; sometimes it doesn't; today it did not; I had to use the ad-hoc starter button. But I also turned the OE ignition switch to the start position simultaneously in case the engine computer was expecting that in order to start the self-test. Result: no flashing of the "check-engine" light to indicate self-test operation. When I turned the engine off and then turned the ignition switch back on, the KOEO self-test began and showed that there was indeed continuity in the self-test jumper hook-up.

So the Engine Running Self-Test would not start; it was needed to test proper activation of the EVR from the computer's control as would be indicated by a momentary vacuum of at least 1 inch Hg at the EGR valve's vacuum hose during the Engine Running Self-Test.

So I wonder whether the non-operation of the Engine Running Self-Test is due to the bum OE start switch (which is bypassed by the ad-hoc start switch). Or perhaps, is it due to a bum Neutral Drive Switch (NDS), as suggested by the code 67??
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Old 01-19-2012
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If you can get your hands on some electrical schematics, I think that might help. I suspect that NDS might have something to do with the engine running self-test.

I would test all vacuum lines and repair before you start down the bunny trail of EVP and EGR issues. A simple vacuum test is to use some carb and choke cleaner, start the truck and then spray the cleaner on each vacuum line, fitting and connection. If the idle increases, then that area has a leak and needs to be repaired.
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Old 01-20-2012
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Agreed. Vacuum leaks can mislead to other problems.
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Old 01-25-2012
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Default Problem resolution -- now, Nooooo Praaaahblem!

Since the RABS speed sensor (on the differential) seems likely not to be involved with engine management, and since my anti-lock brakes warning light has not been coming on while I'm driving, I figured that the code 29 might not come back if the I cleared the trouble codes. So I cleared the trouble codes (by disconnecting the self-test jumper while the ignition was on).

But it seems that simply clearing the trouble codes probably caused the EEC-IV module to re-learn the characteristics of -- and re-calibrate -- the EVP sensor.

Anyway, the "check engine" light has not been coming on when I am driving -- not even a flicker!

Nor has the anti-lock brakes warning light come on while I'm driving.

Moreover, the engine is running a little warmer. The temperature needle goes up to slightly under the bottom of the "normal" range, whereas it used to go only about half way up to the bottom of that range. (Recall that I have a 180F thermostat installed.)

So it seems the problem has been solved.

My guess is that maybe slow accumulation of carbon in the combustion chambers probably caused the engine to drift out of proper EEC-IV calibration; and then the burning off of the carbon at the smog test probably caused the engine to swing to a new out-of-calibration state.

See https://www.f150-forums.com/1987-1996-ford-f150-16/1988-5-0l-2wd-location-vehicle-speed-sensor-1240/ for related info.
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Old 01-25-2012
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Glad to hear that the problem has been solved Richard.
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