Throttle position sensor trouble

megan

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Aug 6, 2011
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Greetings!!

I have an 89 Bronco full size V8 5.0 xlt automatic and here is my story...

Rough idle at low speed/rpm. If I'm cruising at about 25mpr and my foot is not on the gas it chugga chugs. Also the brakes loose vacuum pressure. By disconnecting the tps problem solved, idles good and brakes are fine. Got a new tps put it on and problem persists. replaced the iac and that didnt help either. I have also cleaned the throttle body, egr valve, replaced gasket on upper intake manifold and repaired a broken vacuum tube. I have to make a 700 mile trip home in a week to Dallas(where it is stinkin hot) and not sure I want to make the trip with the tps disconnected. Maybe I got a defective new tps but I was hoping to get some advice before I by a new one or pay someone to test it for me.

Thanks in advance for any help or ideas.

Megan

 
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miesk5

96 Bronco 5.0
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yo Megan,

The brake issue and prob TPS as well could be cause by a vacuum leak.

I think I gave you a vac leak test before?

If not;

Leak Test; On an idling engine check for vacuum leaks using a mechanic's stethoscope with the probe removed, or a ~3' garden hose section. On COLD ENGINE only, use propane torch w/rubber hose attached, UNLIT or spray carb cleaner, when it gets to the the leak the RPMs will rise. Also check: vacuum hoses; intake manifold gasket & throttle body; PCV line; vacuum reservoirs: EGR Sys Vacuum Tank & 2ndry air (coffee can); AC, heater, defroster, vent control ckt & vacuum tank (plastic ball type), under dash & lines to heat/blend/etc. doors; power brake booster; cruise control ckt, etc. Where applicable; BEWARE OF BELTS/PULLEYS, FAN AND HOT ENGINE by miesk5 at Ford Bronco Zone Forums...

But first do a DIY Code test, by our pal here, Broncojoe at http://broncozone.com/topic/14269-code-reader/page__pid__74587__mode__threaded

heat the engine up; idle until temp gauge is in normal range you usually see

and wwhen it warms up; shift thru all gears incl Reverse anyway.

Then turn off all accessories/lights, etc.

Make sure A/C is off and transmission is in Park (automatic)

Do Key On Engine Off (KOEO) portion first.

Look Codes up in my broncolinks.com site using the new Search function if you have time to troubleshoot today.

And look @ TPS section @ http://www.broncolinks.com/index.php?index=137

And Post em here according to

KOEO

& KOER

Test, Operational Description & Parameters

Source: by Ryan M (Fireguy50) at http://fordfuelinjection.com/index.php?p=30

---

Test Video; "...This is a short clip compressed video clip that shows how to test the throttle position sensor on a 5.0L Ford engine with EEC 4 electronics. Test include the TPS signal, reference voltage, signal return and explains how the sensor operates. This is just a scene from a much longer chapter on EEC 4 troubleshooting..."; MIESK5 Note, Suggest Right Clicking this Hot Link & Open in New Window

Source: by Kenneth C at Bad Shoe Productions via youtube.com

miesk5 NOTE; wiring color codes are = to below diagram by SeattleFSB

...

Wiring Diagram in an 89

Source: by SeattleFSB (Seattle FSB) at SuperMotors.net



 

megan

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Aug 6, 2011
Messages
9
Hey, thanks for the reply.

I have listened to every inch of the engine and sprayed almost a whole can of Carb cleaner and not found anything, except for the little yellow tube that has been repaired. Now, as far as pulling codes, my engine light is not on (unless I disconnect the TPS, of course.) Do codes still come up if the check engine light is not on? Also, do you think it is safe to drive with the TPS disconnectedd for a length of time? It seems to solve all of my issues.

Thank you for all of your wonderful advice. Once I make it back to Texas I should stop asking so many questions!

 

miesk5

96 Bronco 5.0
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yo,

Do the Code check even though Check Engine light (CEL) is not on; do both KOEO & KOER as Joe shows in his article.

Because, not all engine faults will set the CEL or a Code.

Call around parts stores other than AZ to see if they will do a Free Code Test on your year.

HATE TO SEE YOU SPEND $, some parts stores and Wal Mart/K MArt sell Code Scanners for your year. I checked WM on-line, but they only show some $40.00 plus readers; so look for something like this version;

Equus 3145 Ford Digital Code Reader

http://www.oreillyauto.com/site/c/detail/EQU1/3145.oap?pt=N0664 $31.99

http://www.sears.com/shc/s/p_10153_12605_00914783000P?prdNo=3&blockNo=3&blockType=G3 $34.99

http://www.amazon.com/Equus-3145-Ford-Digital-Reader/dp/B000EW0KHW/ref=pd_sim_auto_1 $21.99

etc.

Make FORD

Engine Type V8

Liter 5.0

CID 302

Engine Size 5.0L/302

Beginning Year 1981

Ending Year 1995

Live Engine Data Monitoring No

Resets Check Engine Light No

To reset; disconnect batty neg

Continuous Memory Self-Test codes are erased by ungrounding STI before KOEO Self-Test is complete and all KOEO and Continuous Memory codes have been displayed. It is possible to inadvertently erase Continuous Memory codes by ungrounding STI without realizing that KOEO Self-Test is not complete or the processor has not finished displaying all the codes.

there are other brands too.

-------------

The brake vac boost was probably poor due to low/irregular idle (low idle = low engine vacuum to booster & other vac op. items)

the Old & NEW TPS are likely bad;

A NON-Ford NEW TPS failure is sad to say, a common nuisance; I had a new switch fall apart in my hands recently, as well as other crapola parts from CH...

You can try thsoe tests w/ a multimeter I gave you previously.

I have heard of folks driving for a long distance w/Out the TPS connected.

The TPS provides info to the EEC (computer) to adjust fuel flow; so you could have issues with it down the road; lower MPG, maybe spark plug fouling & less power.

when you took the TPS off, idled higher because the TPS wasn't sending proper (idle) voltage back to the EEC. So the EEC compared fuel mixture to intake air & since Ford engineers programmed it this way to use pre-set values , idle increased. In so many words.. At times, I have to close my eyes & think about all the other sensors that provide fuel & air info to the EEC and then what the EEC does; all according to diff situations such as ambient air & engine temps, @ idle, cruise or wide open throttle, etc.

 
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megan

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Aug 6, 2011
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Very informative, thanks.

I was actually going to head out and get a multimeter today. Hopefully I can prove the tps is faulty and get a refund for my $80. I'm kinda in the boonies and Napa is the closest place for 40 miles. But there is a Ford dealer not too far.

My eec tester is different then the one Joe describes. I'm unable to attached a photo but its about the same size, has a black plastic cover, reads EEC TEST in the middle with two little square holes to the left and right. I read you can just stick a paper clip in it but not to sure about that.

Well, of to the parts store...

 

megan

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Aug 6, 2011
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Well I'm an idiot. The connections I was looking for are UNDER the little black plastic piece. Codes to follow...

 

megan

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Wow! That was too easy, once I new what I was looking at. Wish I had done that a long time ago.

Okay, for the KOEO test I got a 63 followed by a 34. TP circuit bellow minimum and EVP voltage above closed limit.

I don't no if I mentioned before but I have cleaned the erg valve.

Now for the engine running test, I got the initial four flashes then I stepped on the brake, turned the wheel and then never got a signal flash or any codes. I'm guessing that is a good thing.

Guess I'm looking at replacing the EVP? And replacing the TPS with a better brand? Any thoughts on how I prove the TPS I got from Napa was faulty so I can get my monies back?

Again, thanks for all the help,

Megan

 

miesk5

96 Bronco 5.0
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yo,

Good that you got the self-test going!! Saved some $$$!!!

63 KOEO - grounded or open circuit; TB base idle mis-set, binding throttle cable

Verify that here is a 5V reference on the Orange/White (O/W)

and 0.1v or less on the Black/White (BK/W) ground wire.

If OK, replace the TPS

I use Ford or Wells, or SMP brands

DTC 34 - bad EVP sensor, clogged exhaust or convertor

DTC 31, 32. 33. 34. 35. 38 or 84; EGR Valve Position (EVP) Sensor & EGR Vacuum Regulator Solenoid (EVR) Testing

Source: by Dustin S (Dustball, Mellow Yellow, Mr. Laser Boy) at http://ylobronc.users.superford.org/documents/egr/

DTC 33 & 34 "...DTC 33 is triggered when the EVP sensor is not closing.... To prevent the EGR valve from opening when the engine is cold, the vacuum line to the EGR valve may be connected to a parted vacuum switch or a computer-controlled solenoid. Vacuum is not allowed to pass to the valve until the engine is warm. EGR isn't needed when the engine is cold, only when it is warm and under load. Any of these codes could indicate a faulty EGR valve as well. as well as a problem in the ...vacuum solenoids' Miesk5 note; TAB & TAD; so repair those vac lines 1st..." Source: by Larry C

These TAD & TAB are next to Coil;

Location pic; "...the Yellow Vacuum Line goes from the TAD Solenoid (driver's side forward solenoid) to the TAD (Diverter) Valve located at the rear of the Intake Manifold. You have to climb up onto the engine to feel the Diverter Valve or remove the Intake Manifold..The Pink Vacuum Line goes from the TAB Solenoid (driver's side rear solenoid) to the passenger side (adjacent to the Vacuum Reservoir Can) and down to the bottom of the TAB (Bypass) Valve..."

Source: by Seattle FS

http://www.supermotors.net/getfile/848247/fullsize/tab-tad-evr-coil2a.jpg

Test; \Key off. Disconnect both solenoid connectors; measure both solenoid resistances. Is each resistance between 50 and 100 ohms?

If not, replace solenoid

 

megan

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Aug 6, 2011
Messages
9
Well the good news is that the code 63 is gone. Bad news is that code 34 remains and so does the brake and idle problem(unless the tps is disconnected).

the tps tested fine, the egr and ev did not so replaced them. Did find another break in the yellow vacuum tube and repaired it. Like I said, problem persists.

Oh, also tested solenoids and were good.

I'm at a loss.

 

miesk5

96 Bronco 5.0
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yo,

I have more on the DTC 34; didn't want to clog it all up until that TPS code was addressed. btw, if you cleared the Codes by disco'ing da battery, code may come back after driven for awhile. But I guess you have driven it for a good distance since the EVP 34 came up again.

DTC 34

in Key On Engine Off (KOEO) or Engine Running (KOER) Self-Test indicates that the EGR valve and/or EGR Valve Position (EVP) sensor may not be fully seated in the closed position. The EVP sensor voltage is greater than the closed limit voltage of 0.67 volt. Because of the preload on the installed EVP sensor, it is very difficult to determine whether the EGR valve is seated or the EVP sensor is in contact with the EGR valve stem..."

428

by rla2005 (Randy)

or..

The EGR valve spring has become weak and it responds too quickly. But, because it is still within the allowed voltage range, w/ no DTC. Keep in mind that the EVP Sensor could also be out of calibration or stuck. So when you disassemble the EVP Sensor from the EGR valve you must determine which was at fault. Also be careful to reassemble them with a new "O" ring. This will ensure that a vacuum leak doesn't occur..." See Diagram

by KEM Parts

Testing & Operation; "...The EGR Valve Position (EVP) sensor monitors the position of the EGR valve pintle. The EVP sensor converts the mechanical movement of the pintle into an electrical voltage signal which is relayed to the PCM. The EVP sensor is a linear potentiometer in which resistance varies with the EGR valve pintle movement.Voltage is fed to the EVP by the signal return circuit. As the EGR is opened the EVP directs more voltage to the EEC and less down the voltage reference circuit. The EVP sensor provides the PCM with information on EGR flow and EGR system failures. The EVP should read between 0.24 and 0.67 volts at idle with a closed EGR valve..." read more

Source: by Ryan M (Fireguy50) at http://fordfuelinjection.com/index.php?p=35

"...Ford EGR systems "...PCM will not operate (OPEN) the EGR valve unless it sees: The engine warmed up to normal operating temperature. TPS at partial throttle. TPS not at Wide Open Throttle (WOT). MAP/MAF must be indicating light or moderate load. A certain amount of computer clock time has to be elapsed..."

Source: by tomco-inc.com

I have to think this through...

---

Check wiring for open high resistance, short to ground between EVP & EEC,

using this Wiring Diagram from Ford Bronco 1989 EVTM:



by SeattleBronco

Engine off, key off; backprobe EEC using long straight pin (I use my better-half's sewing kit pins with large plastic balls on end and clip one meter's lead to it) and inserting it into back of EEC connector

BR/LG to Pin 26

O/W to pin 26 (through a splice hidden in harness) this is the Ref signal

and B/W to Ground

EEC Connector Pin Diagram & Overview



Connector Pin Outs, Bronco & Ford Truck & Van: 4.9, 460, 5.0, 5.8; miesk5 Note, see his Connector Pin Diagram Link above)

Source: by Ryan M (Fireguy50) at http://fordfuelinjection.com/truckpinouts.html

Source: by Fireguy50 (Ryan M) at http://fordfuelinjection.com/?p=3

=====

Next isn't listed by anyone for the 34 Code, but is a good test anyway to rule the EVR out & is a simple multimeter test;

The EGR Vacuum Regulator (EVR) controls the opening and closing of the EGR valve. The EVR is an electromagnetic solenoid and should have between 20-70 ohms resistance between the pins. +12volts should be constant on one side from the EEC Relay, the computer controls the ground signal when EGR flow is needed.

When the EGR Vacuum Regulator (EVR) is off, both ports vent slowly to atsmophere.

To test it mechanically check to see if vacuum is present at the EGR valve with the electrical connector unplugged from the EVR. The top port should not have vacuum! Because that would open the EGR at the wrong times.

With everything connected and the engine running ground out the pin 33 side. The EGR vavle should open and the engine RPM should change. Read More

by Ryan M (Fireguy50) at

http://fordfuelinjection.com/index.php?p=43

================

I forget if you replaced the vac hose to back of engine to combo valve?

-----

Anyone out there that has a vacuum gauge you can use to check vac at idle?

 
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megan

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Aug 6, 2011
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Well, since my last post I decided to take a break and go camping and catch some trout. But before that I ordered a new egr vacuum solenoid valve to be delivered over night(from autozone) to the ranch I was staying at. Well it was not delivered and after calling and bitching to them the part will be shipped to Dallas.

Soooo, after a stressful drive from Colorado to Dallas(I mean stressful not sure my sweet bronco is gonna make it ) I actually made it home.

The next morning with the mail is the erg vacuum solenoid. I replaced the part not expecting anything to happen, but low and behold, the bronco was PERFECT!!!!! The throttle, the brake the idle. EVERYTHING. I took a good trip on the highway (in 108degree temp just to be sure).

Everything performed perfectly. I'm so stoked and grateful for your help and kinda hate autozone.

GRAND CANYON HERE I COME!!!

 
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