Tach Jumps

[Tom G.]

My Tach just started to jump on my 88 Bronco. Never happens at idle just starts to jump from about 1300 to 3400 RPM's driving down the road. Haven't tinker with anything except to replace the A/C compressor. Any ideas or help

 

[Bronc76]

Any change in engine performance while driving?

 

[miesk5]

yo Again Tom;

Try a Self Test by BroncoJoe19

run it around to heat the engine up and shift thru all gears incl Reverse.

then; turn off all accesories/lights, etc.

Do KOEO portion first

For Key On Engine Running (KOER) portion, the engine has to be @ normal operating temp.

Post any codes found here or look em up in my broncolinks.com site.

A guess;

Throttle Position Sensor (TPS)

Overview, Ford part numbers & pics; "...Monitors the throttle opening for the computer to adjust fuel flow. FAILURE SYMPTOMS, Hesitation, tip in surge, engine pinging,no torque converter lock-up. "Check Engine" light on. Inspect for proper operation and adjust voltages when necessary. Check for corrosion on connectors..."

Source: by tomco-inc http://www.tomco-inc.com/Catalog/tps%20sensors.pdf

Test, Location, Operation, etc.

Source: by Xris

"...DIAGNOSIS: Decided it must be TPS...yeah I know...look for codes. This time I did not have too! See below if you even suspect you have a TPS issue. There is a voltage test you can perform to determine if the TPS is within normal oerating ranges.

First you will need to locate the TPS and plug. The TPS is located on the end of the throttle shaft on the throttle body (TB). By monitoring the output voltge from the TPS, the PCM can determine fuel delivery based on the throttle valve angle. A broken or loose TPS can casue intermittent bursts of fuel from the injector and/or an unstable idle. Any problems with the TPS will throw codes 23, 53 or 63 for the two digit system or 122 through 125 for the three digit code system.

TO CHECK THE TPS: Turn the ignition to ON (engine not running) and install the probes of the volt-meter into the ground wire (black) and the signal wire (green) on the backside of the electrical connector. This process is called BACKPROBING. Turn your key to the on position (the engine need not be running to perform this test). Your meter should read 0.50-1.0 volts at idle. FYI...because the black probe kept on sliping out of the back of the plug I grounded it to the battery, which works just fine also.

http://www.supermotors.org/getfile/266541/fullsize/2%20TPS%20Plug%20II.JPG

Rotate the throttle to the full-open position and the sensor should increase voltage to 4.0-5.0 volts. The maximum voltage I got was 1.85 volts. So I was for sure this must be the problem. Many have said that if you do not get a steady increase in voltage, this also is a sign of a bad TPS.

THROTTLE BODY REMOVAL: In most case you will need to remove the TB to get to the TPS. First remove intake hoses and the throttle cable assembly.

http://www.supermotors.org/getfile/266543/fullsize/4%20TB%20INtake%20Hose%20Off.JPG

The bolts that hold the throttle assembly (located on top of the intake) are 1/2"

http://www.supermotors.org/getfile/266544/fullsize/5%20Throttle%20Assembly.JPG

Next disconnect IAC plug, coolant hoses and vacuum lines. Remove the four bolts holding the TB to the intake. These bolts are 3/8".

http://www.supermotors.org/getfile/266545/fullsize/6%20Remove%20IAC%20Plug.JPG

This is the bottom of the TB where the TPS is located

http://www.supermotors.org/getfile/266548/fullsize/9%20TB%20Removed%20Old%20TPS.JPG

the TB gasket. take it off before you clean the TB.

While you have this apart...check the intake and TB for crud build-up

CLEAN TB AND INTAKE: he used Super Tech CARB Cleaner from Wally Mart

Here is the new sensor to be installed...normal pracie was $54.99 my cost was $34.50, comes with a life-time warranty. While I was at it I decided to pick up a NEW Haynes manual. By the time it was all said and done I got the sensor and manual for original price of the sensor...

INSTALL: Prior to removing the TPS, remove the negative battery cable. Some truck years will require that you scribe a mark across the sensor and the TB to ensure that the new sensor is installed in the same exact location. I was not sure about my truck so I did it anyway.

Remove the two phillips head screws and remove the sensor.

Reinstall the TB in reverse order. Make sure you hook vac lines, coolant lines and sensor wires up.

FordFuelInjection.com has a great article on TPS. Please link to Fireguy's site for more information. Hopefully I have not left anything out. I'm sure you will let me know if I did! Good luck!

Xris has more pics at his SM site on this; http://www.supermotors.org/clubs/superford/vehicles/registry/detail.php?id=5183&s=29981#content

--

and; Throttle Position Sensor (TPS) Screws TSB 89-14-07 for 89 & prior Light Truck & Car Lines

Source: by Ford via Steve83 (Steve, That dirty old truck) at http://www.supermotors.net/registry/media/747753

TSB 89-14-07 TPS Screws

Publication Date: JULY 14, 1989

FORD: 1983-89 CROWN VICTORIA, MUSTANG, TEMPO, THUNDERBIRD

1984-89 ******

1986-89 TAURUS

LINCOLN-MERCURY: 1983-89 CONTINENTAL, COUGAR, GRAND MARQUIS, MARK VII, TOPAZ, TOWN CAR

1984-87 LYNX

MERKUR: 1985-89 ALL MERKUR LINES

LIGHT TRUCK: 1983-89 ALL LIGHT TRUCK LINES

ISSUE: All Throttle Position Sensor (TPS) mounting screws have a "Pozidrive" head. The "Pozidrive" head looks a lot like a Phillips ***** head. Use of a Phillips head screwdriver to remove a "Pozidrive" ***** will normally result in a rounded or damaged ***** head. Many technicians think it is an overtorqued or "frozen" *****. An adhesive was also used as a thread sealant starting with the 1988 model year. This adhesive requires still more effort to loosen and remove the *****.

ACTION: To prevent rounded or damaged ***** heads when servicing the TPS mounting screws, technicians should always use a #2 "Pozidrive" screwdriver.



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 4troubleshooting..."

Source: by Kenneth C at Bad Shoe Productions via youtube.com http://www.youtube.com/badshoeproductions#p/u/0/lJEGigONelc

 

[Tom G.]

Any change in engine performance while driving?

No change in performance. I can hear there is no change in actual RPM. Thanks for the replies

 

[BroncoJoe19]

I think that the tach gets its signal from the wire that comes from the tach side of the coil. I'd look at that connection first.

 

[Tom G.]

I think that the tach gets its signal from the wire that comes from the tach side of the coil. I'd look at that connection first.

I'll check before I start doing the tests

 

[BRONCOGRL911]

My tach on my 89 does the same thing around the same RPM,It started doing it about a year ago.My bronco used to stall all the time until it was fully warmed up.It would pop and stumble on acceleration so I suspected the TPS sensor and I replaced it in February and all seemed well,I could start it without being in it to keep it going and it accelerated fine but I still noticed the tach would occasionally jump on the highway and now it's starting to do the stalling and stumbling again.Maybe my TPS sensor has gone bad again? I know that I should try to stick to motorcraft but the cost and availability make it difficult.I sell automotive parts for a small company and we usually get the top names in aftermarket parts.

 

[Krafty]

as far as the tack is concerned its a short circuit, or surge from another circuit.

 

[Eddiefishback]

I have had this happen quite a few times on different cars/trucks. My problem everytime was Sparkplug wires wearing out...Changed them and it stopped