cdornz28

New fuel pump not too long ago, Was running fine and tripped a few MAF codes, In the meantime while waiting for the new sensor I had unplugged the old one, so I could at least drive the car. A day before I put in the new sensor the car just started to fall on its face at anything over 3,000 RPMS. I assumed something with limp home mode. New MAF and the codes are gone and it still does the same thing. Goes to 3,000 fine, holds there, let off, the tranny shifts, and it does the same thing. In park or neutral it does the same thing if you floor it, but if you are very gradual it will rev up just fine. Must be Fuel or air, but I am lost. Cars an 85 Z28

Chevy86 IROC-Z

iTrader: (17)

Sounds like there may be an issue with the TPS. When you press the pedal, the throttleplates open up right? on the other end of the throttle plates (on the shaft) there is a catch that pushes a flat arm on the TPS. Well when the TPS begin to open, the ECM will see (by resistance) that there is a change in resistance and will make changes within the ECM according to its programmed tables. This will then affest the amount of fuel delivery and spark timing. So I would start by replacing the TPS (throttle position sensor). Then reply with the results. If you get the same response, remove it and get your money back. Here, try this before you go and spend some money.

1. http://webcache.googleusercontent.co...&ct=clnk&gl=us

2. http://mpikas.blogspot.com/2008/08/t...june-2000.html

cdornz28

Sounds good, Ill give that a shot and report back to you. Thanks

vetteoz

iTrader: (13)

What is your Cat like?
When mine blocked up had exactly the same.
Start , run right , wouldn't rev over 3K
Could disconnect cat and run engine to prove one way or other.

Chevy86 IROC-Z

iTrader: (17)

. vetteoz is very experienced. Try out his method too.

cdornz28

Cat has been gutted in this case. I did notice this after i fixed a big exhaust leak though, cars been sitting for a few years. Possible the muffler is clogged?

Chevy86 IROC-Z

iTrader: (17)

Muffler will almost never be clogged because it is a tube or box that has large chambers if you will call it that. The reason why people say that the cat may be clogged is because inside there is platinum honey comb looking filter. If there engine is running very badly, it may cause the platinum to melt, thus causing the tiny openings to collapse, causing restriction. Now lets say that apocalypse has occured within your cat and it falls apart and breaks up, then the pieces will flow with the pressure of the exaust and could possiblily clog up the mufflers chambers. But honostly, Ive never even heard of a muffler being clogged due to a failed cat's internal material structure.

cdornz28

When I gutted the cat, it was fully intact so the chances of that are slim to none then. I've been trying to test my TPS, Probing the blue wire in the center doesnt change the reading on my digital VOM. AM i doing something wrong?

Chevy86 IROC-Z

iTrader: (17)

Probing the back of the connector is possible with paper clips, but you may destroy the small rubber plugs that insulate the metal connectors. If you choose this route, I would suggest you use needles because they are very sharp and not blunt like paper clips and would reduce compromising the protection of the rubber inserts. Here is the mod that I did. I ordered some weatherpack connectors and made a inline testing/voltage reading TPS wiring harness.....

Chevy86 IROC-Z

iTrader: (17)

If you dont wanna go through the trouble of making one, you can always buy it from these sites provided....

1. http://cgi.ebay.com/ebaymotors/85-92...Q5fAccessories

2. http://www.ecklers.com/corvette-thro...ml?dept_id=119

Chevy86 IROC-Z

iTrader: (17)

What settings do you have the voltimeter at? Remember, cars use DC, not AC current.

cdornz28

Voltemeter is on DC, Im trying to understand what wires am i jumping and what ones am I probing. Also today CEL came on for a few seconds. Got the codes and two new ones are 22 TPS Voltage, and 43 EST Problem.

Chevy86 IROC-Z

iTrader: (17)

Code 43= when you disconnected the EST wire to adjust the timing, the ECM sensed a fault with the ignition (mainly the distributor). So dont worry about that. Code 22= you are adjusting the TPS and the ECM sensed a voltage resistance either below or above it's range to operate correctly. Take a look at the picture that I posted. You should probe the very top, and middle wires. When you make good contact with the metal connectors inside the plastic housing, you will get a reading that will be above or below the required voltage range. Now keep in mind, Im not too sure which is positive or negative, but either way, for example, If you get a -.55, just switch the probes (top & middle) around and you'll get .55.

Chevy86 IROC-Z

iTrader: (17)

Now once you get the proper voltage on the TPS, just disconnect the battery for over 30 seconds with the headlights switch pulled out (to drain every bit of power out of the electrical system). Then re-connect and .

cdornz28

Alright. I'll do the tps after work today. Thing about the EST code is i havent touched the timing.

cdornz28

New code today, 24, Fault at speed sensor. Whats this?

Chevy86 IROC-Z

iTrader: (17)

So if you never disconnected the EST wire, then disconnect it, cleen off the metal contacts with starting fluid or Mass Air Flow Sensor spray, then reconnect, then turn on car (if its able to turns on). What year is your thirdgen? As for code 24, does your thirdgen had a speedometer cable attached to the speedometer/tranny? Having the speedometer cable disconnected will set a code 24, unless the VSS is bad. Here is an explaination of code 24-

CODE 24
Trouble Code 24 indicates that the Vehicle Speed Sensor (VSS) is reporting an abnormally low reading when other sensors indicate it should be higher.

The conditions for setting this code are:

• no Code 33 or 34 (MAF Error) is present, and
• the vehicle speed signal indicates < 4 MPH and
• engine speed is between 1400 and 4400 RPM, and
• during a low load condition (LV8 between 50 and 99), and
• transmission not in Park or Neutral, and
• all conditions met for more than 20 seconds

If the code was logged when the vehicle was in motion, the following should be checked:
1) Defective or corroded VSS connections
2) Maladjusted TPS sensor. The TPS should read about 0.42 volts at closed throttle
3) Defective speedometer cable
4) Bad or missing speedo drive gear(s) in tail shaft housing of the transmission
5) Defective VSS
6) Defective ECM

Speed sensor is on the back of the instrument panel. Its yellow in color similar to this one (http://store03.prostores.com/servlet...e-SPEED/Detail).

cdornz28

Excellent explaination, Youve been a huge help. New symptoms, Car in park/neutral and you try to rev it up high(ex. floor it) and it starts top pick up and then falls on its face until it wants to completely die out. I would assume some kind of a fuel problem? Too much air, not enough fuel and its choking out the motor?

cdornz28

Also car is an 85. Where is the EST wire? Im used to a vaccum advance setup.

Chevy86 IROC-Z

iTrader: (17)

On my 86 IROC, the EST is above the AC blower (look at picture below.
Does your dizzy have the coil inside and on top of the dizzy cap? If so, the Ignition Control Module may be going bad, aswell as the Pick-Up Coil (all inside the dizzy cap).

ASE doc

Use an inline spark tester to check for spark when the engine drops out. Your symptoms sound alot like an ignition module/pick up coil failure. Also, someone mentioned catalytic converter. It may be plugged. And while checking the TPS as youre being instructed to do, be sure to sweep test it. I use a lab scope for this but you can also use a dvom by sweeping it slowly and watching for drop outs or glitches.

Chevy86 IROC-Z

iTrader: (17)

de ja vue. When doing the sweep test, I would inspect with a analog multimeter, not digital. The digital is good to get the voltage reading because it is precise and very accurate when trying to achieve a steady voltage reading, but as for the sweep, you can see the needle fluctuate normally or abnormally if there is a faulty voltage spike or drop of voltage/resistance if the TPS's coil is bad. Ask a friend if he gots a analog multimeter, or just go to the parts store, buy the multimeter, use it, then return it to get ur money back. This is an analog voltimeter,,,

ASE doc

Good call, except that since you own a computer controlled vehicle, you really should own a voltmeter. Also, whatever voltmeter you buy needs to be 10Megaohms per volt input impedance to provide accurate readings.

Also, the EST code can be caused by any failure in the EST system. An open circuit, short to ground, or short to power. Also a defective ignition module or ECM can cause code 43. Our 3rd gen technical board has a good diagnostic test sequence for this code which covers any type of failure.

Chevy86 IROC-Z

iTrader: (17)

I agree. Almost anything that has to do with the dizzy/ignition will give you a code 42. A voltimeter/multimeter is a must because all the sensors are voltage/resistance type.

shep236

dude i just solved this issue with my 91 formula firebird. after a bunch of heart ache, i started by unplugging one injector at a time, it turned out to be my number one injector was corrupting my whole rail, i mean my car wouldnt start with the injector plugged in, replaced it runs **** again. but just unplug one injector at time, and only one at a time, see if it gets better, by the way when i found my faulty injector i could rev it rite up, befor it would stumble at 2500-3000.

Chevy86 IROC-Z

iTrader: (17)

Nice bro. If you dont mind me making a fuel injector recommendation. I would definately investigate the Bosch III fuel injectors. There are modified to fit in our fuel rails. There are a couple different kind (19 lb for the 305 and 21 lb for the 350). I got a set of 21 lber's for my 350 for around $160. I will say that Im not dissapointed, but very pleased with the product.

cdornz28

Well i finally got some time to work on the car, Rotor was loose on dizzy so i fixed that and reset the timing. Runs much better on low end, thinking its an ignition coil breaking up.

Chevy86 IROC-Z

iTrader: (17)

Try this at night. It has to be dark outside. Open the hood and turn on the car. Look around to see if there is any arching on the spark plug wires. If you don't see any stray sparks, then turn of the car and visually and phisically inspect the plug wires for any exposed wires. I had this issue once. I could not figure out why I had a dang miss fire until I was checking my tranny fluid at night. So I turned on the IROC, popped the hood, and saw a blue spark. I pulled the plug wire away from the header and the smooth idling came back. Try it tonight.