I wouldn't think they would charge you for that. It's easy for them to check. Give Fichtner Chev a call tomorrow. They are one of our long-time forum vendors here on Corvetteforum and good folks.

1-800-234-5284 Ask for Bob in parts. He may be able to just plug in your VIN in their computer terminal and it will show any service records in the GM database, so have your complete VIN handy. Might want to wait until the PM or maybe Tuesday since they are often busiest on Monday mornings. Bob is their parts mgr. Good man.

HTH

 

Well, I got everything back together today and still no change with the intermittant no-start issue. Still get P1518 and "reduced engine power", fuel pump not working, etc. I don't know where to look next. I REALLY thought this was going to be it.

 

The 1518 code is the PCM to TAC Module Serial Data Circuit.
DTC P1518

Circuit Description

The throttle actuator control (TAC) module and the powertrain control module (PCM) communicate via a dedicated serial data circuit. This serial data circuit is separate from any other serial data circuit on the vehicle. Accurate transmitting and receiving of serial data requires not only good circuit integrity, but also adequate system voltage. This diagnostic monitors the accuracy of the serial data transmitted between the TAC module and the PCM. If the PCM detects a loss of data or invalid data, this DTC sets.

Conditions for Running the DTC

The ignition switch is in the crank or the run position.
The ignition voltage is greater than 5.23 volts.

Conditions for Setting the DTC

Invalid or missing serial data messages are detected for a predetermined amount of time.
All of the above conditions met for less than 1 second.

Action Taken When the DTC Sets

The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
The control module commands the throttle actuator control (TAC) system to operate in the Reduced Engine Power mode. OR
Under certain conditions the control module commands the engine OFF.
The message center displays Reduced Engine Power.

Conditions for Clearing the MIL/DTC

The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

DTC P1518 sets if the battery voltage is low. If the customer's concern is slow cranking or no crank because battery voltage is low, ignore DTC P1518. Clear any DTCs that may have set from the low battery voltage condition from the memory.

DTC P1518 sets when there is a short to B+ on the TAC module ground circuit. Inspect the fuses for the circuits that are in the TAC module harness, such as the cruise, or the brake. An inspection of the fuses may lead you to the circuit that is shorted to the TAC module ground circuit.

DTC P1518 sets if the TAC module ignition feed circuit is shorted to a B+ supply circuit. The TAC module stays powered-up when the ignition switch is turned off. When the ignition switch is turned on, the TAC module is powered-up before the PCM. DTC P1518 sets because no communication is detected by the TAC module from the PCM. Inspect related circuits for being shorted to a B+ supply circuit.

Inspect the TAC module power and ground circuits and the TAC module/PCM serial data circuits for intermittent connections.

Inspect the TAC module connectors for signs of water intrusion. When water intrusion occurs, multiple DTCs could be set with no DTC circuit or component conditions found during diagnostic testing.

When the TAC module detects a problem within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual problem may correct more than 1 DTC. Keep this in mind when reviewing captured DTC info.

Code 1518 will be stored every time you program and reboot the PCM. This code is a result of the PCM losing communication with the TAC. After your programming is complete turn off and remove the key, wait 10 seconds, put the key back in, and then turn the ignition on (without starting). Enter manual diagnostics on the DIC and clear out all of the codes. You should then be all ready to go.
Your gauges may go blank once after programming. No gauge & HUD readings, check gauges light on, and the DIC locked on its last reading. Pull the battery cable to fix this. From now on, make sure all display data is out of the DIC when programming (hit the gauges button until the DIC is blank) . Make sure all doors are closed, all accessories are off, and the DIC is blank whenever you program

Also, check your battery terminals for corrosion.

 

How many miles on your 98?? Maybe you have a worn out fuel pump. The brushes are what wear out : they get shorter and shorter and the spring behind them exerts less force on them, against the commutator. Sometimes there may not be enough contact pressure for a good enough contact to start the motor turning, but once the pump is runing it is fine. Have a buddy lay down next to the drivers side, within reach of the bottom of the fuel tank. You turn the key to the first position, if you don't hear the pump run, have your buddy smack the bottom of the tank right-away. If the pump then runs...that's your problem : new fuel pump time! I had this exact problem on my 86 C4.

Another thing you can try is connect a small 12 test light at the fuel pump, by the tank (remove the aluminum shield). See if the light illuminates everytime you turn the key to the RUN position. If it lights, and you don't hear the pump, that would confirm my worn pump theory. If it sometimes does not light, then it is the PCM, fuel pump relay, fuse, or wiring.

 

....or just hook up a pressure gauge at the fuel rail......


SebringSixSpeed, if you need help figuring this out give me a call. I'll PM you my number.

 

I am going to go after the fuel system next. I am just going to jumper the under-hood fuel pump relay and see if the pump comes on and runs strong or not. That should isolate the PCM and tell me if the pump is good or not. When the car does run, my gauge at the fuel rail shows a strong 62 psi but of course it shows no pressure when it does not turn on, but I see what you are saying about the pump motor having trouble starting up if it's brushes are getting weak. We'll see tomorrow.

 

Just to document what I tried today...

I used a jumper in place of the fuel pump relay and the fuel pump works perfectly. So the problem exists outside of the fuel system (at least from the relay back to the pump is good). I even changed fuel pump relay again just to make double sure it was not the relay. Also noted is that even with the fuel pump running strong with the jumper in place the engine would still not fire and still got P1518 etc. I guess I'm actually going to have to break down and spend some money on a TAC module, (I have friends with corvettes, but none that would let me take electrical parts off their car to test on mine not that I blame them).

Also tested battery voltage during cranking again as this is the most common cause of our 'ole friend P1518. Charge at rest was 12.8V, and during cranking it dropped to around 11.8V, then when it was running 14.2V. So, all good there still.

(P.S tried calling you today Lucky, no answer, I'll try again)

 

Daily Update:

I didn't have much time to mess with it today but I did make a new observation. If I turn the key to the run position and wait, after exactly 10 seconds the fuel pump will come on (this seems to be repeatable), at which point I can turn the key to start and the engine will fire and run, albiet in "reduced power". Then it's just a matter of clearing the P1518 code and the reduced power goes away and the engine instantly runs normally. (So now I've found a way to always start my car even though it takes about 25 seconds to go through the motions.)

And again for clarity, if I turn the key to the start position prior to the fuel pump coming on the engine will spin but not fire.

Also found out today that the TAC modules are on backorder (GM parts house) with no ETA.

Speaking of the TAC module, I was told there was a TSB and known issue with the 98 TAC modules. Does anyone know what the symptoms were supposed to be other than throwing code P1518?

 

I am an idiot . A happy idiot but an idiot none-the-less.

My car has started perfectly several times a day, everyday, for the last 2 weeks. Which it has not been able to do for the last 6 months so I think its safe to say it's fixed.

Now back to the idiot part. I could have saved myself alot of grief if I had known the real purpose of dielectric tune-up grease. I wrongfully thought it was designed to apply to electrical connections to enhance the conductivity and provide some protection. Turns out that dielectric grease is an electrical insulator and will not conduct electricity. Now guess where I applied it 6 months ago and again about 1 month ago...

...to my freshly cleaned and polished ignition switch contacts.:o

Once that was cleaned away 2 weeks ago (at time of epiphany)...instant reliable starting and no more codes. I have tried everything I know to provoke the issue to return but it has not. Well, finally I think it may be safe to say there is a happy ending to this sad story .

 

Glad you got it fixed.......but geez bro.......