I just picked up another 85 vette, Z51 car, after checking a few things I noticed it has a custom chip, 180 thermostat, and K&N filter.

I also am getting a code 23 and I found out that the TBI cooling is bypassed, heater core to the manifold instead of the TPI.

Any thoughts?

 

What does the code 23 mean.

 

code 23 is the IAT sensor faulty

disconnect the Manifold Air Temperature sensor wiring harness from the MAT sensor and install a jumper between the two wires of the MAT sensor harness. CKT 472 and 452 (usually a tan wire and a black wire). Start the engine and allow it to run until the Check Engine light comes back on. Pull the codes. Is there a Code 23 or 25?

If there is a code 25, then the MAT sensor wiring harness is OK. Check the connection to the MAT sensor; then check the resistance in the MAT sensor. If both are OK, then replace the ECM.

If there is a code 23, the wiring harness has a open circuit. Clear the codes. Connect a jumper wire from the tan wire of the MAT sensor harness to engine block ground. Start the engine and allow it to run until the Check Engine light comes back on. Pull the codes. If code 25 comes up, inspect the black wire (CTK 452) for an open. If either 23 or 25 were generated but neither wire has an open circuit, replace the ECM.

 

Thanks vader86, I will try that...

Anyone seen or know why they bypassed the TPI coolant lines? I have left alone so far...

 

its a 'free' mod that alot of us have

GM routed the coolant thru the TB to keep the plates from freezing in cold weather, only thing is that it must get DAMN cold and you must be going very slow for it to happen. (like alaska-cold)

At any other time it heats up the intake charge, hurting performance, so we bypass it.

Never have i heard of someones plates' freezing.

 

ive been warned (in my f-body days) that bypassing the TB can either throw a code or leave it in open loop.. any thoughts anyone?

 

When I bought my '89, the throttle body coolant line was also by-passed. The reason GM had put it there in the first place was for cold weather running. The hot coolant travelling under the throttle body is supposed to heat the cold incoming air to ensure that all of the fuel is properly atomized and burned during combustion. But, this is only really applicable in EXTREMELY cold temperatures - like winter in Alaska or something (and when was the last time you saw a Corvette driving around in Alaska in the winter time?). Most Corvette owners would never really need to have the coolant line connected to the throttle body, and in fact most disconnect it in an effort to free-up some horsepower when the car is warmed up. It's probably true - especially in the summer time when the incoming air is already fairly warm, and you have REALLY hot coolant running under the throttle body.

I reconnected mine because I prefer to keep my car as stock as possible.


[Modified by TheCorvetteKid, 6:10 PM 4/4/2003]

 

I've had the TB coolant bypassed in my IROC and Vette for years with no problems.

Leave it, as mentioned, it's a "free" mod.

BTW, it you find your MAT/IAT sensor is indeed faulty it would be a good time to relocate the new one into the air filter housing for a truer intake air temp reading. You can get a kit that includes the sensor, wire, groumet and spiral wrap for a very neat installation.



[Modified by 65Z01, 12:15 PM 4/4/2003]

 

I plan on doing this mod in the SUMMER (did I mention is snowed last night) :cry . I do have an example of the throttle body freezing. This occurred on my dad's dodge truck (318) with the throttle body bypass. No not in Alaska, Winnipeg winter.
R/T

 

it wont throw a code, and the open/closed loop is controlled by the O2 sensor mostly, and a cooler intake charge will have no effect on the readings by the oxygen sensor

 

I have it...seems to keep my plenum alot cooler!

 

i drove my car for about 50 miles the other day straight on the expressway and it was about 25 degrees out. have the tb bypass and no problems with it freezing up. i must have to be sub-zero weather out. and that would be the only concern. no code will be tripped. i'm sure we've beaten this topic to death, but i just wanted to report more on the temperature thing.

 

http://www.thirdgen.org/newdesign/te...ntbypass.shtml



HERES WHAT I DID ON MY STEALTHRAM TO CLEAN UP THE ENGINE AND MAKE MORE CLEARANCE FOR THE WATER NECK, (this is the heater manifold under/side of your throttle body for those of you that don,t know) this requires about 5 minutes work with the band saw and belt sander, and any machine shop can do it if you dont have the tools handy in 5 minutes if you show them the pictures, and YES IT REALLY HELPS CLEAN UP THE ENGINE COMPARTMENT AND GAINS LOTS OF WATER NECK CLEARANCE


and yes because it lowers the average incoming air temps the engine sees it allows a denser cooler air that allows slightly more fuel to be efficiently burnt to produce more hp, the amount is small but its there.(5-7 hp) according to what one of my friends saw after the change on his dyno run (NO I DON,T HAVE THE DYNO SHEET HANDY) AND YES ALOT DEPENDS ON THE OUTSIDE AIR TEMP COMPARED TO THE UNDER THE HOOD TEMPS INVOLVED, but I have no reason to doubt his word , and I find no down side after doing the mod to my vette, and yes it does seem to help slightly. and yes it will take your car about 2 more minutes to heat up at idle as far as the plenum temp sensor is concerned , but it runs great with zero problems, and yes your correct if you live where the temps get to below ZERO all the time it may not work for you!

ok first nothings free! youll need to use your skills.time and at least some money, Ill list what Ive found that works, first DO A GOOD TUNE UP!http://www.thirdgen.org/newdesign/tech/tpimod2.shtml

(1)the throttle body bye-pass above,(dont forget the heater manifold MOD ...AFTER YOUVE DRIVEN THE CAR FOR AWHILE to make sure it has NO BAD EFFECTS IN YOUR OPINION!) http://www.ws6.com/mod-8.htm

(2) air foils in the throttle bodybasically a waste of time and money but yes you can get 1-3 hp at 5000rpm http://www.ws6.com/mod-4.htm
(3) cut the top of the air filter cover to allow more airflow (worth up to 10 hp at high rpms) and install a K&N style high flow filter (this also helps but costs some money)

(4) remove screens in the M.A.F. this is good for about 100cfm of flow increase and is a good mod but can cause your engine to idle rough untill the ECU "RE-LEARNS" the differance in improved air flow)

(5) swap to synthetic oilan easy 3-5 hp due to reduced friction

(6) install an (X) pipe in the exhaustresults vary wildly but if you match this to a free flow exhaust and low restriction (CATS)or no-restriction (GUTTED CATS ) a 20-25hp gain is possiable at higher rpms

(7) kick up(ADVANCE your timing about 2 degrees) most cars respond well and it tends to allow the engine to rev, quicker


(8) porting your intake runners,plenum,basean easy 10-15 hp for a weekends work on the stock intake

(9) pocket port your cylinder heads/ reinstall with thinner head gasketa full weekends work and about $100 in gaskets but an easy 20 hp here if you know what your doing!

(10) install a better oil pan, by modifying the stock oil pan with an extendes sump and baffles lots of welding and measureong here but for several hours work and a scrap oil pan or scrap sheet metal,plus a few small hinges the stock pan can have the sunp extended forward and sideways enough that the 5 qt pan can handle 8 qts plus better control the oil (make all patterns from card board first and tape for welds untill you gett all measurements correct then cut the metal and weld the pan, make your mistakes in cardboard first
(11) 1.6 ratio roller rockers worth an easy 10-15 hp