Need help with a problem before I replace everything (and still dont fix it)
Thread Starter
Drifting
Joined: May 2001
Posts: 1,295
Likes: 2
From: Surprise Arizona
Need help with a problem before I replace everything (and still dont fix it)
My 88 with the 4+3 has a problem I need help trying to figure out.
The engine has this hesitation when the throttle is opened. The engine will just bog a bit (and sometimes backfire through the intake when cold) before the RPM start to rise. Its kind of anoying.
The 4+3 overdrive is supposed to kick down just like an automatic trans. Mine will stay engaged until you push the button on the shifter, then it will disengage. If you take off hard from a stop the overdrive should hold out till fourth gear. Mine comes in as soon as you get in to second. Even if you are at full throttle.
It has a Hypertech chip, 180 stat instead of the 160. New TPS set at .54 closed, 4.2 WOT.
The other night I had it on the interstate. After running up to about 120 and doing some full throttle runs in between, the hesitation problem dissapeared, The overdrive started to work correctly also. I got an SES light at the same time everything started to work. Codes were 21 and 42. Code 21 is TPS signal high, thats why I replaced the TPS. Code 42 is EST circuit open or ECM. Checked the conections to the module on the side of the A/C blower, I think that is the EST module. all seem okay.
The next day when I took the car out both problems were back. Cleared the codes. No codes since?
What to do next?
The engine has this hesitation when the throttle is opened. The engine will just bog a bit (and sometimes backfire through the intake when cold) before the RPM start to rise. Its kind of anoying.
The 4+3 overdrive is supposed to kick down just like an automatic trans. Mine will stay engaged until you push the button on the shifter, then it will disengage. If you take off hard from a stop the overdrive should hold out till fourth gear. Mine comes in as soon as you get in to second. Even if you are at full throttle.
It has a Hypertech chip, 180 stat instead of the 160. New TPS set at .54 closed, 4.2 WOT.
The other night I had it on the interstate. After running up to about 120 and doing some full throttle runs in between, the hesitation problem dissapeared, The overdrive started to work correctly also. I got an SES light at the same time everything started to work. Codes were 21 and 42. Code 21 is TPS signal high, thats why I replaced the TPS. Code 42 is EST circuit open or ECM. Checked the conections to the module on the side of the A/C blower, I think that is the EST module. all seem okay.
The next day when I took the car out both problems were back. Cleared the codes. No codes since?
What to do next?
Burning Brakes
Joined: Nov 2000
Posts: 855
Likes: 0
Re: Need help with a problem before I replace everything (Paul G)
The tan/blk EST wire (the one you disconnect to time the car) carries 5 volts to the ignition module, which tells the distributor to take its commands from the ECM, when there is no volts (i.e disconnected) this tells the distributor to ingore commands from the ecm and use base timing. If you have a problem with an EST short then your car might only be getting base timing intermintently and causing the back fire?
Burning Brakes
Joined: Feb 2000
Posts: 958
Likes: 1
From: SF Bay area, CA USA
Re: Need help with a problem before I replace everything (Paul G)
I would start the adjusting your TPS. A code 21 means the TPS voltage is too high at idle.
Check out this site for expalnation of setting the TPS. You will need a voltmeter to do it. http://members.tripod.com/theviperpi.../throtbod.html
Check out this site for expalnation of setting the TPS. You will need a voltmeter to do it. http://members.tripod.com/theviperpi.../throtbod.html
Thread Starter
Drifting
Joined: May 2001
Posts: 1,295
Likes: 2
From: Surprise Arizona
Re: Need help with a problem before I replace everything (weekendwrench)
Please explain this TPS. My original TPS would only put out 4.1 volts when the arm was moved full stroke, hanging loose, NOT screwed to the throttle body. I replaced it with a brand new AC Delco TPS. With the new one hanging loose it will only put out 4.2 volts when the arm is moved full stroke. I am getting this voltage from the 2 top wires. Between the top and bottom wire I get 4.99 volts. I am using a Fluke DVM. I have the TPS adjusted to .54 volts closed throttle, to 4.2 volts WOT. 4.2 is all it will put out anyway. Is this new TPS unit bad?
Burning Brakes
Joined: Nov 2000
Posts: 855
Likes: 0
Re: Need help with a problem before I replace everything (Paul G)
I'm not sure what the parameters, are (don't have my manuals with me) but any voltage over 4 volts is showing the computer the throttle is at WOT, so I don't think your problem lies there.
Burning Brakes
Joined: Feb 2000
Posts: 958
Likes: 1
From: SF Bay area, CA USA
Re: Need help with a problem before I replace everything (Paul G)
It sounds like you are measuring it correctly. It is the voltage at closed throttle you need to be concerned about for the code you are getting. I would think if you are getting over 4 volts at wide open you are probably o.k.. Remember you can change the alignment of both screws and effect the voltage readings.
Are you still getting a code 21?
Are you still getting a code 21?
Thread Starter
Drifting
Joined: May 2001
Posts: 1,295
Likes: 2
From: Surprise Arizona
Re: Need help with a problem before I replace everything (weekendwrench)
I have not gotten any more codes. Both problems are still there. It just seems strange that the problems go away after some hard driving. I never really noticed the overdrive problem when I first got the car. I thought it was normal for it to do what it does. I was really getting on the car this spring when the overdrive started to kick down automatically. Did some checking and found out that is is supposed to kick down under hard throttle. Both problems seem to be related because they both go away at the same time, and return at the same time.
Burning Brakes
Joined: Feb 2000
Posts: 958
Likes: 1
From: SF Bay area, CA USA
Re: Need help with a problem before I replace everything (Paul G)
On my 87 there is a overdrive relay on the firewall just to the passenger side of center. It is near the fuel pump relay. It doesn't take much acceleration to get my OD to kick off.
Have you checked to see if your timing is set correctly? Any leaks in the duct from the MAF to the throttle body? You might also check for vacuum leaks around the intake manifold, runners and plenum. I use starting fluid and spray around the intake with the car idling and listen for a pick up in rpm. Others use propane. It is flamable so be careful and keep a fire extiguisher near by.
Have you checked to see if your timing is set correctly? Any leaks in the duct from the MAF to the throttle body? You might also check for vacuum leaks around the intake manifold, runners and plenum. I use starting fluid and spray around the intake with the car idling and listen for a pick up in rpm. Others use propane. It is flamable so be careful and keep a fire extiguisher near by.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski