Hi guys,
Im the guy that has the 84, last week we determined needed a computer.

http://forums.corvetteforum.com/show...24&forum_id=48


Well I took it for that ride.
I got about 10 miles from home & went thru a drive thru restruant, Well it got hot in line the fan came on, & the check engine light came on.
I drove away from there about 1/4 mile & turned right onto the entrance ramp of the highway, & she bucked & loss power, kinda sputtered.
Then it was alright.
If I wasnt already on the ramp I would of turn towards home.
So the next exit is 4 miles by then I figured it was ok,no more problems.

Drove 50 miles,stoped & started at the store then on to the inlaws.
No problem.
On the way home it went 50 miles no problem, was in a gas station talking for a minuet & it was getting hot but I wasnt there long enough for it to get hot.
Almost home & she bucked somemore.
Even in a straight line I could feel it wasnt there,no power, like no gas but not dead.
It seems like on turns its worse.
Full tank of gas.
When I'd turn I could expect some bucking.
I made it home, turned right into the driveway & started to go up a hill & it died.
We laughed, kinda of sigh of relieve,& it making it all the way then dieing in the drive way. Good car.
It started right back up ,I continued up the hill, I held my foot steady on the gas but it would buck,spinning tires & stalling 4 times before I got up the hill.
My code checker was at home so it was my first chance to see what code it was throwing.
34 MAP.
I drove it to work were I park it,& checked again, 34 MAP.
I think the fuel pump is giveing me a warning sign. Its never been changed.
The MAP sensor is 4 years old, good conection.
What do you guys think?
Thaks again for your continued support.

 

I like a failing MAP for this... and a bad FP, too. I think that the xfire crew uses the TPI FP as a mod, but I don't remember for sure.

you have a PM.

 

Its wierd the car ran good with a bad computer. Change computer & it starts bucking.
I didnt get your Pm.

 

Ok I got the PM.

 

 

Thanks

 

From what I've been reading on your posts its sounds like you may have and electrical short or maybe even a faulty ecm connector.
I would also recommend having a FSM for your car. Its been the best investment I ever made.
When reviewing your other thread, I believe I read that your connector to the ecm was corroded. If so you may want to clean that up.
I would first check voltage to the map sensor your looking for 4-6 volts between pins A and C
If below 4 volts you may have a short in ckt 416. or a faulty ecm connector, pin 11
If you have between 4-6 volts you may even check ecm connector pin 20. or and open short in ckt 432.
The interesting part about both scenarios is they both lead back to the ecm connector.
Good luck

 

Thanks qws, I cleaned the ecc connectors very good.
They are clean.
Pins A&C ?
I know theres 3 wires on the MAP but I forget there color.
Are you saying check voltage at the sensor or at the ECC?
Thanks.
PS remember none of this happened before the new computer.
Also why does turning the car upset it?

 

unplug the wire harness that goes to the map sensor. If you look at it real close it should be inprinted on the connector I believe: A, B, C. The two outer terminals should be the A and C. The good news with this is at least your showing a Code and that should help point you into the right direction. If your ECM connector has been cleaned before and maybe even a few times your problem could still be in that connector. But first things first. According to the manual you first want to check the voltage and see what that reading is. A code 34 map sensor (low input voltage) is the extended name for the code that you have got

 

I used to think the same thing but have learned that there is no differance whether you use the 84 FP or any of the TPI FP's. The CFI wants to see 9-13 psi. A higher psi pressure from the FP will benefit you at higher RPMs or topend but with the CFI restriction at the intake it renders this upgrade useless. However if you port the intake and allow more room for it to breathe I can see how a higher psi FP can help

 

Thanks again.
So I just back probe the outer two connectors & check for 4-6 volts.
Is this with the car running?
What does it mean if its within 4-6.?

 

Ignition on, and engine stopped
Remove the jumper between b and c
check your voltage between a and c
if 4-6 volts
1) disconnect ecm connector, check for an open or a short to ground in ckt 432, if the ckt 432 is ok, pin 20 on the ecm connector could be faulty.

MAP sensor responds to changes in the manifold pressure or vacuum. Have you tested your vaccum with a gauge to see what that pressure is?
If it were the MAP sensor and it failed , the ecm would substitude a fixed value and use the TPS to control fuel delivery. Code 34 will set when signal is too low when the ignition is turned on.

My gut feeling is that this has something to do with that ecm connector. I know you have cleaned the terminals but have you read out the terminals to make sure that you have a good connection with the wire?

 

One more thing
Terminal A- is +5V at pin 11
Terminal B- is pin 20 (ckt 432)
Terminal C-is map return to pin 14
Read out your terminals to the pin connector to be sure you have no breaks

 

Sounds like your getting excellent advice. The only thing I would point to and qws already hit on it-you just worked in the ECM area, go back and double check the connection. The good news is you're now getting a code you can work with.

 

Yes, but... Besides that, back before the ECM was replaced, a scanner had a vacuum reading (via MAP output) that didn't agree with a vacuum gauge. Based on history, I'd say that the MAP deserves close scrutiny.



Pretty much the right conclusion, but for the wrong reasons. The fuel pump doesn't "make" pressure. The resistance to flow cause by the regulator, is what causes and regulates the fuel pressure. As with a TPI, the CFI fuel pump is capable of pressure higher than what it is regulated at. IF a pump is needed, the additional capacity of the TPI pump, to provide a higher pressure on a regular basis, MAY translate into a longer pump life, due to it not being worked as close to it's designed capacity. The fuel pressure will not change, and that will not result in a performance increase over a GOOD stock pump, that is already meeting the demand.

7thvet,
My suggestions, and beyond the mostly good advice above, are first, get your own FSM. It is great when someone is willing to regurgitate one to you, word for word, but it really isn't the same.

TEST your fuel pump. It could be the problem, including the cornering. Don't forget the fuel filter and the sock.

Lastly, take a close look at your MAP. For starters, your FSM will give you a range of readings for YOUR altitude, with the engine off.

RACE ON!!!

 

Thanks for clearing that up for me
I didn't want to give out an opinion, only facts. Just so happen I had mine out while online. I know what is like not to have a FSM manual. The best investment I ever made. Just so happens I've ended up with 2, my second 84 came with one too

I didn't notice in the other thread but has the fuel filter been changed?

 

I'd like to point out a few things if memory serves correct. 1. he had reported replacing 4-or 5 02s, because he believed there was a rich condition-no codes, isn't that right?,2. he had conflicting info-ECM saying one thing, scanner saying another, vacumn? 3. he found a corroded terminal on the ECM connector. 4. he said , after replacing the ECM, for a short period everything was great-except he couldn't pass emissions! 5. Now he has a MAP code-which indicates the ECM is
now reporting (communicating) a problem. It may be just coincidence that the MAP now has a problem, or maybe it had one for sometime-nevertheless-it's a trouble shooting tree now. The FSM has a step by step tree to trouble shoot it and it should be easily resolved! BTW, when you stated it "seemed worse on corners" I'd bet my ole lady it was fuel pump or a low on gas problem-I'm still not sure it isn't.

 

Well guys, looose wire at the MAP.
Loose nut behind the wheel is more like it.
I should have looked before I posted.
The connector clip is broke off. I know I bought a replacement connector, but I think I didnt want to cut wires to install it.
So it was taped together, & the other day I untaped it to see if disconnecting the MAP made it run different.Then didnt retape it.
So probably when I cornered or gased it the wire moved just enough or the motor torqued enough to get the low voltage condition.
So now I need to test drive it again.
Sorry to rack brains needlessly.
Thanks for the help.

 

Lot of loose nuts around here-including me you most likely found your problem. Let us know.

 

thats a nice cheap fix, glad to hear you got in going. Now take it out and smoke em up!