Hello every one. I just installed a 1990 TPI in my 53 chevy. It runs awesome but I have a few minor problems. When I start the car after it sits over night I have to crank it two or three times. When it starts its perfect. I drive it and shut it down when I start it again it starts on the first try but the idle is usually real high. As i drive it maybe 20 mins. it will go back to normal again but than it will stall sometimes when I stop. There is no pollution or egr hooked up and the computer remains in open loop. I think that is because of the new chip. I put new injectors, I.A.C, module, pick up, plugs, wires, cap, and rotor. I scanned it and there are no codes. I did a smoke test for vacum leaks and found it leaking at the trottle body from the T.P.S and the linkage. Will that give it an intermitent problem like that? I do not have the fan hooked up through the computer and did notice when the fan kicks in, the idle will go back to normal. Could the electrical draw be doing something to the I.A.C motor through the computer (am I reaching here?) . By the way it is a 700r4 trans. Well that is my saga. Thanks in advance for any input.... Dave

 

It certainly sounds like the TB is hanging, or the IAC is flaked. What harness did you use for the swap?

 

I used a detail zone harness and a ron francis kit on the rest of the car. I spoke to the guys at the detail zone yesterday and they suggested going back to the stock chip. I didn't realize that they had a vats defeater built into their harness. I drove the car a little bit since and it might be better. It didn't do the crazy idle and stall any more. I will have to do a little more driving with it to make sure. Thanks...... I will keep you posted....Dave

 

Alright, that sounds like a fun project.

The problem I see is that the computer stays in open loop. Are you running headers or anything?

Do you have a scanner? I'm guessing that you do since you know that the car is staying in open loop.

What are the IAC steps at idle?
How fast are the cross counts for the O2 sensor counting?

Even though it isn't the main problem, I would make sure that you fix that vacuum leak since you know where it is at. If the IAC steps are low, then the problem maybe the IAC. If the cross counts are not rising very quickly then the O2 sensor may not be warming up enough to switch the computer into closed loop, this can happen in non-coated headers.

You have a return line to the fuel tank correct? What is the AFPR set at, it sounds almost sounds like the fuel bleed-off is happening way to fast. I will help out as much as I can.

 

I have just recently been having what I think is the same problem with my 89 IROC Vert. Been having all kinds of crazy idle problems, I adjusted my idle to almost 1200rpm to try to even it out. Could you tell me more about how the O2 sensor is affected by uncoated headers? I am running a 305 w/ uncoated headers. Sounds like my problem. Have to drive around worrying about where I can push my car off the road when it stalls in the middle of traffic....always a fun experience. But, I wouldn't trade it for anything Any help would be greatly appreciated, Thanks!


Matt
mjohnston82@hotmail.com

 

Sure no problem. I just had the same problem with my car.

With non-coated headers, the exhaust temperatures are not hot enough for the O2 to be able to read correctly. The computer will try to switch back into open loop mode until the O2 gets hot enough. Usually the O2 sensor will only cool off during idle when the exhaust is minimal, but will then start to heat up when more exhaust is flowing. Another problem is on the headers; the O2 sensor bung is located further away from the head, also keeping it from heating up. Coated headers keep the heat from escaping into the engine bay and will let the O2 sensor reach over 600°, which is the lowest temp it can work with.

Sometimes the sensor will not be cold enough to send the computer back into open loop, but it won't be warm enough to be able to read the O2 counts correctly, which in turn falsifies the voltage being sent to the computer. This would of course make the engine run bad, at least at idle.

A really easy fix is to get a 3-wire O2 sensor. These sensors have a heating element, which will keep the sensor warmed up to working specs. These heated sensors are built to last 100k miles, so don't worry about the heating element be enabled while the engine is running, it will be fine. One wire is returned to the computer, it will be the different colored wire (mine is purple on the new O2 sensor), and the two other wires are the same color. These wires can be switched, but one must be a ground and other needs to be a 12v power with the key on. The fuel pump is often used. Make sure you connect to something that is only on when the key is on, or else you will run the battery down.

Don't use the Bosch as they have a problem with flat lining, get the AC Delco one. Here are a couple pointers.

Part #: AFS-74 (1995 light truck)
Tech Article: http://sethirdgen.org/HO2S.htm

 

The same problem frequently occurs with coated headers as well. Wanna ask me how I know?

It's a good idea to do the conversion to a 3-wire AFS-74 heated O2 sensor whenever installing headers, regardless of if they're coated or not IMO.

 

Hey every one let me start off with a thanks for the input. I have the stock exhaust manifolds on the car with the O2 sensor in stock location. The air tubes for the manifold are removed and plugged. I just put the stock prom back in the car and it seems to be running better but, the idle still seems a little high occasionaly. I ran the car today about 60 or 70 miles and no stalling. Do I have to reset the IAC when I put the new prom in? When I ran a check on the IAC with the scanner it was right on. I forget the #'s but, they where good. I did not pay attention to the O2 crosscounts. I will be able to use the scanner in a few days and I will get the #'s I am reading for the O2 and the IAC. I am hoping the car goes into closed loop with the stock chip back in. Also I am running a stock fuel pressure regulator with an in tank pump and a return line to the tank. I allready hit that problem with the external pump heating up and dropping pressure. The motor is stock I haven't done anything to it yet. I am waiting to get it running right than I will begin to play with it. I also think I am getting better mileage with the stock chip. Thanks again every one. Sorry it took a while to respond I work shifts were I am gone for 24 hours.