87 5.7 TPI bogs down when hitting 3rd gear
 

Hey community,

So, I puchased this 87 z28 3 months ago, and it ran fine for about a month. After that, the car seemed to bog down whenever it would be going into third gear, or on some turns. The car has been in 3 different shops for the last month and a half. The fuel pressure, sparks and wires, and exhaust system have all been ruled out as the problem. I don't know what else to do, besides take it to a machine shop and have them just turn it into a carb intake. That will cost me around $1600 apparently, i'd rather not do that. I disconnected the MAF sensor and it actually seemed to just run worse off the bat so I dont believe thats the issue. I really just dont know what to do with it. Any suggestion would be appreciated.

Made

You just need to find someone that knows what they are doing and has the right equipment. These cars are not hard to work on.

Of the top of my head, Air temp sensor, MAP sensor, Fuel Pressure regulator, weak EGR valve, or the wiring harness to anyone of those. You need a good s scanner that can read all the sensor values and a person that know what those values should be.

On the spark side you could have a worn distributer, Carbon tracking in the distributer cap, a failing spark module, failing rotor cap. To be sure this is all working right you need an automotive oscilloscope and someone that knows how to use one.

On the engine side you want to make sure you valves are working as the should and you need to make sure you do not have slop in your timing chain. You need a timing light and a vacuum gage and someone that knows how to use them.

A failing injector or any fuel issue would show up on the oscilloscope is they have a portable one.

If everything I mean everything checks out try a ECU. There was a lot of defective ECU replaced under warranty 1986-89 but I also a lot of them replaced because of other issue. You ECU has a GM part number on it and they where mostly used for a couple of years on anything tune port. You just need the prom from inside your ECU.

BTW how is the car at wide open throttle? If it is good at WOT first things I would do is check the MAP sensor input and I would disable the EGR valve and drive it to see if that helps.

Thanks Gorn. I think you are right, I have just been unlucky with who I have taken it too. They all seem to have been really busy, and just did not want to spend the time going over everything. I'll check for a shop with the capabilities you mentioned.

Most shops never want to admit they are lacking in some areas. They tend to hope it the issue will be easy to find. If I had a shop and did not have the above equipment I would not take on an 80s car not running right.

Its a bad time of year, your best bet for finding a good shop is to ask around at car shows or any car event. All you need to say is that you are looking for a shop with GM drivability back ground. Drivability is the term GM uses to describe the engine not running right.

IMO the best shops are the ones started by former GM techs, They are normally smaller shops and may even have a few current GM techs working in the evening. Normally there is a race car or two in the parking lot :)

Turns out it was a throttle position sensor, thanks for the advice and encouragement Gorn :D