closer

Hello all.... long time reader, and first time poster here on the forums.
Here's the deal. I picked up an '85 Iroc from a buddy. It ran before. But had an issue with when you gave it the gas it would die. Anyways he said the Mass airflow sensor was bad. Then he decided to learn how to work on cars and re-do the intake gaskets. And it sat in a barn for 2 years.
Now I finally persuaded hime into selling it to me. I previously helped him put the top-end back together minus installing the dizzy, plug wires, and other odds and ends. I checked timing (it was way off), and the firing order(also way off). So I re-did it all.... Now I can get it to fire and it will kinda idle. But same thing as before...give it alittle gas and it dies. But it has problems starting sometimes. The car has all (almost all) of the vacuum lines capped off(because he lost them all) And he started to take out the smog stuff. My chilton manual has helped alot. But it doesn't show some stuff very well.
Should I A.) just get rid of the TPI and go carb? (mainly because I'm low-budget right now and I have the stuff already)
or B.) try to get the TPI working?

The car is missing little stuff for the emission system. And lord knows if any of the wiring has been hacked up. I know its all out of the loom and alot of the connectors are broken and brittle. Over all the rest of the car is in pretty good shape. Are TPI systems tempermental? I've read some post saying they're a pain, and others stating that it doesn't take much to get one to opperate(note: not opperate well.... just opperate.).

Rolling Thunder

Well for starters i think it would be cheaper to get your TPI set up running well than to convert to carb. I find TPI to be pretty nice and its not really all that bad to keep it running nice. The real problem is when they do have problems without the knowlede about troubleshooting them they give up on fixing them and complain that there tempermental, problematic, or whatever you want to call them. Now on to your situation first without all the emmissions components it will never really run right. Reason being the ECM makes decitions based on the fact that there working or thins there working. For example the AIR injection system pumps fresh air into the exhaust system. Because of this the ECM knows that the 02 sensor will be reading alittle lean and accounts for that fact when calculating the fuel requirements. If there is no AIR system it would expect still expect the o2 sensor to real alittle lean as result of the fresh air it thinks is being pumped in but really isnt and now it will tune the AF ratio to run alittle leaner than is should. So i think for starters i would try to get the emmissions stuff together. My guess though that your underlying stalling problem is your IAC valve has failed.

closer

The only codes I get when I scan it is 33 and 15. I tried swapping out the MAS power and burn off relays. But it didn't change anything. And the code 15 is understandable. The end is broke off the connector. Wouldn't I get a code for the IAC? or would it not throw a code because it can't go past the parameters set for the computer? (being that it's just stuck)
If it runs long enough to rev it up it still runs rough. Would the IAC cause problems throughout the whole RPM range?
Thanks for helping. I'm used to older stuff with a few wires and a carb

Rolling Thunder

Well unfortunately for the IAC motor there is no code. I think they should have implemented one and could have without much difficulty but for some reason they didnt. Now will a IAC effect thought the whole RPM range? Not really. What the IAC valve does is allow a controlled vaccum leak at idle to provide the car with the air it needs to idle. Now once the throttle blades are open the controlled vaccume leak is minimal by comparison and its effects can be tuned out by the computer assumeing it doesnt stall first. However that being said if the idle air control valve fails it could do anything from causeing the car to stall at idle, idle but die out when you rev it, and a whole slew of other problems. One thing you can try is just dissconnecting it. If you dissconnect it and it runs "better" then you have a bad IAC for sure. It wont run well like that but better. Now yo say you also have a code 33 that will cause you problems across the rev range. The way a MAF TPI system works is it directly measures the mass air entering the motor and useing that information and information from other sensors determins how much fuel should be sprayed in. The code 33 as im sure you already know means output of the MAF sensor is saying that there more airflow than than is reasonable for a car running under 2000 rpms and a certant amount of throttle. This obviously confuses the ECM setting the code and because the ECM thinks this sensors output is garbage it uses its own default airflow value instead of the data from the sensor. Obvioulsy it wont run well like this. For troubleshooting this code i found a good page that has pretty much the same diagnostic chart as the GM factory manual. Check it out and see how she does and well go from there. Good luck as i know how it is going from working on a car with a carb and 5-7 wires to fuel injection but once you start to lean about what the sensors do and how the system works a a whole its really not so bad.

http://chevythunder.com/maf_code_33.htm

closer

Okay... I finally got to test the MAF circuit out with the diagram that you linked. Everything points to the MAF being bad. But now I'm also getting the code for my TPS being to high. My chilton manual shows a non-adjustable TPS. But I can clearly tell on my TB that it is adjustable. What voltage or ohms should it be in? And if I disconnect the IAC it won't even hold the idle for the amazing 30seconds it runs. If it's plugged in it'll idle for about 30 secs and then just die like it's running outta gas.
Will a MAF off of a 350TPI work? I think '87 was when they went to speed density right? So will only MAF's from '85-'87 work on my car?

Rolling Thunder

Well if im not mistaken some TPS sensors were adjustable and some were not depending on year listed below is how to adjust the adjustable type. Remember though dont adjust the throttle stop only make adjustments to the TPS sensor. Next i cant really say whats interchangeable as far as MAFs are concerned (might want to check with an autoparts store) i know the v6 MAF will not interchange with the v8s though but Im pretty sure the 5.7 and the 5.0s are the same and i though MAF style TPI systems ran from 85 - 89 switching to MAP style systems in 90-92. Lastly as far as MAFs go if you can possably afford it get a new bosh MAF as remanned ones or rebuilt ones seem to have a terrable tendency to fail in a pretty short order.

https://www.thirdgen.org/tpimod2

flaming-ford

iTrader: (7)

ok well sense your only getting replies from 1 guy heres my take on the situation.

i'm aware the code 33 is maf it will cause various drivability issues throughout your rev range. It is the main sensor metering the fuel ratio your engine needs.

so yes that could be 1 of your problems, but i highly doubt it ends there. my car has a maf going out on it and it still runs. it just runs rough i can still rev it and make it run roughly throughout the rev range and down the road. it just feels like a poorly tuned carburetor, thats all.

my take is this...... check your fuel pressure at the test fitting on your injector rail (little screw in cap on passenger side of the injector rail, near the regulator).

gm electric pumps are notorious for failing. if you are at 38 lbs or higher and you notice no pressure drop then i'll give you my next step.

if you dont have a fuel pressure gauge you can use my old way for checking out these problems.

go buy a $3.50 can of starting fluid..... spray it down your intake tube into the tb... if the idle picks up you either have a big vaccumm leak (s) or b have a bad pump/possibly bad injectors.

personally i like to check for vaccumm leaks with starting fluid or carb cleaner as well. spray the intake base good, around all it's sealing surfaces along with your runners. if idle picks up from spraying at any of those surfaces you probably misinstalled the gasket or intake is warped or well you get the drift.

if your still having trouble check to make sure you don't have your distributor install 180* off and make sure your firing order is correct again..

closer

Part numbers on some site's say the MAF's are interchangable and other's show different part numbers. I'm going to chance it. I bought a used one off of an '88 GTA today. (gotta wait for it to get here now.)
And "flaming-ford"... The car has a new fuel-pump in it. That was what the previous owners thought was wrong with it so they changed it first. Now that's not saying it isn't bad though. I'll have to get a gauge and check it if the sensor doesn't cure it. Also I tried the trick of spraying starting fluid around everything looking for vacuum leaks. But I didn't get anything. It was the first thing I checked because I never trust anyone else's work.
Well... I'm going to go adjust my TPS and go get a fuel gauge and check it out. Since I will have to wait about 3 days before the sensor gets here... I might as well try to eliminate as many possibilities.
Thanks guys... I know what it's like to answer the newbies ?'s. I've been on plenty of forums... But this TPI is new to me and I'm lost. Speaking of TPI... Is there any books that I could read-up on?

afremont

Just to be thorough, Ohm test all your injectors before and after a test run. If you have one that is shorting, that will shut it all down..... just like it's running out of gas.

Rolling Thunder

Well probably the best book ive seen on TPI, although it may not seem like it would be at first, is TPI swappers guide. It really gets into the what things are how they work and differences in the TPI systems over the years. Its just loded with good information. Heres a link to show you what im talkin about.

http://www.amazon.com/Chevy-Injectio.../dp/1884089127

Also in one of the stickies in the TPI forum theres is a pretty decent little artical copied from a magazine about TPI systems and the basics of how it works.