'87 TBI 350 Troubles

[Jake292]

My '87 with a TBI 350 has been having some troubles recently. it all started a few weeks ago when I pulled into the driveway and the engine stumbled and died. when I started it again, It was backfiring and knocking when I would give it gas to keep it from dieing.

the next moring I checked that I was getting fuel; the pumps cycled, and the injectors were spraying. I then pulled the distributer cap and bumped it over so that #1 cylender was top dead center and the rotor was pointing in the wrong direction. In the evenings of the next week I put in a new timing chain (a good cloyes double roller) and again the rotor was pointing in the wrong directon (I know that the timing chain had slipped because the dots on the gears didnt line up). I then turned the distributer until the rotor was pointed in the right direction. I put the timing light on it and was getting an irregular spark. I replaced the coil and no change so I warantied the Distribiter. After stabbing the new distributer, It fired right up.

the next morning when I started it the engine stumbled adn would only run when I gave it gas and it would back fire. after a few minutes it would idle fine. when I got to school i shut the engine off and tried to start it again to see if it only did it when it was cold and it did the same thing. I drove it like that for a few days til i had time to work on it. I put the timing light on it to check the timeing and it was still on with the spark control wire unplugged. when I pluged it in and looked at the timing it was super advanced(4* from the left side of the mark onthe timing cover) and when I gave it gas it moved speraticly. also when I tried to start it and it stumbled it would idle fine when I unpluged the ESC.

Now it wont even run with the ESC pluged in and it was knocking and back firing with it pluged in so I replaced the knock sensor and saw no change.

I have narrowed it down to something to do with the computer. and I have a feeling that its flooding.

this is a mostly stock engine with only these modifications:

-MSD
-Timing Chain
-New tranny(if it maters)

Im at a loss guys, please help me out!

 

[td87]

did you check to see if your pullling any codes?

 

[Jims86]

Check for codes first, even if no check engine light.
Check the vacuum line to the map sensor, if thats ok and not keaking, pull the 3 wire plug from the map sensor to see if it runs better.
If it seems like its flooding all of a sudden, thats usually the sign of a bad MAP sensor, or a cracked vac line to it.

 

[Jake292]

I didnt get any light when I check for code so maybe im doing it wrong.

didnt see any leaks in the vac lines so i pulled the connector on the map sensor and it idled fine.

 

[td87]

Did you check fuel pressure? Could possibly be a failing fuel pump, I had similar symptoms and fuel pump solved it for me

 

[Jake292]

I checked the Throttle Position sensor and it shows .59v at idle and 4v at wot

 

[Jims86]

Sounds like a bad map sensor, but check the bulb for your check engine light before you go any farther.

 

[Jake292]

ok so I was checking codes wrong. Ive got codes for o2, Map, ESC, and Lean/Rich Exhaust. the MAP and Lean/Rich Exhaust showed up the most though. but the o2 showed first. not sure what shows importance.

 

[Jims86]

for now, go ahead and hook up the Map sensor if you haven't already.
Start the truck , hopefully it will idle enough for the test.
probe the lt green wire from the map sensor plug.
Check the voltage at idle, it shoud read between 1 to 1.5 volts at idle. if any higher, the sensor is bad.
MAP sensor problems cause everything else to read funky

 

[Jake292]

sweeeeet! it was showing almost 4 volts. will replace tomarrow if i have time

 

[Jims86]

sweeeeet! it was showing almost 4 volts. will replace tomarrow if i have time

Yeah, 4 v at idle is close to a wide open throttle reading...making ecm add fuel, makes o2 say "wtf?", makes ECM wonder who dunnit?

Just to confirm, you did the test while the engine was idling?

 

[Jake292]

yeah I had to give it gas at first to get it to idle then it was at idle when i tested it.

 

[Jims86]

yeah I had to give it gas at first to get it to idle then it was at idle when i tested it.

Groovy!

 

[bucket]

I have a question about your timing issue. When you put it at TDC and the rotor was not pointed at #1, was the rotor perhaps pointed directly across from #1? I'm thinking you were just 180* out and needed to rotate the motor one more revolution. It's just odd that the MAP would die at the very same time the timing chain jumped.

 

[Jake292]

it was 180 out when i first stabbed it but im am sure that it is in the right possition because i pulled the #1 plug and felt for the comppression to blow my finger off the hole and the timing mark at the right location.

when the timing chain slipped it was back firing out the throttle body and the exaust so i think that it backfiring would mess the sensor up.

I havnt had time to replace the map sensor yet and probably wont until the new year.