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I'd Rather Be Blown
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Discussion Starter · #1 ·
I have an 89 Chevy C15. 350/ 700R. It has 200K on it. I bought it with a blown engine (they let it run out of oil. Bad valve cover gasket.) So I knew it needed a new engine when I bought it.
I ordered a crate motor from Summit. Great fit, easy swap.
With the new engine I installed new O2 sensor, Distributor Cap, Rotor and all new plugs and wires. new PCV, ( engine temp control sensor looks new, so I am sure that I replaced it too. can't find the receipt)
I set the timing (per Chilton's) and after I got it tuned up and running great it started with this stumble just off idle, mainly when coming back to idle. Like in a parking lot that kinda stuff. I touch the gas and let off and it stumbles bad. once and a while it will stumble so bad it dies. It is definitely running RITCH when it stumbles.
I have taken it on road trips no problem. Towed a trailer with a Mustang on it 200 miles and back, No problems except just off idle.
OK what I have done to try to fix it..... Vacuum gauge dose not seem to bounce to bad until I open the throttle under load then it bounces some.
#1 It was suggested to check valve lash. the engine had 5oo miles on it so I pulled the valve covers and set them to Chilton's specs.
#2 at idle Tested intake for vacuum leaks with carb cleaner. (3 times) no difference.
#3 Changed Map sensor.
#4 Changed Idle air control valve
#5 changed the injectors even though they looked great.
This truck runs great except right when it comes back down to idle....
I am running out of things to replace.
Help me please
Thank you in advance
Larry
 

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Which Summit engine?

What distributor are you using?

TBI is extremely sensitive to cam timing, the factory cam for the LO5 engine is probably the mildest cam in history. Anything much bigger will cause issues.

Exhaust leaks ahead of the O2 sensor will run the engine rich.

The list of probabilities is pretty long so we need specific details of what engine this is and how you tuned it.

Bogie
 

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Well tps comes to mind right off.

But before you guess by throwing parts at it.

Grab a paperclip or a obd1 tester and plug that thing in turn the key to on(not start) and count the flashes.
That chilton manual or a google search will give you the pins/steps/video/codes.

The computer is very basic. But it will let you know if you have a bad tps or something else. Except a egr sensor that thing never comes up. But that would be a mid to max rpm bogging.

Also inspect and replace your vacume lines. Those plastic lines love to have microcracks.

Check your 02 sensor wiring the wires and connection is located in a spot that is easy to melt.
 

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I'd Rather Be Blown
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91 Posts
Discussion Starter · #6 ·
Which Summit engine?

What distributor are you using?

TBI is extremely sensitive to cam timing, the factory cam for the LO5 engine is probably the mildest cam in history. Anything much bigger will cause issues.

Exhaust leaks ahead of the O2 sensor will run the engine rich.

The list of probabilities is pretty long so we need specific details of what engine this is and how you tuned it.

Bogie
sorry It is a Jegs engine part # 809-12681430 Chevrolet Performance GM goodwrench 350 Cast iron block truck engine. basically I called told them the truck and engine numbers this is what they said I needed and here we are..... the O2 sensor is on the drivers side only and it is located in the cast iron manifold just before the transition to pipe.
Distributer is stock. Not HEI has a coil. Tuning:
Well tps comes to mind right off.

But before you guess by throwing parts at it.

Grab a paperclip or a obd1 tester and plug that thing in turn the key to on(not start) and count the flashes.
That chilton manual or a google search will give you the pins/steps/video/codes.

The computer is very basic. But it will let you know if you have a bad tps or something else. Except a egr sensor that thing never comes up. But that would be a mid to max rpm bogging.

Also inspect and replace your vacuu
Well tps comes to mind right off.

But before you guess by throwing parts at it.

Grab a paperclip or a obd1 tester and plug that thing in turn the key to on(not start) and count the flashes.
That chilton manual or a google search will give you the pins/steps/video/codes.

The computer is very basic. But it will let you know if you have a bad tps or something else. Except a egr sensor that thing never comes up. But that would be a mid to max rpm bogging.

Also inspect and replace your vacume lines. Those plastic lines love to have microcracks.

Check your 02 sensor wiring the wires and connection is located in a spot that is easy to melt.
I happen to have one of the old OBD1 readers..:LOL:... I am getting the 12 code or no codes recorded. :geek: On this one the O2 sensor is in the open on the drivers side manifold. the wires are clean and clear. I have replaced all the vacuum lines that I can and vacuum tested (mouth) the ones that are left. all are good.


Check your 02 sensor wiring the wires and connection is located in a spot that is easy to melt.
TPS is new changed with the MAP sensor.
fired it up set by ear to warm it up. Unplug the tan with Black tracer wire on fire wall set to 0 TDC (per the under hood decal) with light and plug back in.
 
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