88 V20 sub with code 33

After driving on the freeway for a while (15 min+), when I slow down the service engine light comes on and the truck runs rough. When I try to stop, I dont have much for braking power. Sometimes it goes away and runs fine.

I just changed the MAP sensor and it is running rough all the time.

Is there anything else for code 33?

Any other ideas? :banghead:

I also changed the alternator because the gage said about 11 volts, now it says 15.

Thanks

After driving on the freeway for a while (15 min+), when I slow down the service engine light comes on and the truck runs rough. When I try to stop, I dont have much for braking power. Sometimes it goes away and runs fine.

I just changed the MAP sensor and it is running rough all the time.

Is there anything else for code 33?

Any other ideas? :banghead:

I also changed the alternator because the gage said about 11 volts, now it says 15.

Thanks

First thing a code does not say replace part.
In good repair information.
There is repair flow charts for codes.

With a code 33 check for good engine vacuum to map sensor and the wiring from map to computer.
Check you map sensor voltage voltage reading.
What is reading key on engine off and engine idle and and engine under load readings?

You may also have a egr valve sticking open causing map sensor reading to go to pot and rough idle.
With low engine cacumn and lose of breaking power.
Check your engine vacuum and see if it is dropping when it acts up.

Thanks.

I did check the vacuum, but I will check electrical tonight.

Thanks.

I did check the vacuum, but I will check electrical tonight.
Also recheck vacum when it is acting up.
If egr valve is sticking open vacumn goes to pot.

With the key on voltage check, which of the 3 pins on the connector do I check and what should the voltage be?

where is the EGR valve on a TBI 5.7 engine?

With the key on voltage check, which of the 3 pins on the connector do I check and what should the voltage be?

where is the EGR valve on a TBI 5.7 engine?

Map sensor has 3 wire.
One ground and one 5 volt voltage reference and other signal voltage to computer.
Find ground and then find reference 5 volt wire.
After that the other one should be the voltage to computer.
Key on engine off signal voltage to computer should be 4.5 to 5 volts.
Engine running with engine vacume to map and engine at and with idle good.
Map signal to computer should read 1-1.5 volts.
Engine under load voltage should go up to 3-4 volts.

If you can not find egr valve you had better hang up on DIY and get some help from a mechanicl freind or buddie.:grinno:

Egr valves are on right side and little towards rear of intake.
A little 3-4 inch dish shaped thing with vacumn line on top.

Black wire should be ground/ sensor return to pc.
If you have a gray wire it is reference voltage.
If a light green wire it is map voltage to pc.

Post back voltage readings.

As to your first post if you are losing breaking and engine is rough you are losing engine vacuum.

I would say your egr valve is sticking open causing that.

HAHAHA! Just wanted to make sure that I was actually looking at the EGR valve as the manual I have does not illustrate it very well. Might as well ask and be embarrassed than ruin something.

Bingo!!!

The EGR valve was stuck in the open position. Tapped on the end of it to loosen it up and reinstalled and everything runs great now.

Will get a new EGR and replace since the old one was pretty corroded.

Found the water pump leaking a little, so that will get changed this weekend.

Thanks for all the help. This forum is great for keeping my fleet of older cars alive. :)

HAHAHA! Just wanted to make sure that I was actually looking at the EGR valve as the manual I have does not illustrate it very well. Might as well ask and be embarrassed than ruin something.

Bingo!!!

The EGR valve was stuck in the open position. Tapped on the end of it to loosen it up and reinstalled and everything runs great now.

Will get a new EGR and replace since the old one was pretty corroded.

Found the water pump leaking a little, so that will get changed this weekend.

Thanks for all the help. This forum is great for keeping my fleet of older cars alive. :)

You are Welcome and we are glad to help.
10-4 on if do not know always ask.

And thanks for posting back how it went and finding the problem.

Good Luck