Misfires, hesitation and lack of power when hot

[Meridivs]

Here is one of the nicest-running van we ever had with a 3.1L V6 TBI Chevrolet engine that always ran too good to be true.

Few days ago it developed a misfire condition that is very pronounced when the engine is hot/at operating temperature – under load it hesitates like it’s running in 4 cylinders out of 6. When cold it starts right away and runs good & smooth.

Now the van can’t go anywhere – it misfires so severely that the engine stalls and dies at idle.

What we tried so far, to no effect, was:
– changing the spark plugs & wires
– replace the distributor cap & rotor
– replaced the EGR valve
– replaced the IAC valve
– replaced the MAP sensor

Any ideas what we should be looking at next?

We had a lot of 3.1L Chevy TBI engines and none ran so smooth like this one and, all of a sudden, none ran that bad in such a short time…

Topic

[jason]

have u done a compression test if not I would check that next and c if it is a mechanical problem then let us no what the test # are on each cyl

[Rob megee]

It is very likely you have a bad coil or ignition module. There are test to identify which components are bad. When I get time I will post the links. I would look there before moving on to engine mechanical issues.

[John Hugon]

I have some ideas what it could be…but it would be a guess….In my opinion you have to verify your problem before you replace parts. I think this is a very good place to start for diagnosis:
http://ericthecarguy.com/faq/solving-automotive-performance-issues

[Meridivs]

Today we replaced the Ignition Coil – same symptoms.

I had a problem with the Ignition Module on another car – it didn’t start when that happened. I didn’t knew it could also malfunction.

Something interesting happened when we changed the fuel filter – we put some injectors/valve cleaner in the new filter and the engine ran and pulled strong for a while. After that it started to misfire again in 2 hours of running perfectly. Now sometimes it runs ok and sometimes it acts up.

Is there any way to fix this more permanently? We thought of dumping the whole bottle of valve cleaner through the throttle body but a mechanic told us that we can burn the valves this way.

[Rob megee]

I’m not sure we are talking about the same engine. The 3.1l chevy engine I know has three coils on top on the ignition module. One coil is used for two cylinders, so 3 coils for a six cylinder engine. You didn’t say what year? Here is a link for troubleshooting a 3.1. http://easyautodiagnostics.com/index_gm_3.1L_3.4L/index_of_articles_1.php .

[Bill]

Obviously if he changed the distributor cap and rotor it doesn’t have a coil pack.

[Meridivs]

Engine is an ’92 Chevrolet 3.1L V6 TBI

There’s a single coil ignition system which we aready replaced with no effect.

The only thing that really changed something was a shot of valve cleaner in the fuel filter.

Now the problem comes and goes, now it runs good, the next moment it misfires. Pulls better after the valve cleaner but not as before…

[jason]

have u check to see what the fuel psi is and if it drops or gains win it is running. the psi should be 40 to 47 with the ignition on and engine off. it should drop 3 to 10 psi with the motor running. in the past I have noticed that if you have a small blockage the needle will bounce a lot. If not go back to mechanical I always rule out the mechanical first if the problem is not just in your face and on the early cars it is much harder than plugin in a computer. while u can plug them up it just don’t tell as much.

[Rob megee]

[quote=”wysetech” post=99675]Obviously if he changed the distributor cap and rotor it doesn’t have a coil pack.[/quote]

Sorry, I missed that. I saw 3.1 and assumed it was a dis. My error, thanks for pointing that out.

[Aj santos]

Check connection to ur ecu loose connection can cause misfire

[EricTheCarGuy]

The performance issue article covers many of the steps in diagnosing a problem like this. I would suggest you read through it before replacing anymore parts.

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

One thing in particular you might check for is vacuum leaks. It’s quite common for intake gaskets to go bad and cause performance issues. There is a video on how to do this in the article I posted for you.

Good luck and keep us posted.

[Author]

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