Intermittent rough run, any clues?

[WarnFleXJ]

The easiest to get at and try is the one to the power brake booster. HOWEVER, it will give you the ability to let in a lot of air, or just a little, and it's disconnecting has nothing to do with the engine other than causing a vacuum leak - no sensors on teh other end. Just put your thumb over the port right away and ease it away to try different amounts of 'loss'. See how it responds with a little open and how it does as you open more.

You might aught to check your injector pulse. I own an 2000 Xj with an 4.0L with at one time i had the same problem, I checked the pulse rate it was there because the injector driver is in the ECM so the signal is there from the ECM but not getting through the injector when all said and done it was the #3 injector replaced that on injector she ran like a champ. Good Luck hope this helped. Also with the above comment you can also use injector cleaner spray to find the vacuum leak. Spray all vacuum lines and hoses with the spray if RPMS' rise where you spray then suspect that hose/line.

 

[dutchjeep]

You might aught to check your injector pulse. I own an 2000 Xj with an 4.0L with at one time i had the same problem, I checked the pulse rate it was there because the injector driver is in the ECM so the signal is there from the ECM but not getting through the injector when all said and done it was the #3 injector replaced that on injector she ran like a champ. Good Luck hope this helped. Also with the above comment you can also use injector cleaner spray to find the vacuum leak. Spray all vacuum lines and hoses with the spray if RPMS' rise where you spray then suspect that hose/line.

How does one check the pulse rate on the injectors? Can I do that with a multimeter or do I need some more esotheric set of toys for that? Is something that makes a lot of sense to me to check but I just don't know how to systemetically check those injectors. How'd you do that?

Thanks, --Tim

 

[dutchjeep]

Ok, have had a quick look at the vacuum lines etc. Few questions (see picture below).

1) What is the black deposit around the area indicated by the red arrow on the intake manifold? It's very local only around that connector.

2) What does the tube indicated by the green arrow do? The cap is on kind'a loose, but maybe that's fine.

3) The brake booster vaccum line, is that the one indicated by the blue arrow? So that would be the one to disconnect if I want to check what vaccum variations do when it's running rough, right?

Thanks for input, sorry for my ignorance!