Is this the V6 manifold vacuum port?

Is the 225 intake manifold vacuum connection the square 'pipe plug' shown in center of pic? Its sort of on the passenger side rear of the manifold. I have never done a vacuum test so I just want to make sure I am going in the right direction before getting too far into it or if there is a better way. Also, assuming that is the correct vacuum port, it seems as though I would need some sort of adapter to connect the gauge hose to the port.



For the bigger picture and for anyone to confirm or advise if my trouble shooting procedure is on the right track... I am getting rich fuel mixture based on exhaust smell and black exhaust residue, exhaust backfire (can this indicate too rich?), no need to choke even when cold, fuel mileage, and of course plug fouling. I checked and cleaned all plugs today - getting black fouling on all of them, but significantly more on the right bank. The left side seemed like it had a light 'fresher' coat of fouling on top more traditional grey color. I put the leftside breather cap back in for better airflow - wondering if that was responsible for the fresh fouling. But, the right side wasn't fresh - much worse and may be related to the infrequent frequent exhaust backfire (during rapid engine deceleration - such as shifting or letting off the gas quickly) that occurs on the right side as well as a not so encouraging 'clacking' noise coming from the right bank. Did identify the fuel mix screws are both 1.5 turns out (Rochester 2G).

I am going to check (and set if needed) initial timing, then do the vacuum test - both to tune the carb mixing screws and also to see if there might be anything else going on with one of the cylinders (not good). Will also look into regulating the fuel pressure or at least testing to see if its too high from the aftermarket electric fuel pump.

One last question - can you test an active plug wire's continuity by putting an induction timing light clamp on it (obviously not to check timing but just to see if it triggers the light)?

thanks all
and to Warloch (and Ward) for the help today.

James

 

The quicky check on the plug wire is all I am looking for at the moment - was just a little concerned I might have damaged a plug wire and I understand the check doesn't guarantee the plug is firing correctly.

As for the vacuum port - There is also a vacuum 'nipple' right behind the carb on the left side that the heater vacuum line connects to. Can I use that for the vacuum test as opposed the pipe-plug shown in the pic. Might save some hassle removing the plug and finding an adapter for the gauge to fit into it.

thanks,

James

 

Seems like using the heater control vac port will be easiest.

Walt - when you mention the vacuum the tube at the base of the carb, do you mean the one that would connect to the distributor for vacuum advance or a different one?

Haven't had a chance to investigate any further so far today (Sunday) or test vacuum, but the more I think the problem through the more I want to follow up on the fuel pump pressure. Warloch suggested many of the same ideas about idle mixture screws not having any effect at higher revs as well as fuel pressure being too high. A PO installed an electric fuel pump and I have no idea what fuel pressure it runs - but I can check it with my new vacuum and fuel pressure gauge! I will check the FSM for proper fuel pressure number. Also, I want to ensure electric fuel pump is installed correctly - IIRC its on the line from the tank to the old fuel pump and then goes through the old pump and there is a return line in there somewhere. Does this sound right? I assume I would want to old pump to be inoperable? - any way to verify this? Haven't looked at it yet so maybe its obvious?

As for an exhaust heat riser - I have to look more into this, don't know much about it. Is it possible that its been removed by the PO when headers were installed?

Some of the other stuff you mention has not been a problem - I drive it almost daily so it gets lots of fresh fuel weekly and just changed oil this past week and no concerns. As I continue to investigate I can check compression for each cylinder, especially if the vacuum reading indicates something off. Will check vacuum and fuel pressure first and see what that indicates, and then might have to investigate carb jet size or float levels.

FYI about the distributor - I believe its the Delco (non HEI) distributor. Can post a pic to help verify.

thanks all

 

Procedure question for fuel pump pressure test (sorry I've never done a lot of this and what little I have done I did 15 years ago for an 84CJ7).

It looks like I can test fuel pump pressure just from connecting the fuel line from the pump directly into the pressure gauge and close off the return line, but I am concerned about how much fuel will spill and certainly don't want to cause a fire (extinguisher ready to go!). Will it work to run the fuel line into a T-fitting and with two outlines: one to the pressure gauge and one into an container to collect the fuel? Return line pinched plugged in either case.

thanks - James

 

Thanks Ken - method work fine. Just didn't want an unexpected fuel spill. Doesn't look like high fuel pressure is the problem as its still running the stock style mechanical pump and all my fuel readings seemed okay (3.5-4 psi with some minor fluctuation). If I am correct (rarely the case) the electric fuel pump is just a 2.5 psi 'primer' pump to help fill the carb when starting - would this make sense? I know the primer pump does not need to run after starting, but haven't been able to determine if it shuts off or not. Its wired into the ignition and comes on at acc spot before cranking - but not sure if it ever gets cut off when cranking and therafter. Could this cause a problem if it stays on other than potentially burning out the primer pump a lot faster? I have a return line from the mechanical pump for what it matters.

I didn't take a pic - but the distributor is Delco assuming metal 'window' and cap screws as opposed to clips are only Delco and not Prestolite. No idea what was originally in there, but shouldn't really matter....except for possible change in initial timing. All Delco distributors should be 5 BTDC for initial timing correct? Some prestolite's required 0 BTC? Timing is off - much closer to 0 than 5 BTDC so maybe the distributor was changed to Delco and the timing was set to stock Prestolite? Anyway will set that tomorrow and go from there.

If the timing is really off by this much, then its been that way for a while and it just keeps running...but at what cost in internal damage?
Learning the hard way as I go.

thanks all for you help
James

 

Thanks - I get what you are saying. Just wondering if someone might have set the initial timing to 0 thinking it was a prestolite distributor. My FSM suggests all Delco distributors set to 5 BTDC and some prestolite applications/model, but at least one prestolite application/model was to be 0 BTDC. Not that I know for sure or why - just what is shown in the FSM (if I even remember correctly - was a late night and I don't have the manual in front of me).

Just to rule out any chance of the wrong distributor, the odd fire cap should have even/equal spaced plug connections (which is what I have) as opposed to an even fire cap which has un-equal spacing of the plugs.

Another timing question: Although I am setting initial timing at idle with carb port vacuum hose disconnected from distributor and plugged, I should not expect to see any significant change in timing at idle after reconnecting the vacuum as the throttle is not open and its a carb port as opposed to constant manifold vacuum - correct? Just asking to get better understanding of how the vacuum advance works.

After getting initial timing set, I do want to bypass the electric pump and see if if the mechanical is fully functional. The fuel pressure tests indicate more pressure at the carb than just coming out of the electric pump but before the mechanical pump. I am happy to run it without the primer pump if it starts and runs fine without it - might have to actually use the manual choke for once.

many thanks - James

 

Yep - that is what I got using the heater control vacuum port. Kind of a fast vibration/fluctuation between 14 and 15. Get good kickdown followed by increased vacuum (just over 20) when throttle is opened. Looks good for the most part to this untrained eye.

Did this after setting initial timing for 5 BTDC - distributor is Delco as best as I can tell looking at cap and rotor and vacuum advance without removing the whole distributor (which is probably a goo idea from Ken). ALso the immediate improvement on idle from 0 to 5 BTDC seemed obvious even to my ear. Then tested vacuum as well as used vacuum and my ear to adjust idle mix screws on carb. Had to readjust idle screw lower a couple times and then retweak each mixture screw but it all seems really good compared to where it was. Got the idle down to just under 700 - not quite FSM recommended 650 but my tach gauge may not be all that accurate. Probably is not perfect but its a good start for me and many thanks to all of you.

Question: is there a way to see if the vacuum advance on the distributor is operating? I tested the carb port for vacuum and get essentially zero at idle and good vacuum when throttle is opened - I think this is correct from what I understand? As for the vacuum advance on the distributor, I haven't even looked at the FSM so my apologies if its a repeated trivial question.