1991 Brougham 305 V8 no power when hot ok when cold

[cadman56]

I am starting a new post on this issue to let all previous respondents know what I have done.  After rechecking all suggestions given.
I asked a couple of hot rodder friends over.  We discovered some carbon in the IAC circuit & cleaned it.  They then set the timing by disconnecting the timing connector wire under the hood.  They never heard of jump wiring in the ALDL connector inside the car.  The timing is now about 1-2 deg. advanced.  The car now starts/runs fine.  I still notice some slight surging during light to medium acceleration.  She cruises fine at all speeds.
I wonder, since the replacement engine is a GM 305 built to 1993 specifications, should I perhaps add a couple more degrees of advance timing?
Thank you,  Larry

[66 Eldo]

Hi Larry,

The Olds 305 is a bit small for your Brougham so a bit more timing will help but don't advance too much. All of my old cars I run about 2 degrees advanced and you can go more but just until there is no pinging. Personally, I would not advance more than 4 degrees.

Have you or your friends checked the total advance and not just the base or initial timing? Distributor breaker plates often get sticky which keeps the mechanical advance from working well or at all. You will need an advance timing light to check this correctly and not by just shining the light at the marks and revving the engine and seeing if the timing mark moves.

Now this mechanical advance talk may be moot if your electronic distributor does not have a moving breaker plate. Not sure what year GM made the switch or if they did at all so maybe someone else knows. The advance still needs to be checked with an advance light to see if the computer is doing it. 

Check out this video from MSD. It does a good job explaining what is going on with timing on distributor ignition systems.

https://www.youtube.com/watch?v=UYGU7mTwsZc

Regarding the surge, sounds like an overactive EGR valve.  Disconnect the vacuum hose to it and see if the surge goes away but remember, EGR cools the combustion and can cause knock and ping when inoperative because of more heat. Advanced timing will also cause knock and ping so you may have ping with both of these mods.

So, a plan would be to set the initial timing 2 to 4 degrees advanced and check for performance and ping. No ping, disconnect the EGR valve and check for no surge and no ping. No ping, you are done but keep an ear on it for a few days and listen closely for ping under heavy acceleration or up hills. If there is ping with the valve disconnected make a delay valve from the metal end of a glass automotive fuse. Drill a 1/16" hole in the metal cap of the fuse and insert that into the vacuum hose to the EGR valve. This will allow less vacuum and cause less EGR action, hopefully allowing the valve to do some work cooling the combustion, reducing emissions and preventing ping,  but not too much causing a surge.

If you have a state emissions inspection, timing and EGR mods will have to be restored to original specs to pass visual testing and it will help reduce tailpipe emissions and help to pass the test. 

[Scot Minesinger]

First thing that came to mind too, EGR valve.  When this has failed me on older higher mileage V-8's it always seemed like the car was fine until it got real warm (running for half hour or so), and then no power/low power at load say up a hill at 45 mph.  After I replaced the EGR, since it was after vacuum lines, full tune up and the like, it sure ran great.  Replace EGR. 

[cadman56]

Thank you for responding.  All parts I have charged are:  EGR valve, MAP sensor, distributor control module, cap, rotor, oxygen sensor.  All parts are AC Delco brand.
I will see about adding a little more timing this coming weekend.  The new crate engine from GM is built to 93 specs.  Perhaps it needs more timing than the 91.
I will repost late this coming weekend.
Larry

[TJ Hopland]

Have you looked at the fuel spray pattern coming out of the injectors?   Lately I have seen a fair number of these where nozzle is partially clogged so you end up with a sort of uneven dribble of fuel instead of the even spray they are supposed to have.  Also at this age the fuel pressure regulator could be failing.   You can buy a refresh kit for these that includes gaskets, orings, and the regulator.   Its about the same cost as a carb rebuild kit  $30-50.

My experience with these engines has been they don't like it when you mess with the base settings.   I bought several trucks over the years that were full of new or used sensors and still didn't run right.   In every case I just went step by step and set things back to factory using the factory procedures and all problems were solved.   Just setting the timing or the base throttle stop didn't help, you had to do both in the correct order.  Part of the throttle procedure was to set or calibrate the idle air control.   I remember learning the hard way that you don't want to have one plugged in with it out of the throttle body, you end up shooting the little plunger thing out like a dart and won't likely find it or the spring again. 

[cadman56]

I didn't think about the injectors or pressure regulator.  Let me look into that too.  Thank you, Larry

[dplotkin]

Have you thought of a clogged catalyst?

Dan

[TJ Hopland]

Have you thought of a clogged catalyst?

Good thought.
   
I have not seen that as often with the EFI cars as you used to see it with carbs but its possible especially if the cat is older than the engine.    Maybe the last engine getting tired or broken damaged it?

[cadman56]

Catalyst & exhaust system is wide open as determined from previous back pressure readings.
I disassembled the EFI yesterday, cleaned, put in new gaskets, seals, & regulator diaphragm.  Just now came back from a 10 mile test drive.  I could not feel any surging & no hesitation from start up.  It did hesitate momentarily only once after getting off of the interstate & pulling out into traffic.
I think it is much better.  Perhaps I should just concentrate on driving it to break in the new engine & transmission. 
I still have the pesky out of balance in the rear at highway speeds.  I have changed tires, rotated tires many times, balanced & re-balanced the tires, & even changed the tires on the rims..  It has to be an out of balance brake drum or bent axle.
Thank you, Larry

[TJ Hopland]

Drums is possible but surprisingly not that common.    I don't see bent axles in cars very often, that usually only happens in the 1/2 ton trucks or hot rods that get abused.  How about drive shaft?  A stiff U joint can make a vibration.

[Jon S]

Years ago they used to balance the tire/wheel and drum by spinning the tire on the car at approximately 60 MPH.  The gadget rubbed against the tire to make it spin and sounded like a vacuum cleaner and told the technician where to add weights both inside and outside.  It did a great job and assured everything was balanced!

[66 Eldo]

Double checking. Did you disable the EGR and test drive it?

The surging if any remaining could be caused by too much flow causing a lean condition. The GM engines of this era and earlier really did not like EGR. I see you replaced the valve but the original one may have been OK, just too much flow.

[cadman56]

There was no difference with the old EGR valve.  Unfortunately I was told the problem was the EGR so I found an identical P/N Delco unit & installed it.  The old one was carboned up but after cleaning it works perfectly, now I have a spare. :-)