1991 Brougham 305 V8 no power when hot ok when cold

[cadman56]

I just installed a new GM 305 crate engine in my 91 Brougham because at 197k miles the old engine was tired even though it ran great.
The new engine runs/drives/accelerates great when cold but when it gets hot is stumbles or gives no acceleration at all.  No codes are showing on the scanner.  New items installed are as follows:  O2 sensor, MAP sensor, EGR (Delco) valve, ignition control module, cap, rotor, & plugs.
Exhaust back pressure never gets over 1/2 psi, only on max throttle in park.  Fuel pressure remains at 12 psi running.
Does anyone have any suggestions?  Thank you in advance.  Larry

[TJ Hopland]

Confirm that the base throttle and timing settings are set correctly to factory specs with the computer put in the proper modes and the correct procedure followed.    I saw a lot of those engines in the trucks that had poor performance and a pile of new parts on em.   About 75% of the time getting those base settings correct solved it. 

IF that does not do it next I would want to get a scan tool on it that can read real time data.  You will want to look at various computer inputs and outputs while its 'cold' then watch what changes when it gets 'warm'.   If its not the above issue its got to be a sensor giving the computer bad information.   Its not missing info or out of range info so you are not getting a check engine light but its just not giving the correct info.   When its cold its likely not reading that sensor, its running off of some default warm up map.  One way to force that to happen would be to unplug the coolant temp sensor for the computer.  That usually forces it to a safe rich warm up mode.   The computer one is usually near the t stat.  The gauge one is the one down between the spark plugs.

Is 12 correct for fuel pressure?   Seems a little low, I was thinking it was like 15.    Did you do a refresh kit on the throttle body when you did the rest of the work?   At this age that would not hurt.   Sometimes you get a little fuel leaking past the injectors due to old O rings.   Also sometimes you get a crud build up around the injectors that slows down the flow.    Fuel pressure regulators eventually fail too. 

One odd thing I heard happen to a guy one time in a Caprice about the same vintage that took him several months to track down and had similar symptoms to yours was a crack in the fuel line in the tank.   It was apparently a small split in the short length of hose between the fuel pump and the rest of the pickup unit inside the tank.   I think he drove it for 6 months that way throwing other parts at it the whole time till he decided to just replace the fuel pump because it was all that was left.   

[Scot Minesinger]

Look at the EGR, this is the classic symptom-no power when well warmed up and difficult to find.

[Dave Shepherd]

Remember in open loop cold, the ecm has not taken over control yet, 12 psi is good, 10-15 is the range, look at temp sensor readings on a scanner when hot, they had a high failure rate, also make sure as mentioned the the base timing is correct, you must disconnect the est wire from the dist to do this, usually brown.

[Scot Minesinger]

If you re-used EGR from original engine, that is almost certainly an issue.

[gary griffin]

Many years ago my cousin had this problem with a souped up Mercury engine. He had solid lifters and when they heated up the stems expanded and kept the valves partially open as it heated up but it ran perfectly when cold. He denied my analysis until he adjusted the valves and it worked. Probably not pertinent here unless the lifters are faulty or someone had replaced them with solid lifters?

The reason I like the earlier cars is because of the styla and the absence of electronic gadgets I do not understand. I was a hot rodder in the 50's and a certified diesel mechanic at 18 and I do not even attempt to work on my modern cars or my diesel truck.  The gadgets make them run better but difficult to maintain because they change them every year it seems

[cadman56]

The EGR valve is a new one.  It is a DELCO one with matching #'s as the original one.
The timing was set to 0 deg. at hot idle by connecting two electrical ports in the ALDL connector inside the car with a jumper wire.
The scanner was connected while driving the car.  Readings were real time & all were in the correct ranges.
Perhaps when the throttle body was off the car I may have damaged something when I sprayed it down with carburetor cleaner.  I did have the TPS off the throttle body while cleaning it but nothing else was removed before cleaning.
Thank you for all the replies given.  Larry

[Glen]

The carb cleaner may be the problem as the oxygen sensor can be damaged by such products.  Check to see if the cleaner is labeled as safe for oxygen sensors. 

[Dan LeBlanc]

If I read correctly, the throttle body was sprayed off the car so as long as the carb cleaner didn't pass through the engine while running, the O2 sensors should be fine.  That said, I was always told that one should never use carburetor cleaner on a throttle body as it can remove the protective coating on it.  Ford cars always had a warning sticker on the throttle body indicating this.

[cadman56]

Hello all.
I guess I will have the car hauled to the repair shop.  The gentleman helping me was a Cadillac service manager for 18 years & now owns his own shop with all the diagnostic tools which we were using at home.  His mechanic has been with him for just about as long.  They keep telling me it is the fuel pump.
My biggest question is:  The old engine ran beautifully, just tired & very high mileage.  What could I have done to mess everything up?
When this gets fixed I will reply to let you all know.  It has to be done soon as I am supposed to drive up to Hickory Corners in mid July to spend a little bit of time with setup & I have several bundles of GM World magazines to get to Paul.
Thank you again, Larry

[76eldo]

Just a thought but make sure the heat riser valve in the exhaust manifold is opening up when it gets hot.

Brian