1991 P30 454 intermittent surging, power loss

It could be a vacuum leak. Cracked hose or a bad emission valve. Check the hose going to the EGR solenoid and the solenoid to the EGR valve. Possible bad or stuck EGR valve

I don't think it has been mentioned but, next time it is warmed up and acting up try removing the gas cap and listen for a vacuum sound.
That would point to an emissions problem not venting.
Another wild shot, possible muffler partially blocked.
If it was a Ford you would be spending money on suspension corrections.

I really appreciate everyone’s help, but for right now my time has run out for troubleshooting this. I have to leave with it on a trip tonight for a festival, and I will be gone until after Labor Day. I will have to resume troubleshooting when I get back in September.

When I get back, I will learn how to pull the codes and post them here.

Thank you again for everyone that has contributed, and try to help me.

Gjac wrote:
You say it bogs down when accelerating at low speeds, what does it do at high speeds? It this problem only at low speed? when engine is hot? Does it run better when engine is cool? Does it run fine once you get above a certain speed? Have you checked the timing yet? Base timing should be 4 degrees BTDC, 454's run better when timing is advanced to 9 degrees. It almost sounds like you're not getting advance when you accelerate if your problem is ignition or you're not getting fuel flow from the fuel pump if it is a fuel issue. Your pressure could be fine but if you don't have the correct flow rate, it can cause hesitation. There is a spec for this, x number of units per min. If you pump is original think about how many gals it had to pump at 8 mpg verses your car at 30 mpg over 58k miles.

There seems to be no rhyme or reason, sometimes it will accelerate perfectly fine and it doesn’t matter if the engine is hot or cold. The problem is just at low speed, and accelerating from a full stop. Once it gets up to high speed, it doesn’t seem to have a problem going down the road.

You have changed a lot of parts but it is also necessary to clear the fault codes that may be in your ECM. Unless you clear them there is a good chance that the ECM is still responding to the old faults.

You say it bogs down when accelerating at low speeds, what does it do at high speeds? It this problem only at low speed? when engine is hot? Does it run better when engine is cool? Does it run fine once you get above a certain speed? Have you checked the timing yet? Base timing should be 4 degrees BTDC, 454's run better when timing is advanced to 9 degrees. It almost sounds like you're not getting advance when you accelerate if your problem is ignition or you're not getting fuel flow from the fuel pump if it is a fuel issue. Your pressure could be fine but if you don't have the correct flow rate, it can cause hesitation. There is a spec for this, x number of units per min. If you pump is original think about how many gals it had to pump at 8 mpg verses your car at 30 mpg over 58k miles.

enblethen wrote:
I would not source GM distributor. There are many after-market rebuilt that are better.
If you are going that much work, I would suggest after-market coil and new Lifetime plug wires.
udidwht: 58,000 is not even broken in! Have over 200,000 with no major engine work.

Aftermarket these days equates to China = **** or ****-shoot. If you have 200K in one of these Class A's with a 454 that is good but also an exception rather than the norm.

Definitely pull the codes and at min check fuel pressure and look for vacuum leaks.

You need to check for codes!

**New update**

I rebuilt the TBI throttle body. I really did not find anything wrong with it, but it's done.

Bought a new A1 Cardone distributor. It has the same reluctor design as the original GM. It also has two holes with screens on the base plate, presumably to address the moisture issue inside the distributor. I like this updated design. The new distributor was easy to install with no problem.

Spark plugs were Autolites, I replaced them with AC/Delco.

Spark plug wires were the original AC/Delco. One of them had a large split in it, near cylinder #1. I installed a new set of AC/Delco wires.

**Test drove, no change. Problem is still present.** It bogs down when accelerating at low speeds.**

I tried disconnecting the MAP sensor and guess what, It runs much better!!

Ordered a new AC/Delco MAP sensor, installed it and test drove. Ran good, but only for 15 minutes and the problem is right back.

Disconnected the new MAP sensor, and it runs much better! The hesitation is still there a little bit, but it runs significantly better with the MAP disconnected.

Every time I disconnect the MAP, I plug the vacuum port. FYI

I still haven't looked in to pulling codes on this, but the CEL (Service Engine Soon) light comes on immediatley when the MAP is disconnected and turns off when it is reconnected.

I am starting to wonder if the PCM is bad.

I should have bought a FORD! This thing is very frustrating.

I would not source GM distributor. There are many after-market rebuilt that are better.
If you are going that much work, I would suggest after-market coil and new Lifetime plug wires.
udidwht: 58,000 is not even broken in! Have over 200,000 with no major engine work.