1993 Allante Engine has loud pop when starting - intake manifold cover plenum
 

Our 1993 Allante Engine, with approx 85,000 miles, is driven about once every three weeks or so (its a garage queen).

This afternoon, as we attempted to start the car to take it out, a loud explosion or pop came from the engine (it didn't start) and when we opened the hood, smoke was pouring off the engine and one of the covers had popped off the engine. It took about ten minutes for the smoke to stop and we have not, and we're not going to try starting it again.

We have a mechanic who is going to look at the car, but we wanted some idea of what happened, and what we may be in for.

Any suggestions or ideas?

David

It is possible for this to happen if key is turned to start engine turns over doesn't start and key is turned back run then back to start quickly. Other possibility is fuel leak within intake manifold - this only applies to 93-94 with box style intake. Early intakes do not have backfire valves to relieve pressure caused by backfire and intake break. Even with backfire valve intake can still break. If manifold top is loose something is likely to be broke, do not try to start engine if visible cracking is present.

aside from what slowroll said, the early '93 Allante had a recall for the plenum. if yours was not corrected, it is a very likely issue. the recall involved the installation of grommets. if yours doesnt have the spacers/grommets. do not try to start the engine, as well as what slowroll said: cracking. fuel leak, etc ...

text from the thread listed below:

there are rubber grommets under the cover retaining bolts that will give if there is an explosion inside the plenum. Without the give of the rubber grommets, in the event of an internal explosion (such as from a leaky fuel pressure regulator) the plenum blows up and has to be replaced. I have no idea if the plenums will accept both covers or not. The only plenum I replaced personally was a later style, and it had been hit and cracked by a piston that went up through the valley. I sold an early plenum to someone who had the explosion in a very early '93 Allante'. But he would have used the cover that came with the one I sold him. You could always pick up a plenum off a '94 Concours, Seville, or Eldorado Northstar. Those are all the grommet style.

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https://www.cadillacforum.com/forum/...ead.php?t=4834

Northstar Plenum fire and explosion, most probable causes: leaky fuel regulator, original engine cover.

Conclussion; this ailment is only associated with the 1st generation NorthStars


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