Cadillac Repair: 1988 Seville- Backfiring, fuel pressure gauge, camshaft lobes

Question
I brought my Seville to a mechanic who said,I need a tune-up before he could start to find out why it was backfiring.I had this done.Then he said it was the map sensor that was bad.He re-placed the map sensor.Gas was pouring into the carburetor,instead in small amounts. He then told me I need a new on board computer.That this would do it. The car does run better then it did,but the gas thing is bad. What do you think?Is he going in the right direction.Cost so far:$524.00

Answer
Hi Robert,

      Not being there to actually test things it is tough to say what direction he is going in. But if all the parts replaced so far have made an improvement then he is going in the right direction.

      If too much fuel is still getting into the engine the throttle position sensor/TPS and the oxygen sensor/O2 sensor need to be checked and verrified for propper operation and adjustment. Then a fuel pressure gauge needs to be installed to see what the pressure is and if it holds when the key is turned off. Those things all affect the fueling of the engine. Of course if any engine codes are stored they need to be diagnosed and that could fix the problem.

      As far as the backfireing, Cadillac engines of that vintage are known for camshaft lobes going round due to  coolant leaking into the oil through a cracked or loose intake manifold gasket.  If the engine has a rougher idle and backfires when accellerateing or when the throttle is quickly opened then the camshaft needs to be checked to make sure all the valves are opening. Both covers can be removed and the engine ran at idle to make sure all the rocker arms appear to move the same ammount. What also can happen is the bolt that holds the pair of rocker arms can strip out and then the valves can't open. Or the stand for 1 arm can break and that will cause back fireing.

       Those are some other things that need to be checked. Working on the Cadillac engine isn't for everyone and if the wrong shop is working on one they might throw alot of parts at it before the problem is corrected. It might be time to have another shop look at this one to get a second opinion. Otherwise good luck. Bill