HT4100 4.1, 4.5, 4.9 Discussion, 91 Deville 4.9 with no power- Need Help in Cadillac Engine Technical Discussion; My 18 year old son has a 91 Deville with the 4.9L engine. Last week it suddenly began running bad, ...
My 18 year old son has a 91 Deville with the 4.9L engine. Last week it suddenly began running bad, and lost so much power that it seems like it's a 4 cyl. There are no trouble codes set. We've tested the TPS and the ISC, checked and reset the base timing, replaced the plugs, wire, cap and rotor, checked the EGR valve and replaced a marginal (when tested) Oxygen sensor. I don't see any evidence of an intake leak, or evidence of blown head gaskets. The plugs we removed were pretty "sooty", so it appears to be running rich. Anybody have any suggestions on what to look for next?? I have 2 other Cadillacs, one with a 4.1L and one with a 4.5L, over 200K on each and have never had any problems like this.
Thanks in Advance for any suggestions!
Thanks for your quick replies!
The cat. convert is only about 8 mos. old, and it seems to have good flow at the tail pipe. The injectors meter resistance ok, and there is good fuel pressure. This car has always idled a little rough compared to the 87s, but I've had others tell me that's normal for the 4.9. It has always run great, it's quick and it was getting great mileage on highway trips-20 to 24mpg. To me it seems like the timing is waay retarded or there is a massive vacuum leak. How do you test for a leaking intake gasket, I understand that is a problem on 4.9s? Also, how durable is the timing chain? Have these ever jumped a tooth or two? Right now it is idling smoothly but you have to stomp it to get up the driveway.