Extreme backfiring, loss of power and hesitation.

THEWOLF

MEMBER
1989 CADILLAC DEVILLE
4.5L
V8
FWD
AUTOMATIC
125,000 MILES

Hello,
My 1989 DeVille is experiencing extreme backfiring, hesitation, and loss of power/power surging. When driving the car it lags, then starts to hesitate/surge, and then backfires. I've blown both the Cat., And the muffler. So far we've done a complete tune up, replaced the coil, and distributor, replaced the fuel pump, and the ECM(computer). The car seemed to mellow for about 50 miles after the computer was changed, but then reverted to it's old ways. Not sure what else is really left except maybe the timing chain, or maybe the crank or cam shaft. Also according to a different mechanic then the one currently changing all of the parts, spark, and pressure are good. So any help woukd be greatly appreciated. Thanks.

3 Replies

HMAC300

MECHANIC
48,601 POSTS

Scan for codes and check firing order but it may be a head gasket or worn camshaft

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Monday, November 10th, 2014 AT 4:10 PM

THEWOLF

MEMBER
2 POSTS

Gonna assume a head gasket gone bad would result in compression loss somewhere in one of the cylinders, but compression is fine. Crank shaft is possible, and if that is what it is, is there a reliable test, or am I stuck with yanking the thing out for a look see? Something I forgot to mention is that it is worse under power. It will rough idle in park, but not as frequently, or as hard as when it is in drive. We also changed the smog pump. Something else of note. When the car is turned off after a little while there is a loud thump that sounds like something falling in the trunk, and feels like someone hit me in the rear neither being the case. I thought it was caused by the exhaust pipe cooling down, and the metal flexing. Not sure though.