1995 Cadillac STS 1995 Cadillac STS Seville Won't Start, Ba

ZAHMIN89

MEMBER
1995 CADILLAC STS
V8
FWD
AUTOMATIC
124,000 MILES

So far I have replaced the starter which was in pieces and the battery which was dead. I got it to run, but it would backfire sometimes when I started it up and it was idling very rough. I replaced the intake manifold gasket and the o-ring for the intake manifold as well, thinking that an air leak could explain how rough it was running. Since I replaced them, the car will not start. Instead it backfires under the engine or in the engine, I can't tell. I'm thinking it's either a timing problem or an engine valve problem that's causing fuel to get into the intake manifold during startup and causing the backfiring. Am I correct? What do I need to do to get it to start?

8 Replies

RASMATAZ

MECHANIC
75,992 POSTS

If you're sure there's no false air/vacuum leakage do below changing I/M gasket will not throw off the valve/ ignition timing unless you didn't set the distributor back in correctly-

Do a fuel pressure check with a fuel pressure tester designed for your fuel system to rule out the fuel filter/pressure regulator and fuel pump then come back and give me the pressure readings so I can evaluate the situation and what direction you need to go-this is where we start the diagnosis.

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Monday, May 12th, 2008 AT 4:10 AM

BUZZSAW

MECHANIC
1,198 POSTS

You need to scan your codes, off and warmer on the heater controls, with the key in the on position

its distributorless so timming isnt affected

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Monday, May 12th, 2008 AT 9:29 AM

ZAHMIN89

MEMBER
5 POSTS

Initially we thought we had a leak in the I/M gasket that was letting fuel under the I/M but we have since figured out that there is a flapper door on the end of the I/M. The flames we have seen are coming out of that. While the car is cranking and trying to start we can hear the little flapper opening and closing. After cranking for a few seconds we get a loud pop that sometimes shoots flame out the intake. I am thinking this can be a timing issue but not certain. I have never seen ignition into the intake before so this is new territory for me. I will read the codes tonight and see what it says. I will have to go get a fuel pressure gauge to check that. Thanks for your help with this I will let you know what I find tonight.

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Monday, May 12th, 2008 AT 10:24 AM

ZAHMIN89

MEMBER
5 POSTS

I read the codes and looked them up last night and everything came up as either a KAM reset or a suspension code. The battery was dead for a long time on this car and I assume that is why everything is reset.

Is it likely this ignition into the I/M can be caused by a vacuum leak? I was looking at the vacuum lines last night and saw a cracked rubber boot that has three lines into the throttle body (working from memory here). I also have one open port coming out of a cannister on the throttle body. I cannot find any disconnected hose however. I will try to find a vacuum schematic and follow it to see what I am missing. Thanks.

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Tuesday, May 13th, 2008 AT 9:35 AM

BUZZSAW