Hard start and stall/stumble on acceleration

TAYLIN_S

MEMBER
1997 CADILLAC SLS
160,000 MILES

I beleive I have more then one problem that needs addressed.

first off I have replaced the following w oem parts:
all manifold throttle body and intake gaskets
maf
tps
air filter

there is no codes stored and I have absolutely no vaccum leaks. I have checked multiple times. Plugs wires appear to be original. Possible part of the issue. I have not checked the plugs for proper gap or wear

First the vehicle is extremely hard to start when it is cold it will fire then die repeatedly unless u crank for several minutes and pump the gas. I have experieinced this on another vehicle and it was the fpr(fuel pressure regulator).

could this be the issue here?

i have NO codes stored or showing. I scanned w my personal obd pro scanner tool.

Second is once started the vehicle idles normal everything working as it should. When placed in gear it idles rough and on acceleration it cuts out and stalls if u give it more then about 1/8 of the throttle. If u accelerate slowely it drives fine but if u open it up it cuts out and bucks as if its not getting spark or fuel.

i have spoke to another owner that had a similar problem he stated that he replaced his cam positioning sensor and both of his crank positioning sensors. Although he also had no codes. And that fixed the problem for his vehicle

i disconnected the cam positioning sensor and the vehicle will not even attempt to start. So I beleive it to be functioning. Although I have not tested it.

do u think it may be the crank positioning sensors. If so any tips to replaceing them as from, what I can tell they are in a very difficult location to access.

to summarize

issue 1. Hard starting: bad fpr?

issue 2. Stalling under acceleration: bad crank positiong sensor?

1 Reply

FACTORYJACK

MECHANIC
4,159 POSTS

You could have a fuel pressure regulator causing the hard start, or you could have low fuel pressure that is causing both concerns. You can check the fuel pressure regulator by removing the vacuum hose from the regulator and checking for raw fuel. You will want to do this after running, so the rail pressure is up. It would be advised as well to check pressure, as this could be casuing both of your issues. It should boost to 40-45 psi at key on, and be just below that when running. You could have misfiring from secondary ignition faults(plugs/wires). You could also have restricting exhaust, due to clogging in the catalyst.