My 96 Grand Cherokee 5.2L takes a long time to start and then runs normal. Replaced fuel filter and replacing fuel pump. During diagnosis with a digital test meter and key on, got 12V at fuse, 12V at fuel relay, swapped relays to element relay. But, no 12V at fuel pump connector. Question, shouldn’t there be 12V at connector to prim the fuel system?
Generally, the fuel pump will engage when the key is first turned on in order to build pressure. It will also turn off afterwards. If there is sufficient pressure, then it may not engage at all.
I think the suggestion to check the fuel pressure at the rail is a good one.
But, are you sure it's fuel pressure or even fuel?
Do the basics. Check the fuel pressure and pull any trouble codes. And if that is all ok, look at your plugs to make sure they are in good shape. Next, check the ignition timing, and compression on the motor.
1. weak spark=worn out plugs and wires/ignition packs
2. NOT ENOUGH OXYGEN=check your air filter
3. not enough compression in cylinders
4. mixture is too lean= check your O2 sensors/fuel regulator/injectors. pull plugs out and check if they have gray buildup on them, sign of lean burn.
5. too much fuel=check your injectors/fuel regulator. basically, crank it till it starts, then shut down right away, and pull several plugs out; if they are wet with gas - well, you got it..
6. overall, are your plugs fouled with anything? oil?
7. you have to have a lot of electricity supplied to ignition components to have nice, strong spark. unfortunately, there are many pieces in the chain of ignition command, that can alter this. starting with poorly charged battery..
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