herreraxto
NAXJA Forum User
- Location
- In the Jeep
The problem is that take too long to star, i already change the spark plugs all the filters, oil and some other things, but that didnt fix the problem what else can i do
ignition problems
- Thread starter herreraxto
- Start date
Matthew Currie
NAXJA Member #760
- Location
- Vermont, land of big clay
Two very common causes of slow start are a bad check valve in the fuel pump and a failing crank position sensor. Suspect the first problem if it takes much longer to crank after sitting overnight than during the day.As an additional test try turning the ignition on and waiting until the fuel pump stops buzzing before cranking. If it starts faster then, it's the check valve. It's your choice whether or not to fix this problem because it really doesn't hurt.
The crank position sensor, on the other hand, is something that really should be replaced if it is going bad, or it will strand you. If your XJ is a pre-91, it should take 4 revolutions of the engine before you get a spark (later ones seem to do it faster), so you'll never get instant firing, but if it takes more, the CPS is a suspect.
The crank position sensor, on the other hand, is something that really should be replaced if it is going bad, or it will strand you. If your XJ is a pre-91, it should take 4 revolutions of the engine before you get a spark (later ones seem to do it faster), so you'll never get instant firing, but if it takes more, the CPS is a suspect.
herreraxto
NAXJA Forum User
- Location
- In the Jeep
where is located the valve of the fuel pump and the crank position sensor
Matthew Currie
NAXJA Member #760
- Location
- Vermont, land of big clay
herreraxto said:
The check valve is inside the fuel pump unit which is inside the fuel tank. This is why one of the options for dealing with it is not to do anything at all except to wait a few seconds before cranking, as I do. Some people have added an external check valve in the lines, but someone else will have to give details on that.
The crankshaft position sensor is located at the rear of the engine at the bell housing. It is hard to spot, but facing toward the rear of the vehicle it is at approximately 1:00 on the driver's side, tucked under the firewall. It is rather hard to reach, and replacing it requires some contortions, a good set of socket-rench extensions, and possibly some new vocabulary words. Not knowing which year XJ you have I can't tell you what the wiring connector looks like, but if you check all the various doohickeys that have wires in that area (aft of the the throttle body), you should find one that leads down toward the bell housing rather than to a sensor or back into the harness, and that will be the one. There are some ohmmeter tests that can be made, but it varies from year to year, so we'll need to know what year you have.
jneary
NAXJA Forum User
- Location
- springfield, virginia
if i remember correctly, way back there was a tsb for that same problem in 1990. it pretty much stated the fuel pump bleeds back after sitting. if it the original, it is probably due. still it should be checked with a fuel pressure gauge. and see if it bleeds back quickly, and on restart see how long it takes to build up pressure. it should come up instantly.
