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Tech501
Tech501, Auto Service Technician
Category: Car
Satisfied Customers: 747
Experience:  38 years exp, ASE Mastertech with L1 Advanced Engine performance
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will turn over but on spark.

Customer Question

just put in a rebiult engine we did the work on it. will turn over but on spark. help, it could be a long,long walk home. auy sugustions?
Submitted: 11 years ago.
Category: Car
Expert:  Tech501 replied 11 years ago.

Might be a good idea to tell us what we're working on here.


Make, model, year and engine size


Is it exactly the same as what came out?

Customer: replied 11 years ago.
Reply to Tech501's Post: 89 jeep charokee.4.0, 6cy, atuomatic. We have fuel, checked spark plugs,fuses, timing, basicly all the ovious.
Customer: replied 11 years ago.
can you help?
Expert:  Tech501 replied 11 years ago.

You need to test 3 basic functions to know where to go from here.



  1. Check for spark at the plug end of the wire (already done)

  2. Check for injecter pulse using a noid light (shown below)

  3. Check fuel pressure using a fuel pressure gauge.

Once we know which of these is dropping out, we'll know which system is having a problem.


Customer: replied 11 years ago.
Reply to Tech501's Post: Coil tests ok, fuel pressure is ok. Should we have 12 VDC at the coil input when cranking?
Expert:  Tech501 replied 11 years ago.

What is the fuel pressure?


Do you have injecter pulse?

Customer: replied 11 years ago.
fuel pressure is almost 40 psi. how do we check the injector pulse ?
Expert:  Tech501 replied 11 years ago.
Just pick up a noid light for about $6 and plug it into the injecter plug and crank the engine. If the bulb flashes, you have power and pulse. The light you need is for "Bosch" type injecters. I know AutoZone carries them, even if the guy at the counter doesn't know what the are.
Customer: replied 11 years ago.
why do you think it has to do with fuel? is there something with it that messes with computer or ignition? not being smart, just we are about 30miles from parts store. and REALLY far from home!
Expert:  Tech501 replied 11 years ago.
The computer fires the injecters using a reference signal that is shared with the ignition system. Knowing if the injecters are firing will tell us whether that signal is arriving or not. No injecter pulse would point to a crank sensor problem. I believe the crank sensor is in the top of the bell housing reading on the flywheel. Make sure the bracket is not bent and the wires are not pinched in the bellhousing and plugged in.
Customer: replied 11 years ago.
did test CPS at plug, got open reading = no continuity. what value should it be?
Customer: replied 11 years ago.
cuold we use a digital multi meter?
Expert:  Tech501 replied 11 years ago.
You can't test a crank sensor that way. You need a lab scope.
Expert:  Steve replied 11 years ago.
I would suggest reinstallig the crank sensor; the gap between teh sensor and the triggering plate on the flywheel is very small when adjusted correctly. When you buy a new sensor, it comes with a little piece of stick on cardboard that attaches to the end of the sensor; you install it so that the cardboard touches the flywneel ring and tighten it down; when the engine is cranked, it tears the piece of cardboard off and it falls away. Try putting about 7 or 8 layers of masking tape pieces on the end of the sensor as a spacer and reinstalling it so it touches the flywheel; that will approximate the gap setting. Also, make sure you havent done something like installing the wrong flywheel, without a triggering ring; or bent the ring during installation...
Customer: replied 11 years ago.
Ok, will try to re-install the trigger (as you suggest with the tape to space) just in case it got bumped, unit is new as of 5-6 months ago. Flywheel is correctly installed with the trigger ring, used the existing. Will turn it by hand to check for anything bent or not quite were it should be!
Expert:  Tech501 replied 11 years ago.
The important thing is the correct air gap (the brackets bend easily) and that the wires aren't caught between the bellhousing and the engine. Pulling the wire when previously pulling thhe engine could have damaged the sensor. I'll tell you though, that by not knowing if we have injecter pulse, we may be chasing the wrong thing.
Customer: replied 11 years ago.
thank You. again, I'm sorry for any trouble I started by having 2 open, I will do better the next time I try to log on,

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