swapped 4.0 in YJ no power and backfires - JeepForum.com
 
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post #1 of 11 Old 09-13-2017, 07:14 AM Thread Starter
4point0YJ
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swapped 4.0 in YJ no power and backfires

Hello,

I have an 89 YJ that i swapped a fuel injected 4.0 with ax15 into. It hesitates to start but will start when i give it some throttle. Then it will idle fine but if you throttle it up or hold the gas around 3000 + RPMS it will back fire out of the exhaust and up through the intake. No power at all when driving..

Here is what i can tell you about the swap.
Block is an 99-01. (all new gaskets)
Intake and heads are from a 96-98.
96 xj ECU
Distributor is from a 96. (is this fine to use with the 01 block?)
Wire harness is a 96.
Changed the idle air contoller
swapped 20gal tank with new fuel pump, lines, filters. Fuel rail has a return line.
New cap, rotor, plugs, and wires.
New coolant sensor
built exhaust with just muffler no cat. has 02 sensor
new coil (good spark)
Fuel pressure seams fine testing tonight.
fire order is good
spliced the wire harness to keep both.
put a 4.2 oil sending unit to use gauge.

I can drive it around the neighborhood but cant get the rpms to high.


I feel that the timing is off. I set it at top dead center and i know you cant move the distributor to set but for some reason feels like timing.

Here are some things i think could be wrong but looking for some help to test/ ideas and get it working.
Map sensor . ?
throttle control sensor?
02 sensor.. never test
ECU from 96 xj believe it was 4wd. (also have 01 tj computer but was only getting spark on 1 and 6 which was prob due to the coil packs? )
distributor ... could be warped

Please let me know any ideas that you might have. Was concerned using a distributor on the 99-01 block.
Could the distributor be no good? heard this happened to another guy..
would the CPS if bad allow the jeep to run?
Could it be any other sensors?

This is a new swap has never ran good before.

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post #2 of 11 Old 09-13-2017, 07:22 AM
Kruzin
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If you installed the distributer just 1 tooth off, it can mess with the timing and act as you describe.

'09 JK Rubicon
'01 XJ Sport
'10 Fusion
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post #3 of 11 Old 09-13-2017, 07:29 AM Thread Starter
4point0YJ
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Well i felt pretty confident since the next tooth in either directing moves the rotor an inch away from the first plug location. Should i try to move it around and see if it gets any better?
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post #4 of 11 Old 09-13-2017, 11:50 AM Thread Starter
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Does anyone know what years xj distributors will work with my 01 block? or does it not matter?
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post #5 of 11 Old 09-13-2017, 07:56 PM
rjbruzan
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They all work but need to be compatable with the ECM. Is the flywheel/flex plate matching the rest of the system?

Of all the things Ive lost
The one I miss most is my mind

Its like a fart in a windstorm
It smells good but thats about it

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post #6 of 11 Old 09-14-2017, 06:40 AM Thread Starter
4point0YJ
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The flywheel is brand new from Napa NCF88193 which would work on anything from 96-01. I did not verify anything older then 96 since that is the oldest that my parts could be. The Crank position sensor is also good for 96-98 and the pig tail works with the harness that i have it connected to. This CPS did come with the wire harness. I did the initial ohms test which it seemed to be fine then tired to unplug the Crank position sensor last night and it would not start at all. Same with the cam position sensor. I am planning on purchasing a new distributor today and confirming the install on it tonight.

The ECU is from a 96 xj. I believe that these components work good together and like i said i can get it to start and idle but any additional throttle you will hear backfires mainly from the exhaust but also from intake.

I confirmed with the guy i purchased it from last night that these things where done (new) to the motor before i dropped it in:

head gasket
lifters
valve seals
ream main bearing
timing chain.

appreciate the help!
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post #7 of 11 Old 09-14-2017, 06:43 AM Thread Starter
4point0YJ
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one additional thing that i could add is that i could not locate the crank position sensor bolts anywhere so i did use grade 8 blots from the hardware store. They were completely threated and did not have the fat bottom to confirm 0 play ion the sensor. I felt that i got it seated correctly but no way to verify without having the bolts. is there a location where i can order these crank position sensor bolts?
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post #8 of 11 Old 09-14-2017, 07:04 AM
rjbruzan
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Dist and correct position is next on the list.
Good luck
Ron

Of all the things Ive lost
The one I miss most is my mind

Its like a fart in a windstorm
It smells good but thats about it

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post #9 of 11 Old 09-14-2017, 12:44 PM Thread Starter
4point0YJ
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just purchased the new one. installing tonight.
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post #10 of 11 Old 09-15-2017, 05:38 AM Thread Starter
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Fixed! I appreciate everyone's help. I am 99% sure that i did not have the cam sensor correctly set when i installed the distributor. I decided to get a new distributor and when i did i reset all the timing. fired right up and runs strong. Attached is the picture that i used to set the cam timing inside the distributor which i never read was something that we needed when setting the timing.
Attached Thumbnails
xj dis.jpg  
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post #11 of 11 Old 09-15-2017, 07:13 AM
Kruzin
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That would do it. Glad you got it sorted out.

'09 JK Rubicon
'01 XJ Sport
'10 Fusion
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