89base

My 89 2.5 TBI motor is tired yet still gets me down the road. Tired meaning; leak-down test no.1 cyl hear a lot of air through oil filler cap. a 50% leakage ( 40/80). Other cylinders closer to 15% leakage. I have a chance to buy a motor from a 94 Wrangler under $600, 118k miles on it. With COVID 19, I have a lot of time to make the swap. I have heard the porting on the "newer" motors with multipoint injection are different than the old TBI inlet porting. In that case I would need to reuse my TBI head. Question: is the porting different enough that I would have to reuse the TBI head on the 94 block ? Also understand the flywheel will need to be changed due to the ignition timing coming from the sequencing of slots.

As a follow up: The timing chain and sprockets along with the tensioner were replaced. The tensioner being the worst for wear. It was at the end of travel. It operates be advancing to a tension position then locking in that position by engaging small grooves in it's plastic body. On mine these engaging grooves were worn smooth not allowing it to lock into position but sliding back and forth. The chain had appreceable wear also. Now the engine performs as I'd expect a 4 cyl. In case anyone is interested in the symptoms : Engine would start and idle normal. But going down the road in 5th, it would take a lot of gas pedal to go 55 mph. The gas mileage was poor also ( 10-12 mpg). No timing chain noise up front. My final clue was the degree of crankshaft movement I had while checking distributor indexing ( see my initial question ).

89 MJ with 2.5l engine 5 spd. 208K miles Told it was not the original engiine ( don't know this for sure). I'm checking the distributor alignment ( indexing ). Engine starts and idles smooth Indexing looks to be where it should be but: During the crankshaft rotation to TDC, I found this. Take the crankshaft to TDC then backed it up and noticed that the rotor did not move right away so I checked position of the timing marks this time. In this back and forth movement of the crankshaft I found a crankshaft rotation of 10 to 12 degrees before the rotor would follow movement. Does that sound to be within limits or is it a sign of a worn timing chain that needs to be changed ? If this is a worn timing chain, what driveabilitly issues would I notice ? Thanks.

Thanks for all the info. Here in Michigan it's to cold to spend much time in the garage so this change-out may wait for warmer weather. The MJ is not a daily driver so no hurry. Did find a 2.5 with 155K miles, removed from a Wrangler $400 only 75 miles away

The 2.5L in my 89 MJ is getting tired. (45/80 leakdown no1 cyl. being worse ). What model and what years can I look for in the Jeep line up to replace this motor ? Understanding I will need to change the TBI intake manifold If I find a MPI engine. What other things would I need to switch over from the TBI engine ? General price range for an engine ? Thanks.

As a follow up on this post: Ordered the correct O2 sensor Bosch 12008. Also ordered a rebuilt ECU as there was no measured O2 sensor ref voltage on ECU connector pin 35. The ECU is a Cardone 79-4763. Installed and now O2 sensor output varies as measured by an analog volt meter. Further fine tuning under the hood: checked the TPS Ref and Sig voltage: Ref.= 4.96 vdc X .17 should equal .84 vdc actual reading .38 w/ key on engine off. Adjusted TPS as near as possible to the .84 VDC. Question: what ( if any) will be the noticeable effect of this .46vdc change ( MJ is a manual transmission ) Note: This MJ has run well without any problems, just fine tuning to spec's.

Answered my question last evening about the ECU compatibility. Yes, the 86 ECU works in place of the 89 ECU. Engine runs as it did with the 89 ECU. About the O2 sensor; I read an explanation in the MJ tech section about the Renix systems supplying voltage to the O2 sensor. Meaning the Renix system uses the Titania type variable resistance sensor, here is an excerpt from that article: "The third wire, also black is a voltage feed wire, 5 volts, from the ECU to the O2 sensor. The O2 sensor is an O2 concentration sensitive variable resistor. At optimal O2 concentration the 5 volt input feed to the O2 sensor drops to 2.45 volts due to losses across the O2 sensor to ground. That same wire if disconnected from the O2 sensor will read 5 volts constant to ground. At idle that voltage should read 1-4 volts oscillating quickly back and forth roughly once every second. At 2000 rpm it should run between 2 and 3 volts max, and is optimally running between 2.3 and 2.6 volts at 2000 rpm (in park). A digital meter can NOT be used for reading the O2 sensor voltage, but it can be used to test the ground and the 12-14 volts to the heater and the 5 volt feed from the ECU with power on and engine off. You must use an old style analog meter with the needle gauge on the display to see the voltage swing back and forth with the engine runing. " With that understanding,using a Zirconia type Oxygen sensor would prohibit the ECU functioning as it should as it produces a voltage with engine running ( zero to 1 VDC ). Bottom line: should I see voltage on the O2 sensor plug (coming from the ECU w/ Sensor not connected) as the above article said ? Thanks. 89base

I have an 89 MJ with the 2.5 engine. Really bad gas mileage. Checked the O2 sensor plug for ECU voltage w/o the sensor connected. Zip, zero from the ECU. Suspect I blew something in the ECM when I wired a 4 wire O2 sensor in place of the 3 wire unit using the ground point from the ECU as a heater ground. Point is, no VDC on the O2 sensor plug. Yes I'll trace continuity back from the plug to the ECU plug , next step. If that checks okay, then the ECU must be toast. ( the truck runs well on this ECU other than the O2 / bad mileage problem ). Said all that to say this: I have a spare ECU from an 86 MJ 2.5 engine. Will this be compatible with my 89 ECU ? Side note: this Comanche Club is fantastic for information, it has helped me so much during my restoration Thanks, John 89base