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Showing results for tags '2.5l troubleshooting'.
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I'm at my wits end troubleshooting my lil 2.5L engine. I googled and found your page from about a year ago. 1990 jeep wrangle 25l engine timing. Today I thought about timing. It misses, like running on only 2 cylinders when at low speed and and only pulling slightly. As I move into mid and upper rpm range it stops missing. I still do not have much acceleration but at least it stops missing. I've check and/or changed every sensor it has. TPS is only rough since I have not gotten my laser tach to work yet. In checking fuel I have only 10 psi so I know that's a problem. This started about a month after the SMOG guy changed the O2 sensor to pass smog. I've check the voltage when hot and it's within spec. I also had massive exhaust gasket leak so I cleaned the surfaces and replace the gasket. I'm a machine mechanic from way back in the Navy so I'm not just a new mechanic. I just can't quite figure this one out. I'll check timing tomorrow. Lowell -
Hi Guys! I've scoured these pages the last couple days, but can't find anything that matches my specific dilemma. I have a 1990 Wrangler w/ 150k miles on it, recent acquisition by my future son-in-law. It was running relatively fine, but it quit suddenly on a recent trip. It started cutting out when hitting bumps, then finally quit altogether. After dragging it home, hitting the forums, swapping a few parts, following all the sensor tests and wrapping my head around this TBI setup, I am afraid I have a partially dead ECU. -All ignition parts replaced- Ignition Module, Coil, Wires, Cap and Rotor, Plugs. -The truck will crank the engine just fine, but has NO spark at coil or plugs, and NO gas at the injector. The fuel pump comes on with ignition switch for 1-2 sec, there is fuel in the line at the throttle body, I have not checked fuel pressure yet. -A new CPS was installed, I checked the CPS, 217 Ohms (slightly low), 0.54 VAC while cranking the engine. - All other sensors checked out nominal. There is 5 VDC to the TPS and MAP sensors, so the ECU is not entirely fried. -While tracing the sensor wiring, I found a wire broken internally between the CPS sensor and the ECU (red-white wire tied to pin 28), I'm guessing that was the root cause of the failure. I'm afraid the ECU board may have been damaged in the process of the wire failing while driving. -I am looking for information about what I should be seeing for the output signals for the Ignition Module and Fuel Injector from the ECU. I expect they will be low voltage AC pulses, grounding the DC power supplied to the Ignition Module and the Injector. I have not found any specifications for the AC voltage or pulse duration for either the Ignition at pin 27 or Injector at pin 21 of the ECU. I measured both of these signals while cranking the engine, I got ~0.1 VAC at the injector, and basically zero (0.004 VAC) at the ignition module output. These numbers lead me to believe that the output drivers for these functions are damaged or dead, although I can see no signs of physical damage, no burnt smell, melted traces, cracks, or corrosion anywhere in the ecu components. Is there any function programmed in the ECU which would completely shut down the spark- and injector-outputs based on some combination of other inputs for some safety reason ? Any info on the specific layout of components relating to the Ignition and Injector Drivers in the 1987-1990 ECU would be greatly appreciated! And Thank You to all who have gone before me here, the info trail has been invaluable!! -
Here is 1987-90 Jeep YJ Wrangler and Jeep XJ Cherokee/MJ Comanche 2.5L TBI diagnostics information in PDF form. The first document includes all sensor and switch tests plus adjustments that affect engine tune, idle and reliability. Wiring schematics and ECU pin locations, test plugs and diagnostics included. Jeep 2.5L TBI Complete Diagnostics-Sensors-Switches.pdf Jeep 2.5L TBI ECU Inputs and Outputs.pdf Jeep 2.5L TBI MAP Sensor Test.pdf Jeep 2.5L Timing Chain and Tensioner.pdf Jeep 2.5L Valve Timing Check.pdf Jeep YJ 2.5L TBI Sensors and Pinout.pdf YJ Wrangler 2.5L TBI Wiring of WOT to ECU.pdf Jeep YJ 2.5L ISA Wiring Diagram.pdf 1987-90 2.5L TBI Intake Manifold and Sensors.pdf 1987-90 YJ Wrangler 2.5L TBI Emissions System Parts.pdf YJ Wrangler Fuel Filter and Guard.pdf 2.5L TBI ISA Motor Adjustment.pdf Used in conjunction with the many forum exchanges (search under "All Content" and "2.5L TBI" in the search box), plus the Jeep 2.5L TBI troubleshooting article at the magazine website, this information will help solve your Jeep YJ Wrangler or XJ Cherokee 2.5L TBI troubles. In references, the Model 81 is the Jeep YJ Wrangler. The Model 60/70 is the XJ Cherokee and MJ Comanche Pickup. Moses -
I put a new 2.5l into the jeep and it only has 400 miles. It was running great till suddenly the issues popped up again. I hooked the scanner up and saw that the short term trim was ridiculously high. Its reference point at idle is 128 and its running at 180. The long term trim is at 109. the injector pulse is 2.0. The o2 sensor was reading no higher than 500mv. -
Thanks for the engine information. Ok .... update for today. I'm really not finding a vacuum leak and before I build a smoke machine there's been this gnawing in the back of my mind to check the valve timing. I found this pdf manual http://oljeep.com/JeepEngines.pdf and on page 63 it tell how to check valve timing. So I removed all the plug, it was easier to rotate by removing all the rocker bridges, set up a dial indicator on the #1 intake push rod and checked .... Hmmm the dial moved .010 but I don't see the index mark anywhere (????) ... oh, there it is 3 inches to the left, or 3 inches BTDC ... really???? Guess I'll pull the timing cover and check it out.
