Grandcherokee23432

I have a jeep grand cherokee 1995 Laredo v8 5.2ltr. The vehicle sat with half a tank of that ethanol crap gas in it. I put sea foam in tank and into vacuum line. Replaced spark plugs with champion plugs new fuel filter and it still shutters bad when i drive it 40-55 mph. If i slow down the jeep goes back to normal. I'm not sure if this is a fuel injector or if the throttle body may be clogged. Idles fine, i may be able to feel a slight hesitation in the motor. Since its a v8 im wondering if i just cant feel the misfire at low rpms. Please someone help me.

I know the mechanics on this forum are some of the best in the industry.

Thank you for all the help in advance.

Fyi. There is 229,000 miles on the vehicle. I have had it since 55k. There was no problem with the jeep when i stopped driving it.

wingless

How does the fuel look?

Using a fuel pressure gauge connected to the fuel rail, dump it into a glass jar, let it settle for hours to determine if it separates into water, fuel and alcohol.

It might be the transmission. How does the fluid look?

Bustedback

Did you replace the spark plug wires when you did the plugs?

wingless

Spark plug wires are easy to measure using a multimeter. They should measure ~4K to 10K Ohms. Also do a visual inspection on the rotor and cap.

dave1123

It sounds like the spark is being blown out by higher cylinder pressures whenever it gets under load. Usually this is caused by weak spark voltage or large spark plug gaps. You replaced the plugs so we can rule that out. You may be loosing voltage by shorting wires, carbon tracked boots or distributor cap and rotor shorts or large gaps. OR....it could be the coil. Pull the main coil wire out of the cap and set it up with a 3/8" gap to ground. Crank the engine and you should get a nice blue flash that you can hear. Test each spark plug lead the same way.

Bad gas may have something it do with it, but in that case, it would run crappy at idle too.

Grandcherokee23432

Yes Dave i think you are right its the cap rotor or coil. I'm going to put an ohm meter to it tomorrow. I will update tomorrow with my results. Thank you for the advice. I am also gong to do a compression test on all the cylinders tomorrow. For peace of mind. I know this jeep is a monster boss with a ton of power and i have babied it its entire life. She just needs a little attention right now. I left her alone to long and she is reminding me to drive her more.

Grandcherokee23432

OK i did the manual diagnostic turn ignition on off 5 times i received the following three codes. 21,27,32

Code 21-Oxygen sensor signal-neither rich or lean condition is detected from the oxygen sensor input.

Code 27-Injector control circuit-bank output driver stage does not respond properly to the control signal.
Code 27-Injectors No. 1, 2, or 3 control circuit and peak current not reached.

Code 32-Exhaust Gas Recirculation (ERG) solenoid circuit-open or short detected in the EGR solenoid circuit/EGR failure-required changed in fuel/air ratio not detected during diagnostic test.

i was smart enough to get the codes could someone tell me if they make sense and interpret them for me.

let me know what i need to do before i pull this distributor out. the distributor is in a very hard to reach spot due to the engine

Bustedback

I don't think you will have to pull the distributor. It looks like you have a dead O2 sensor and a failing PCM. Have you checked the charging system out? A weak charging system will cause some funky stuff to happen.

Grandcherokee23432

how would i check the charging system? check the alternator? I am going to take the pcm out of the jeep and clean all the connections tomorrow. I read on another forum a guy who checked all the wires going to the fuel ionjectors and pulled his pcm and cleaned all connections and a problem similar to mine went away after he did this and the jeep has sat for two years so water could have gooten in and made the connections bad

wingless

The three charging components that must all be intact and functional are the generator; the wiring and the regulator.

The FSM details how to inspect and test each component.

The generator should be capable of outputting 90A.

The regulation is provided by the PCM. The FSM testing defines that testing.

The wiring requires visual, mechanical and electrical testing.


What are the symptoms causing a charging concern?

Bustedback

The bucking and backfiring. Low voltage to the ignition can cause that.

dave1123

Also, a momentary interruption in the ignition, as in loose connections.

wingless

Measure the battery voltage w/ the engine off. It should be 12.6 VDC or greater for a fully charged battery.

Measure the battery voltage w/ the engine running. It should be 15.0 (at -40°F) to 13.25 (at 160°F).

With the engine running also measure the voltage at the fuse feeding the PCM. It should be very close to the battery voltage.

Grandcherokee23432

The battery is a week old marine/rv deep cycle battery. I will check it.

Grandcherokee23432

Battery is good alternator is good fuel pump and fuel regulator all tested well 50psi
PCM is good as well. I believe i have a bad injector im going to pull the injectors and the rail clean and reinstall them. Does anyone know how i can put power to the injector one at a time after they are removed and run cleaner through them and visually watch the spray from them?

Thank you all for the great insight and help. I knew the jeep forums would have the smart guys