jerking during acceleration?

I have a 1990 cherokee and it idles fine but when I accelerate It starts jerking back and forth. It just started today going to work. I'm kind of confused so if anybody has an idea let me know.

A 1990 is the last year with an EGR- probably not that, since it causes most trouble at idle/low rpm, runs fine at higher rpms. Three likely candidates: O2 sensor, Throttle Position Sensor, or inadequate fuel supply (could be either a plugged up fuel filter or a failing pump). If it is the O2 sensor, then it may be shorted- try a reading across the two wires (unplug it, check at the plug). From my files: Oxygen Sensor -
Located in the exhaust manifold. To test, using an ohmmeter, disconnect the O2 sensor connector. Connect the ohmmeter test leads to connector terminals A and B of the sensor connector. Resistance should be between 5 and 7 ohms. Replace the sensor is the ohmmeter displays and infinite reading. I don't know about you, but this test is pretty vague. They say it should be between 5 and 7 ohms, but infinite is bad. What if you get a reading of 13 ohms or 100 for that matter? I wasn't too fond of this test as I found it is a test of the O2 sensor heating element!. One other thing you can do with the O2 sensor is hook up the voltmeter to terminals B and C (I can't remember if those are the right letters, but you want to get the sensor wire (believe it was blue) and the ground wire, or just ground to something else) with the connector hooked up and the engine on, warm, and idling. You should notice the voltage jumping up and down in about 2 second or less intervals. If it doesn't jump up and down considerably or takes longer than 2 seconds to do so, change it.
If it is the TPS, then you should notice some weird (wrong time) shifts if you have an auto tranny, and you will have intermittent high idle (these are the symptoms on my 1990 with 4.0 engine/automatic--on third TPS since new). For the fuel pump/filter, you need to stick a gauge on the pressure valve at the front of the fuel rail, and see if it keeps the pressure up as you raise the rpms. You should have 30 to 40 psi- can't remember the exact number. If pressure drops at higher rpms, check for the fuel pressure regulator function (the small can at the front end of the fuel rail). Try clamping the rubber return line: if these leads to holding pressure at higher rpm, then the regulator is faulty. If this doesn't help, then the filter or pump are the cause of the lower pressure.
Also- electrical supply for the fuel pump: make sure that the white ballast resistor (on the fender in front of the air box) is well connected and not cracked. Those are the things I would look at first.
Most basic: how are the spark plugs/wires cap and rotor? I hope you have checked these!!

Is it an engine miss or a jerking in the steering? Motor mounts and tranny mounts can give you some unusual sensations on accelerating.

'Could be any or all of the above. Maybe bad cap/rotor/wires/plugs? TPS is very likely. 02, not in my experience with Renix but I haven't seen it all. Hell, just a bad ground on the engine/firewall can create this business. The injector connectors on these sometimes act like a plug wire miss too. Get a FSM and start checking wiring/connectors and sensors.

I had the same problem with my '89 XJ when I first got it. I thought it was the transmission or something in the drive train for sure. I put in a new O2 sensor and it cleared the problem up right away. So if you haven't put a new sensor in it is worth the time.

Burley

The problem seems to be the engine. The idle was seemingly fine now its idling really rough and the rpm is going hay wire. I checked spark plugs, wires cap and roter and everything seems fine. I was wondering if anybody knows how to test the oxygen sensor? Also I was going to check the fuel filter but I have to decompress it and I don't have the special tool. Chiltons manual says to disconnect the fuel pump relay from the PDC module. I can't find the PDC where its suppost to be under the hood. Does a 1990 not have one? By the way thanks for the great suggestions.

Still sounds like an O2 to me. There is no good way to test an O2 sensor. There life expectancy is about 75,000 miles if I remember correctly, so if it is around that old you should put a new one in anyway. You'll save a little on gas with a new one and from what I understand, a bad O2 sensor will trash your catalytic converter.

Burley

I will put the o2 sensor in then. Most of the testing methods that I've read about didn't really make sense to me either I think they all pretty much suck. I put in a new cap and a filter and it just hesitates to start so its probably the o2. Ill post back after I install it

mudagainstmachine said:

I will put the o2 sensor in then. Most of the testing methods that I've read about didn't really make sense to me either I think they all pretty much suck. I put in a new cap and a filter and it just hesitates to start so its probably the o2. Ill post back after I install it

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I'm just a backyard mechanic but I have been around electronic test equipment for about 16 years and know that to read resistance accurately under 10 ohms you need a high dollar ohm meter and not something you buy at the local parts store.

Let us know how you make out.

Burley

Renix 02 is not a low-voltage sensor like many later designs. It's output switching can be seen with practically any DVM using volt scale (back-probed into the connector) I've used. If you're easily amused you can wire a permanent set of leads into the cabin to test while driving around.

I've replaced 3 02's in my '89 over 180k miles. Not one caused any bucking/misfire engine driveability condition when they went bad. The only symptom (besides failing SMOG) displayed is/was erratic idle RPM. It idled smoothly just "hunted" for a HOT idle speed more with a bad 02. Oh yeah, the mileage dropped too.

Hesitates to start? LOL... Renix does that. 5-7 seconds cranking when cold is not unusual. Less for subsequent warm/HOT restarts.

Knowing what I've learned about Renix during 10 years, for stumbling/misfire-like conditions I'd be checking out the TPS, MAP vacuum lines and injector connectors.

XJXJ said:

Renix 02 is not a low-voltage sensor like many later designs. It's output switching can be seen with practically any DVM using volt scale (back-probed into the connector) I've used. If you're easily amused you can wire a permanent set of leads into the cabin to test while driving around.

I've replaced 3 02's in my '89 over 180k miles. Not one caused any bucking/misfire engine driveability condition when they went bad. The only symptom (besides failing SMOG) displayed is/was erratic idle RPM. It idled smoothly just "hunted" for a HOT idle speed more with a bad 02. Oh yeah, the mileage dropped too.

Hesitates to start? LOL... Renix does that. 5-7 seconds cranking when cold is not unusual. Less for subsequent warm/HOT restarts.

Knowing what I've learned about Renix during 10 years, for stumbling/misfire-like conditions I'd be checking out the TPS, MAP vacuum lines and injector connectors.

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I am having the same symptoms on my jeep and have a 02 sensor fault code. After reading this thread, I was hoping that would be it. You say this sympton is not caused by the 02 sensor..

pull up your pants and stop getting excited when your 4.0 takes of with all the mad torque!!!!





j/k i couldn't resist good luck, sorry i had to

Huerito said:

You say this sympton is not caused by the 02 sensor..

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No, this is a chat thread and ANYTHING offered is only a best-guess based on very limited information. What I'm saying is that I've replace 3qty Renix 02 sensors in 10+ years driving 180k miles. Not a single one caused drastic driveability issues like misfire and/or severe stumbling when they were on the way out. Based on that and my other experiences, I'd be looking in the TPS/MAP/injector areas for described symptoms with a Renix ECU.

Also, if you can retrieve codes I'm guessing you have a later-model XJ and not a Renix. This thread is about Renix and they are an old but durable design although much different from later OBD Chrysler MPI. If your ECU reports a bad 02, it should be replaced. Don't forget to clear ECU memory afterwards.

It wasn't the o2 sensor. I found ou that the distributors bad. I had spark early on but when it wouldn't turn I spark check it again and there was nothing. The coils fine and I just replaced the cap and roter. So I checked the distributor with the multimeter and it didn't check out.