'89 XJ shuts off after starting

[8Mud]

Why not try unplugging a couple of vacuum lines from the front vacuum tree and see what happens. See if it will run and stay running.
Mine runs (kind of) with the MAP electrical connector disconnected. It just runs really rich.
Or take your IAC out, gently and with feeling (better yet use your old IAC) push the piston in about 3/16 ". Reinstall it and and try a start.
What you are describing, sounds like your IAC is stuck shut and you need some air to get it going.
Actually you are supposed to compress (close) the piston down some when installing a new IAC. There was a warning about this way back when, if you don't, you can possibly bend the IAC piston rod. Most of the manufacturers, deliver them partialy closed/compressed, but who knows for sure.

 

[serge]

If your fuel pressure is low, unpluging the MAP could keep it running. Could be a bad pump or a pluged filter letting enough fuel through to start but not enough to reu.

Actually, I've done a fuel pressure test yet. I hear the pump kick in every time without any weird noises, plus it supplies enough fuel in the "hacked" mode, so I never bothered. Maybe I should get myself one of those pressure gauges. Also, I haven't replaced the fuel filter for 40K miles, so maybe it's time ....

 

[serge]

Why not try unplugging a couple of vacuum lines from the front vacuum tree and see what happens. See if it will run and stay running.

Ok, I've unplugged one by one several vacuum lines off the intake manifold and Jeep will still shutdown. While I was doing this, I've discovered something that is putting the "not enough air" theory in doubt. I unplug the vacuum line off the MAP and make the Jeep run. I hear the air being sucked into the line with a loud wistle. Now, if I plug the vacuum line with a thumb cutting off air intake -- guess, what -- there is not change in engine operation. So, it is not air that is the problem?

Something else I've tried that points to air not being the problem. With engine pretty warm, I very slowly try to put the vacuum line onto the MAP sensor. As I do that, the RPMs increase to approximately to 2K then come down to around 150. If the engine is not warm enough, it will shut off. If it is warm, it will work, but idle at 150 is a step away from shutoff. Now, if I play with the gas pedal, engine doesn't sound right and will backfire if I push the pedal fast enough.
What would make the engine idle so low?

BTW, EGR is exculpated. I've verified that the valve is normally closed and is not stuck open. Also, if unplug the vaccuum tube off the EGR transducer and pull air in, the valve will open (and kill the idling engine right away).

Where should I look next? I've checked all the sensors out and all of them are functional...

 

[8Mud]

BTW, EGR is exculpated. I've verified that the valve is normally closed and is not stuck open. Also, if unplug the vacuum tube off the EGR transducer and pull air in, the valve will open (and kill the idling engine right away).

I'm not really understanding. The EGR is spring loaded holding the piston seated between the exhaust and the intake. The EGR solenoid is normally open when not energized and supplies vacuum through the transducer to the EGR. The EGR solenoid is activated by the ECU and shuts off the vacuum supply through the transducer to the EGR. I'm not exactly sure what the transducer does, either some kind of vacuum amplifier or an additional input during lower vacuum operation or both.
What can go wrong with an EGR, the spring gets weak and the EGR opens too soon. Bucking during lower RPM acceleration.
The piston between the exhaust manifold and the intake manifold gets deposits on it and doesn't close all the way.
The diaphragm in the EGR ruptures, makes a vacuum leak, possible high/rough idle.
EGR is open during low RPM operation or cold motor operation. Engine barley runs and/or stalls, sometime backfires through the intake.
No power (actually ground through the ECU) to the EGR solenoid, it defaults open and allows EGR to function when it shouldn't. Like at low RPM's or before the engine is warm.
Transducer vacuum leak, high idle/rough idle.

 

[serge]

I'm not really understanding. The EGR is spring loaded holding the piston seated between the exhaust and the intake. The EGR solenoid is normally open when not energized and supplies vacuum through the transducer to the EGR. The EGR solenoid is activated by the ECU and shuts off the vacuum supply through the transducer to the EGR. I'm not exactly sure what the transducer does, either some kind of vacuum amplifier or an additional input during lower vacuum operation or both.

I think the transducer allows exhaust backpressure to open EGR.

For my test, I've ruled out EGR completely by unplugging and closing the vacuum line that goes to it.

Also, forgot to post last night that I was trying to check fuel pressure at the rail, but the cap is stuck on to the schrader valve pretty good. Light application of pliers didn't help. I think I can remove it by force but will damage the cap. Can I just replace that aluminum cap with a matching plastic one? Also, what do you make off my experiments with the vacuum lines?

 

[8Mud]

You need fuel, air and spark to make it at least pop. From your description, it sounds like you have spark (hopefully sharp and blue). So I'm thinking too little air or too much fuel or too little fuel.
When you pull the MAP vacuum line to get it running, does the exhaust look like it's running rich. If it's running rich, the exhaust usually smells of fuel and is fairly dark (soot). When the motor first starts up, it's in open loop, so the MAP inputs are important.
Have you checked the cam position sensor? Have you tested the MAP (and MAP circuit). Is your O2 sensor plugged in. I've found bent and backed out pins in the connectors before. I'd hook a voltmeter up to the fuel circuit and watch it during start and after the key is released to the run position and see if the voltage falls off. If your ballast resistor is jumped, the voltage should actually go up, when the starter is released.
Just for the heck of it, I would try holding the throttle open a crack and working the arm for the TPS a little (with a screw driver) just to see what happens. I've never seen it, but it seems possible the TPS (or the circuit) is faulty and The TPS is giving a deceleration reading to the ECU.
Have you ever been able to urge it into a higher RPM band, if much of the trouble disappears above say 1500 RPM, that tells a lot.
It doesn't sound like we are any closer to a solution.
Possibilities are a sensor out of wack (or a sensor wiring circuit). Low fuel pressure. The EGR hanging open, it will hang open, even though there is no vacuum to it. I've had to close them with a pair of needle nose pliers and they didn't close easy.
You mentioned once you could kind of coax it to life, by working the throttle. This is an indication of too little air. A fuel pressure test sure can't hurt.
The book says, fuel pressure above 39 PSI, dirty air filter, leaky fuel injectors, faulty O2 sensor or circuit, faulty EGR or circuit. Or possibly the motor is being fooled into the decelration mode.
By the way, my book says the transducer is a *delay* for full vacuum operation.

 

[langer1]

I think the transducer allows exhaust backpressure to open EGR.

For my test, I've ruled out EGR completely by unplugging and closing the vacuum line that goes to it.

Also, forgot to post last night that I was trying to check fuel pressure at the rail, but the cap is stuck on to the schrader valve pretty good. Light application of pliers didn't help. I think I can remove it by force but will damage the cap. Can I just replace that aluminum cap with a matching plastic one? Also, what do you make off my experiments with the vacuum lines?

Pulling the vacuum line off the MAP does one main thing, it opens the injectors wide open. The little extra air don't amount to much.
You still need to check that fuel pressure.

 

[serge]

Pulling the vacuum line off the MAP does one main thing, it opens the injectors wide open. The little extra air don't amount to much.
You still need to check that fuel pressure.

Ok, I've procured an Actron fuel pressure testing kit over the weekend. With key turned on, I've had 39psi at the rail instantly. The pressure held at 39 while cranking, when motor started and when it would shutdown. When I pulled the vacuum line of the MAP sensor (to get the engine to stay running) and engine would idle for some time, the pressure would drop to ~29 psi. According to the Renix manual, this is due to pressure regulator letting return valve open a little, since intake vacuum of -10 psi helps to "pull" the fuel in. If vacuum line was pulled off the pressure regulator, pressure at the rail would return to 39 psi. Looks like the fuel system works without a hitch.

 

[serge]

When you pull the MAP vacuum line to get it running, does the exhaust look like it's running rich. If it's running rich, the exhaust usually smells of fuel and is fairly dark (soot).

Yes, with vacuum line off the MAP Sensor, it runs, but rich.

Have you checked the cam position sensor?

No -- since I have spark, I've assumed I do not have to do that.

Have you tested the MAP (and MAP circuit).

With key "on", I read .5V on the output. According to the manual, this is the lowest acceptable value. This is as far as I've gone with testing the MAP Sensor. I've read a couple of other posts and I think I am making a mistake of assuming that the sensor works, because I got it "new" at the autoparts store. Tonite I will perform a more thorough check of it. Last night, while I was checking fuel pressure and had the engine running, I've tried to put the vacuum line onto the sensor slowly. While I was doing that, the engine was revving up really high and as soon as the line was completely on the sensore -- the engine died. I will check the readings while this happens with a multimeter tonight.

Is your O2 sensor plugged in.

Yes.

 

[8Mud]

Cam position sensor, in the Renix it indexes the firing of the injectors. It has little or no influence on spark that I've ever noticed. It seems to mostly act up, when the cam position sensor is bad or unplugged and the battery has been disconnected for awhile. The motor runs, but poorly. The Renix will run (rather well) with all the plug wires one or two places off on the distributor cap, but I've never tested it with everything 180 out. You might want to do a TDC 1 check, just to make sure. It might just as well turn out to be something basic.
Check the wires running down the front of the motor, from the front of the fuel rail, down to the engine temp sensor, the knock sensor and the O2 sensor. Closely
I saw almost the same thing once, the front harness was melted and the engine temp. sensor was shorted to itself. I'm guessing it was giving the motor an operating temperature reading at start up.
Check the wiring for resistance between the MAP and ECU, pay attention to the grey plug. I have found bent pins in this plug.
You have to make sure the EGR is closed, guessing won't do it, you have to physically pull it off and check it.
Check the heater circuit to your O2 sensor. The MAP pretty much runs the motor at start up, but (at least on mine) the O2 kicks in a lot quicker than the book suggests.
Few shortcuts have ever worked out for me, mostly it is plodding through the harness and testing sensors.
The grounds have given me more trouble than anything else, with corroded and/or oily connectors a close second. Scraping the paint away from the (firewall) head to firewall ground strap, was worth about 5-10 HP, by my butt dyno.
Good luck, my bet is it turns out to be something simple that has been overlooked. If it's multiple faults, that add up to the symptoms you are having, it can take awhile to plod through the whole thing.
For instance, when I first bought mine, it had a questionable O2 sensor, a bent pin in the MAP circuit, various grounds that were resistive, oil in the TPS plug, bad plug wires, a wet connector for the ICU power supply (line leak/low voltage). Melted front harness (about the fifth time I've seen that). Plugged fuel filter, a partially melted ballast resistor and other things. A jammed IAC and a plugged idle bypass circuit. Various vacuum leaks and a weak spring in the EGR. And other more minor stuff, like various resistive connectors in the sensor circuits. It took awhile to work the bugs out. But the motor started and ran, even with all the crap going on.

 

[serge]

Pulling the vacuum line off the MAP does one main thing, it opens the injectors wide open. The little extra air don't amount to much.
You still need to check that fuel pressure.

Ok, I've done a check of a MAP sensor operation with a voltmeter yesterday.
With vac. line on, I get ~4.5V on terminal B (I must have been checking the wrong terminal to get 0.5V previously). As soon as engine starts, the voltage drops to around ~2.5V (and engine dies). This behaviour seems to be inline with specifications. With VAC Line off, I get 4.5V on terminal B and it stays there, while engine keeps running. Also, the voltage will drop predictably if I try to slip the vacuum line onto a MAP sensor while engine is running. Yesterday, I've actually been able to keep the engine running (after it warmed up pretty well) when I slowly slipped the vac. line on. It idled at around 200 rpms, so it was close to death.

I'm almost ready to just accept the condition as is until I get my DRB II toolkit complete -- in hopes that it will give me some insight into the problem. In the meanwhile I came across this page http://go.jeep-xj.info/HowtoMAPsensor.htm. Has anybody tried this before?

 

[langer1]

Have you checked your timing? And have you tested your IAC or had it checked?

 

[serge]

Have you checked your timing? And have you tested your IAC or had it checked?

How do I check the timing -- by testing the CamPS? IAC is replaced with a verified new unit from NAPA. Swapping the old one with the new has no effect. I reset the computer in between as well.

 

[langer1]

How do I check the timing -- .

With a timing light.Where is the vacuum line for your MAP connected?

 

[serge]

With a timing light.

Something like this http://actron.com/product_detail.php?pid=16183?

Where is the vacuum line for your MAP connected?

Throttle body

 

[langer1]

Something like this http://actron.com/product_detail.php?pid=16183?


Throttle body

Like that.
Have we tested the TPS voltage yet?

 

[serge]

Like that.

Is there any difference between these units? Actron has other models too...

Have we tested the TPS voltage yet?

Yes, it was fairly low .5V. I've adjusted the TPS to read .8V (recommended value with closed throttle valve.

 

[langer1]

Is there any difference between these units? Actron has other models too...


Yes, it was fairly low .5V. I've adjusted the TPS to read .8V (recommended value with closed throttle valve.

Lets go back to that voltage at closed throttle.
Manual Transmission TPS all readings from ground (B)
A 4.75-5.0volts
B ground
C .85

AW4 Automatic Transmission TPS all readings from ground (B)
A 4.75-5.0 volts dc.
B ground
C 4.14 volts dc
As you can see Manual and Auto are opposite.
Manual starts low and goes high and Automatic is High and goes low.

 

[serge]

Lets go back to that voltage at closed throttle.
AW4 Automatic Transmission TPS all readings from ground (B)
A 4.75-5.0 volts dc.
B ground
C 4.14 volts dc
As you can see Manual and Auto are opposite.
Manual starts low and goes high and Automatic is High and goes low.

I have AW4. The .8V reading was for the ECU Connector. When I did the adjustment, I did so on the TCU connector. Just for kicks, I wanted to check what was the ECU end reading, and got .8V. According to the manual, this is an ideal value.

 

[langer1]

I have AW4. The .8V reading was for the ECU Connector. When I did the adjustment, I did so on the TCU connector. Just for kicks, I wanted to check what was the ECU end reading, and got .8V. According to the manual, this is an ideal value.

I have quoted the renix FSM the readings your quoting is for the manual transmission.
The automatic version is not the same as the Manual, the readings are at the tps connector.

The TPS for the manual is a singal unit (3 wires) the TPS for Automatic is a dual unit (6 wires) the three closest to the TB is the ECU wires a.b.c. the outer is the TCU wires d.e.f.