Help Quick!!! Won't run!!

[simonsxj]

I just got a 1989 XJ 4cyl. Put a new fuel pump in it and it ran great for while. Now I can crank it and it will try to fire, and run if I hold the throttle down, but very rough. The injector seems to be pumping out plenty of fuel (visibly, I don't have a psi gauge with me). If I unplug the injector for while it will run great, which indicates to me that it is running rich, the plugs look fowled out too. Now the problem is when I took the cap off the rotor and cap are very badly built up. My question is, can the rotor and cap and plugs be causing this? It drove fine for a while after the new fuel pump. Could the injector have gone bad and be pumping too much fuel into it. I know how to measure pulse width on the injector but I don't know the specs. Help this is my daily driver. PLEASE HELP!

 

[logdog]

Easiest thing first; fuel filter. Then move on to the plugs, wires, cap, rotor, ballast resistor, TPS, CPS..........

 

[simonsxj]

So you think it might be the filter that made the old pump go bad and although I can see fuel it might not be enough, good thinking. I guess I will just have to do a whole tune-up. Thanks.

 

[skipc]

I highly doubt the fuel filter!! A bad filter can REDUCE pressure, leading to a lean condition, not a rich condition. When you press the throttle to the floor on an 89, the computer stops firing the injectors. The fact that it will run, expectedly rough, like that, says too much fuel, as does having it run while pulling the injector wire.

Check the pressure regulator on the rail. If not that, then perhaps the new pump is bringing the system up to normal pressure and the faulty injector(s) are now leaking more than they were before.

Pull each injector wire, one at a time, and see which one is causing the problem. Also pull the vacuum line to the regulator first and see if there's fuel in it (a ruptured diaphragm).

 

[simonsxj]

TBI I don't think I even have a regulator. Having thought about it the cap and rotor are so bad I think it might just not be burning all of the fuel. Could this happen or am I dreaming, I mean the contacts have a good 1/16" of build up on them.

 

[skipc]

Your regulator is the can shape connected at the front end of the fuel rail with a vacuum line out of the end. I would check that the vacuum line is dry first, or disconnect it and see if fuel squirts out when you turn it on.

Crud under the cap might cause poor running, but probably not in the way you're experiencing. More misfiring (if it's conductive crud) or loss of power (if insulating crud). It also wouldn't respond to pulling the injector wire like yours did.

 

[simonsxj]

Skipc I thank you for the info but this is a TBI as in the injector is in the throttle body. There is no fuel rail that I can see. The line goes straight in the throttle body and the return line comes out of the throttle body.

 

[jneary]

i would check the o2 sensor. i had problems with a 89 2.5 tbi wrangler a long time ago. turns out that was the problem

 

[jneary]

if you want to test the injector, hook a timing light up and shine the light on the injector while running. it should spray a mist. if you see signs of gas dripping from the injector it is bad.

 

[tchase]

the first thing that you should do before you go too far is check the fuel pressure, it wouldnt be the first time a new part was faulty, or a clog was created by dusturbing the system.

 

[simonsxj]

I know that the o2 would be a good one to check, but how do you check it when the vehicle doesn't run? PLus would that make it run so rich that it would not run? Also I can visibly see gas going in, it is still a mist but I can see it without a timing light. Does the TBI have a fuel regulator? I just had a brain fart, the engine doesn't go into closed loop until it warms up, so it cannot be the O2.

 

[tchase]

if the problem ends up with your injestors, you might want to check the injector signal. you can do this with an pulse sentisve test light on the signal wire.

 

[jneary]

I just had a brain fart, the engine doesn't go into closed loop until it warms up, so it cannot be the O2.

then i guess you dont need my help.

 

[simonsxj]

Tchase thanks for the advise but as I stated earlier, I am getting too much fuel, can't be a clog. Also to check the injector you have to check it's pulse width, the light will only tell you that it is firing, I need to know for how long it is firing, I just don't have the specs I need to check it. I have a multimeter that has a pulse width setting. I just can't figure this one out. I think what I'll have to do is do the tune-up and see what happens. It may be the fact that before the pump was put in it was running lean and with a weak ignition. But now it has a richer mixture maybe the ignition can't burn through it and has allowed the plugs to foul. Does anyone out there think that this could happen or am I blowing smoke?

 

[tchase]

sometimes you fix something as simple as the brakes olny to have the starter go before it leaves the hoist. it is very possible that another component has failed.

 

[skipc]

Skipc I thank you for the info but this is a TBI as in the injector is in the throttle body. There is no fuel rail that I can see. The line goes straight in the throttle body and the return line comes out of the throttle body.

I should have caught the TBI in there, sorry. You STILL HAVE a pressure regulator though. It is on the TB about 90 degrees around the TB from the ISA motor. Looking down at it, it's 90 deg clockwise. The adjustment screw is on the bottom. It is a can-like shape and bolts on the TB with 3 screws.

I dont' have an internal diagram, but the FSM talks about it having an internal spring chamber, which the MPI ones do too.

My bet is on a leaky regulator or leaky o-ring seal since I believe it's fed internally and relies on those seals and they are in the air path. Perhaps the higher pressure from a new pump is blowing by them. There's a slight chance it's a leaky injector, but disconnecting it if it were leaky shoudl have gotten a different repsonse than you got.

All FI systems have some sort of regulator, since the injector delivery and measurement is dependent on fairly accurate pressure at the injector. It's just a matter of finding it.

Hope that helps, sorry for the confusion.

 

[skipc]

I just had a brain fart, the engine doesn't go into closed loop until it warms up, so it cannot be the O2.

:sure:

This is a common misconception, often cited as a reason for not lowering the thermostat temp. The system does NOT use coolant temp to go into closed loop. The goal, and it's related to the mfg passing their emissions qualification, is to go into closed loop as fast as possible. That's why the O2 sensor has a heater! If it didn't go into closed loop until the engine was hot, by then the exhaust would have been hot for some time and there would be no need for a heater.

The cycling of the O2 sensor is what triggers closed loop. In fact, the FSM says that in the absence of a valid temp signal, it will approximate the temp based on running time. This is because a cold engine needs a richer mixture to run smoothly (poor fuel vaporization). The Renix manual also states that if the O2 sensor stops cycling, it will go back into open loop mode. I've seen this numerous times with OBDII systems where you can watch it go into closed loop on the computer. It takes 1-2 minutes - as soon as the O2 sensor voltages start to move +/- it goes closed loop. The temp gauge hasn't moved yet!!

Pass it on... :lecture:

 

[simonsxj]

Vaild point, interesting I had forgot the use of heaters on them nowadays. I am still used to the old one wire. But still would it make the XJ run so rich it wouldn't run? Plus I still have no way of testing this without the vehicle running or do I? I remember from my school days that a reading of about 450 mv should be correct, is that correct? I am still going to do a tune up this morning. it needs one anyhow. I post the results.

 

[skipc]

The voltage should cycle back and forth from about .2 to .8 v fairly rapidly (every couple seconds maybe). These are approximate numbers as it's the result of the ECU adjusting mixture. If it just stays on one value, and it's hot, it's dead.

When cold, the ECU puts out a pre-programmed amount of fuel since it knows the pressure is constant from the regulator, and knows the injector, throttle position, engine speed. It also shuts off the injector when you press the pedal to the floor on start. You said that got it to run, although roughly. It does this so you can clear a flooded condition.

My estimate is that it is getting more fuel than it needs, and when you get it to shut off the injector, there's enough to make it start without the injector on. However, when it starts, you can't keep the injector off, so the preset fuel amount, plus the leak, make it run rough and rich. That fouls plugs too, which will make it worse.

The leak theory is almost certain with the fact that you can disconnect the injector and it still runs!!

So, look for fuel leaks in the path of a vacuum or intake path. That would be - leaky injector, leaky o-rings on the supply side of the injector (TBI model only), or pressure regulator (either model). See my note a few above on finding the TBI regulator.

Not sure how easy it is to loosen your TB, but try this. loosen the base bolts and remove the bolts. Lift enough to slide a piece of paper under it. Do this if you haven't tried starting in a while. Slide the paper under it so it covers the whole air path. Turn the key to run (NOT start), wait a few seconds, turn it off and do it again, etc, about 4 or 5 times. Don't crank it! Wait a minute and go pull the paper out. It should be dry. My guess is you'll have a big gas spot on it proving a leak. That should verify an o-ring or injector leak. The regulator is tougher since it's ports are inside the TB, but if they are bad enough it may show there too.

Then you'll have it narrowed down.:clap:

 

[Dave in Eugene]

Besides the obvious crappy dist. cap, rotor, and plugs as you mention (relatively cheap stuff that you already know need replaced), with your engine running rich from startup, in engine warmup mode the ECU is looking at coolant temp, air intake temp, MAP Sensor, speed, and knock sensor. MAP sensor is the main component that's going to set your air/fuel ratio.

Here is some info from the FSM (there are a couple of places about where you can download a bootleg FSM, zip files are 16-18 MB):
Make sure the vacuum hose to the MAP sensor is good, plus all the other vacuum hoses at the manifold. Then, with key on and not running, voltage at pin B of the MAP sensor should be 4.0 to 5.0 volts. Output voltage should drop 0.5 to 1.5 volts running warm at idle. This voltage should also be present at the other end of it's circuit, pin 33 at the ECU. Input voltage of 4.5 to 5.5 volts should be at pin C, via pin 16 of the ECU, and the remaining pin should be at ground, via pin 17 of the ECU. Sensor ground via pin 2 of the ECU is on the flywheel housing near the starter motor, and it wouldn't hurt to look at that. Sensor is probably a common GM sensor you could get at a junkyard for almost nothing, I think a new one is kind of expen$ive. I learned my 4.0 won't run at all without one so I grabbed a spare & put it in the toolbox.

MAP SENSOR <------------------------------------>ECU
4.0-5.0V pin B<<------------->>------------>>pin 33 (MAP Output)
4.5-5.5V pin C<<-------------<<------------>>pin 16 (MAP Input)
GROUND pin A<<-------------<<------------>>pin 17--pin 2<<-->>Sensor ground