89 4.0 started this morning won't start now

[oldgoat]

Pretty vague I know but here is the rest.

 

89 4.0 AT basically stock.

 

Previous to today it sometimes takes several seconds, to minutes of cranking to get it to fire, other times fires right off.

 

I replaced the CPS today after it would not start.

 

The last couple of days I have experienced , "boil over" out of the surge tank. It has always started right up though.

 

Today I replaced the thermostat and refilled the coolant. Started right up and ran great until the stat opened then I had the "boil over" issue again.

Shut the engine off and let it cool, added more coolant.

 

After about an hour I attempted to restart, it will crank but won't fire. Fuel is to the rail and under pressure. After about 10 seconds of cranking I get a very slight "pop" as if it wants to start.

 

I can't prove that I have spark. Plugs are dry. I did try starting fluid with no success.

 

Yes, coolant went everywhere and most of the connections and relays got wet.

 

Digging further I found a heavy orange wire paired to a lighter orange/black stripe wire going to one of the relays that has the insulation melted off of it back into the harness about 4". It appears that this has been the case for a long time.

 

Any ideas?

 

Is there a way to hotwire the ignition system to validate that it works?

 

I haven't been able to find a clear wiring diagram for the 4 relays adjacent to the coil or the distributor wiring code.

 

 

 

 

[gogmorgo]

Can't speak for the Renix, as I don't know what's in the relay block (or even if there is one) but I've started my HO using jumper wires from the battery to the ignition and starter relays in the main relay block.

 

Check for spark by sticking a screwdriver into the end of a spark plug wire and holding the shaft 1/8" or so away from a bare metal surface that connects to ground, like a head bolt or something. You should be able to see it spark while a helper attempts to start the engine. It's easier to see the spark in the dark, of course. You can also do this for the coil wire to check the coil.

[oldgoat]

I didn't have a helper today, so I couldn't verify some things. There is always tomorrow.

 

I guess one additional question.

 

From the research I see, the distributor doesn't actually create a signal to fire the coil. Is that signal generated by the CPS? Is it the same signal used to fire the injectors?

[cruiser54]

Get a 703-1396 coolant bottle cap on there before you overheat the engine.

 

Click on the link in my signature and do Tips 1,3,4, and 5. 

 

CPS can be tested and modified as needed using Tip 7.

 

You can unplug the distributor's little harness and it will still run. 

[oldgoat]

OK, here is what I have learned so far.

 

This morning when I started I had nothing for spark at the coil.

The plugs were dry, so I must assume the injectors were not firing.

 

1 -  Repaired the burnt wires I mentioned in the beginning.

 

2 - Removed the coil and ICU, cleaned the contacts per Cruisers recommendation.

 

3 -  Replaced the battery to engine ground with a "00" cable and added a 2 ga cable from the dipstick stud to the body ground point.

 

4 - Checked the new CPS and found .17 - .22 volts cranking. I did the mod and now I see .27 - .38 , not great but better.

 

I buttoned everything up and tried to start. I got a series of pops like it wanted to start.

 

I pulled all plugs (first time since acquiring the truck) 5 of 6 were loose to the point that the threads were wet with fuel as were 4 of 6 on the tip.

 

Tomorrow I will replace the plugs and bring home a new surge tank and cap.

 

What might I be missing?

[cruiser54]

OK, here is what I have learned so far.

 

This morning when I started I had nothing for spark at the coil.

The plugs were dry, so I must assume the injectors were not firing.

 

1 -  Repaired the burnt wires I mentioned in the beginning.

 

2 - Removed the coil and ICU, cleaned the contacts per Cruisers recommendation.

 

3 -  Replaced the battery to engine ground with a "00" cable and added a 2 ga cable from the dipstick stud to the body ground point.

 

4 - Checked the new CPS and found .17 - .22 volts cranking. I did the mod and now I see .27 - .38 , not great but better.

 

I buttoned everything up and tried to start. I got a series of pops like it wanted to start.

 

I pulled all plugs (first time since acquiring the truck) 5 of 6 were loose to the point that the threads were wet with fuel as were 4 of 6 on the tip.

 

Tomorrow I will replace the plugs and bring home a new surge tank and cap.

 

What might I be missing?

You're missing performing normal maintenance like new plugs, wires, cap and rotor. 

[oldgoat]

Cap rotor and wires were recently replaced. Obviously plugs were neglected.

I have validated the cap and rotor. Wires are a question mark.

[cruiser54]

Lots of cheapo wires out there. 

[Marine1Texas]

Yes make Sure you get the brass cap n rotor. Like Cruiser said not all wires are equal. I like normally get accell 8.5mm blues for all my trucks. Make sure to also check you wire coming from coil to cap, seen bad ones that can cause issues.

 

I did not see if you checked spark. As Cruiser tips check your coil pack and make sure the leads are clean of corrosion. With your blow over it can cause problems with connections.

[cruiser54]

Taylor makes awesome wires also. Summit carries them. 

[oldgoat]

I originally had no spark from the coil.

I did replace plugs, wires, cap, rotor and the coolant tank and cap.

 

Gave it a crank and got some popping, tried again sames result. One more time and it did fire, ran rough and smoked to beat the band.

Settled out and ran smooth as glass.

 

Now to answer the mystery. What was it that caused it not to start after it had been running for about 30 minutes without a hitch less than an hour previous.

I really hate throwing parts and labor at an unknown root cause.

[cruiser54]

Couple of things.

 

First, check the integrity of the throttle body to MAP hose/tube.

 

Check the electrical connector on the MAP.

 

You MAY have some injectors that are leaking down when not energized. I prefer using the volvo 746 injectors as replacements.

[oldgoat]

Similar to the FP regulator signal being low. I will look at both.

 

I did notice that 2 injectors seem to be weeping from the o-riing at the rail.

 

I will say that the fuel economy is lousy and it always has a strong rich odor.

 

Is the MAP responsive enough that if I hook my mighty vac to it I can make an influence? What range does it really operate within. I have a 2 BAR on my blown LS that is very sensitive.

[cruiser54]

Ditch those original injectors in favor or volvo 746s no matter what.

[oldgoat]

What is a good resource for the injectors?

[cruiser54]

Contact Programbo on Cherokee Forum. 

[oldgoat]

I did discover a very small crack in the plastic tube going to the MAP sensor. Replaced the tubing, seems to run somewhat smoother and more consistent.

[cruiser54]

I did discover a very small crack in the plastic tube going to the MAP sensor. Replaced the tubing, seems to run somewhat smoother and more consistent.

Yup. 

 

Are your intake manifold bolts a bit loose? 

[oldgoat]

I will check that this weekend.

Are the rubber blocks that the MAP tube plugs into at the TB available. The one I have is less than great.

[cruiser54]

I will check that this weekend.

Are the rubber blocks that the MAP tube plugs into at the TB available. The one I have is less than great.

Only used. I'm working on a writeup to eliminate that rubber fitting. 

 

I'll tell you this though. If you remove the throttle body and tap the hole in it to 1/8 NPT, you can buy a fitting to screw into it.....

 

Here's the rough draft of Tip 29. I was planning on including part numbers where the parentheses are. If you want to do this and provide some photos and part numbers, along with any other suggestions, please feel free to help.

 

 

 

The Renix throttle bodies have a strange and failure prone connector on the side where the MAP supply originates and then runs up to the MAP sensor located on the firewall. This hose/pipe assembly is no longer available for purchase. 

 

The real kicker here is how critical this line is in supplying the correct vacuum signal to the MAP, the most relied upon sensor for the ECU to read regarding air/fuel ratio. Any cracks, melted spots, or loose rubber connectors can cause driveability issues. 

 

There’s a simple fix though. All that’s required is a 1/8” NPT tap, a new throttle body gasket (    ), and a vacuum fitting (    ). 

 

Remove the throttle body and take it to the workbench.

 

Using an oiled tap along with a driver, carefully thread the lower of the 2 holes of the throttle body. Don’t go too deep. These are pipe threads.

 

Flush the hole with carb cleaner and inspect for any left over cuttings.

 

Take the vacuum fitting (  ) and put a LITTLE sealer on the threads. I prefer Permatex #2 but almost anything is fine. Avoid RTV.

 

Carefully screw the fitting in until snug. 

 

Now you may need to replace the pipe up to the MAP sensor. Always use a rigid pipe like plastic as the original was, and route it running uphill to the MAP sensor. Some folks even use xyz metal brake line. The plastic pipe can be bent to fit using a hair dryer to heat it before bending it. Use flexible vacuum hose (   ) at each end to attach the pipe. 

 

This is an excellent time to do a complete throttle body and IAC cleaning. See Tip 11.

[oldgoat]

I probably have a 1/8 npt x 1/8 or 3/16 nipple in my brass collection. If time allows tomorrow I will perform the mod. Tomorrows big plan is really to work on finally re-doing the audio system in my GTO.

[oldgoat]

Is there a way to test the ICU?

Truck started just fine this morning, I went about 1.5 miles and it shut off just like you turned off the switch. Won't restart, no fire at the coil. I have fuel.

Pretty much the way things progressed last week.

 

Any other ideas?

[cruiser54]

Test the CPS output when this happens again. 

[oldgoat]

CPS is varying from .42 to almost .6 after I readjusted.

I get absolutely nothing for coil output.

The Yellow to coil + shows battery voltage.

I did put a test light from the yellow to the green/white which I believe is coil signal from the ECU. I don't see a flash in the test light while cranking.

[cruiser54]

May not see a flash. It's a square wave signal. Try a known good ICU/ coil.