88 comanche hard start or no start when cold

[Ωhm]

@silvertwinkiehobo Upper right hand of screen. Click on Username. Click on Account Settings. Find and click on Signature. Add vehicle information here (YR, ENG, TRANS, etc, etc) and save. This helps everyone. This information will be available every time you post.

[cruiser54]

I know the one you mean. 

 

Make sure the STOP screw is adjusted properly FIRST. Then, readjust the TPS per my Tip ONLY if you moved the STOP screw. 

Then, with it warmed up and idling as good as it gets, unplug the IAC and turn that screw to get a stable idle at about 850 RPM.

[silvertwinkiehobo]

Thank you. I had thought it was an idle bypass adjustment screw, but I didn't want to find out I was wrong. I did a visual on the throttle plate (which we cleaned last Summer), and it appears to be not held open with carbon. So I'll follow your directions. BTW, earlier, while the truck was idling high at operating temperature, the exhaust smelled rich. A thought occured to me about a possible problem with the ECT, so I'll be rooting that out tomorrow. I'm going on the possibility the ECT is bad or the wiring is open, causing the computer to think it's always cold outside.

[silvertwinkiehobo]

Never mind about the diagram, I finally found one. I'll try to remember to snap pics to post.

[silvertwinkiehobo]

So, went through Cruiser54's Renix page, and using the instructions he listed here, I fixed the sensor ground wiring, then made the throttle stop, TPS (WAAAAY the feck off, <450mv), and with the IAC disconnected, adjusted the idle air bleed a ways out to get the 850 RPMs (after the TPS adjustment, Idle was under 500 and barely idling) adjustments. So, we put a chrome front bumper on (see pics), gonna chase fuel and oil leaks, and may chase a possible rear axle bearing noise, which might just be the new tires anyway.

[cruiser54]

EXCELLENT!!!

[silvertwinkiehobo]

After a couple days of cold low idle speed, Joe got a new IAC, installed it, and now she idles up on initial start, and has a better idle quality and speed, cold or hot. Cruiser, your instructions are a godsend, as I tried finding any info on the throttle body in Joe's factory XJ manual (AMC), and found very little. Joe's now floating the idea of A/C, as a recent freeway trip to San Antonio was quite loud and windy, but I had to bring him back to Planet Earth on all his and my other wheeled projects....🥵

[cruiser54]

Thanks for the update!!

[ctxj93]

Unfortunately, I'm still battling this issue. I found my intermittent no start condition was caused by a loose pin in the fuel pump connector, but I still have a long crank on cold starts. 

 

At this point I have indexed the distributor again, replaced the map sensor line, tested the MAT and coolant temp sensors, and tested vacuum and compression.  I've also adjusted the throttle stop and reset the TPS.  Compression is 130-140 on all cylinders and holds 18 inches of vacuum at idle. Plugs are a little sooty, but not horrible. I'm still not sure if the IAC is working as intended. 

I have cleaned all my grounds and added an additional ground from the neg battery terminal to the body while I waited for my JeepCables order to show up. They will be installed this weekend. 

 

After reading through the fuel injection manual again, I came across this page (attached). Is it possible that the ecu isnt receiving a sync signal, and after enough crank time just picks an injector as described? It says it will probably start but not well. Could something be hooked up wrong it's and causing the ecu to not receive a signal? Would it still run if that were the case? 

 

A cold start these days usually takes 2- 5 second crank cycles. It would probably start on the first crank if I continued to hold the key for another 5 seconds.  Once the jeep has run for even a minute, it starts perfectly every time for the rest of the day.  However, if I try to start it cold again a day or so later, I'm right back to square 1. 

 

I'm trying to get my hands on a snap on brick to see if I can glean any info from what the sensors are reading while its running, but I feel like I'm  running out of leads to chase here! 

[87MJTIM]

You have to get Nickintimedesign's REM.

 

This will allow you to monitor your engine while it is running under load.

[ctxj93]

2 minutes ago, 87MJTIM said:

You have to get Nickintimedesign's REM.

 

This will allow you to monitor your engine while it is running under load.

I have one on order!

 

I should add that it doesnt stumble to life like it used to. Once it finally starts, it revs up and settles down like normal.  I also found the evap line from the tank was hooked directly to a fitting on the intake manifold.  The PO removed the charcoal canister, but I replaced it and fixed the hose routing. I'm sure getting a direct suckle on fuel vapors was doing wonders for the air/fuel mix. 

[Ωhm]

RENIX 4.0L's I think has a normal CRANK time between 7-9 seconds. Engine must reach a least 350-400rpms before the ECU can even start to think about STARTING. Both battery and starter condition come into play here. Don't touch the gas pedal while CRANKING.

[cruiser54]

Yup^^.

[ctxj93]

9 minutes ago, Ωhm said:

RENIX 4.0L's I think has a normal CRANK time between 7-9 seconds. Engine must reach a least 350-400rpms before the ECU can even start to think about STARTING. Both battery and starter condition come into play here. Don't touch the gas pedal while CRANKING.

I must've been lucky with my last 2 renixes, they always fired right up quickly. I've never actually measured the crank time, I'll see if I can get a real number on it. Starter seems to crank over at a normal rate. Maybe  I'll take a video of the next cold start and you guys can let me know what you think.  Thanks again for the help!

[cruiser54]

There are some other factors to consider.

One is the fuel system losing it's prime overnight.

 

try this to see if it may play a part. Key On for 10 seconds, key Off, Key On for 10seconds and then to Start. 

[Eagle]

8 hours ago, Ωhm said:

RENIX 4.0L's I think has a normal CRANK time between 7-9 seconds. Engine must reach a least 350-400rpms before the ECU can even start to think about STARTING. Both battery and starter condition come into play here. Don't touch the gas pedal while CRANKING.

 

Yes. A 5-second crank-to-fire time in a Renix MJ or XJ would be considered fast.

[ctxj93]

10 hours ago, cruiser54 said:

There are some other factors to consider.

One is the fuel system losing it's prime overnight.

 

try this to see if it may play a part. Key On for 10 seconds, key Off, Key On for 10seconds and then to Start. 

I will give it a try. When I did my fuel pressure testing I walked away for a few hours and had minimal pressure drop. In the process of trying to figure out the no start problem, I swapped the pump from my old reliable (fast starting) comanche as well.  I can hear the pump prime when I turn the key, is that not enough to fully pressurize the rail?  Typically if I try multiple key cycles, I won't hear the pump run on the second turn, like the system has reached it's desired pressure. 

[cruiser54]

Coupla hours versus overnight is a lot of time for injectors to leak down. 

[Ωhm]

1 hour ago, ctxj93 said:

Typically if I try multiple key cycles, I won't hear the pump run on the second turn, like the system has reached it's desired pressure.

The ECU is senseless of fuel line pressure. It will always pick the Fuel Pump Relay for 2-3 seconds at KEY ON.

[cruiser54]

This^^

[ctxj93]

5 hours ago, Ωhm said:

The ECU is senseless of fuel line pressure. It will always pick the Fuel Pump Relay for 2-3 seconds at KEY ON.

I sort of figured that was the case.  

 

And cruiser, I agree. Totally possible my injectors are leaking down. It's  been sitting about 24 hours now. When I go try it in a bit, I'll see if there's any residual pressure at the shrader valve before cycling the key 

[ctxj93]

https://youtu.be/HBdwS-HrPNA

 

So after 24ish hours I had just a little dribble of fuel come out of the shrader valve.  As suggested this was 10 seconds key on, off, 10 seconds on, Start.  Any thoughts? 

 

And before anyone comments, yes I wish I had a few more missile switches. (Not my doing) 

[Ωhm]

2 hours ago, ctxj93 said:

Any thoughts? 

 

Typical cold start.

[cruiser54]

confused. Dribble before or after key cycling? 

[ctxj93]

19 minutes ago, cruiser54 said:

confused. Dribble before or after key cycling? 

Before cycling.  After sitting overnight I checked to see what kind of residual pressure was in the rail, and just got a few dribbles. Like a puddle no bigger than a penny on the intake.