HELP!!? 87 RENIX 4.0 long crank/long start
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Joined: Aug 2011
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From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
So, for all the naysayers, I went and got a full tank of gas. But, I had to start it with starting fluid to get to the gas station. After I got gas, I let it sit overnight and went to start it this morning and nothing, nada, zilch. It starts just fine on starting fluid. After it starts with the starting fluid it runs just fine and dandy. So, I know I'm getting fuel and spark.
I'm just not sure why it won't start without starting fluid. I did some searching and found this link, http://www.xjtalk.com/showthread.php?t=5907.
Here's a quote from the thread. =
[("If you have both spark and fuel pressure, the problem can only be a couple of things. Most commonly, the engine is flooded and the plugs are wet, but it could be a timing problem. Crank it for a few seconds, then go smell the tailpipe. Do you smell gas? If so, the injectors are most likely working and the fuel system is fine. There are only three sensors on the Renix system that will cause a no start condition. The most common is the CPS, surprisingly the second is the MAP sensor. Make sure the hardline from the throttle body runs to the MAP and that the MAP is plugged in. Plug and unplug the MAP connector a couple of times for good measure.)
(If you haven’t been screwing with the ignition and could not have indexed the distributor incorrectly, and you have spark and fuel pressure after having made sure the plugs aren’t wet, the engine should start. If it simply never fires, and you can smell at least a little raw gas in the exhaust, timing is pretty much the only thing left other than the injectors not firing. To test the lack of fuel in the cylinders scenario, have a buddy crank the engine and squirt a little starting fluid down the throttel body. If it tries to fire, the injectors are not giving you any gas. If that doesn't get an attempt to fire up it is probably back to the timing issue. If you have done the CPS routine, then you either have a bad camshaft sensor, bad computer, or bad wiring. It is possible that the coil is so weak that it will spark the plugs when they are not under compression, but doesn’t have enough power to spark under compression. The ECU is probably the least common, followed by the cam position sensor, and the coil. (GROUNDING straps are also good to check at this point)]
So, with this info, I'm thinking it's possibly the Camshaft Position Sensor/Pickup Coil/Stator, whatever you wanna call it.
What are y'alls thoughts?
I'm just not sure why it won't start without starting fluid. I did some searching and found this link, http://www.xjtalk.com/showthread.php?t=5907.
Here's a quote from the thread. =
[("If you have both spark and fuel pressure, the problem can only be a couple of things. Most commonly, the engine is flooded and the plugs are wet, but it could be a timing problem. Crank it for a few seconds, then go smell the tailpipe. Do you smell gas? If so, the injectors are most likely working and the fuel system is fine. There are only three sensors on the Renix system that will cause a no start condition. The most common is the CPS, surprisingly the second is the MAP sensor. Make sure the hardline from the throttle body runs to the MAP and that the MAP is plugged in. Plug and unplug the MAP connector a couple of times for good measure.)
(If you haven’t been screwing with the ignition and could not have indexed the distributor incorrectly, and you have spark and fuel pressure after having made sure the plugs aren’t wet, the engine should start. If it simply never fires, and you can smell at least a little raw gas in the exhaust, timing is pretty much the only thing left other than the injectors not firing. To test the lack of fuel in the cylinders scenario, have a buddy crank the engine and squirt a little starting fluid down the throttel body. If it tries to fire, the injectors are not giving you any gas. If that doesn't get an attempt to fire up it is probably back to the timing issue. If you have done the CPS routine, then you either have a bad camshaft sensor, bad computer, or bad wiring. It is possible that the coil is so weak that it will spark the plugs when they are not under compression, but doesn’t have enough power to spark under compression. The ECU is probably the least common, followed by the cam position sensor, and the coil. (GROUNDING straps are also good to check at this point)]
So, with this info, I'm thinking it's possibly the Camshaft Position Sensor/Pickup Coil/Stator, whatever you wanna call it.
What are y'alls thoughts?
CF Veteran
Joined: Aug 2011
Posts: 10,489
Likes: 24
From: Nor-Cal Coast
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
A few things:
Did you try the "poor mans prime" Turning the ign. on, then off three or so times, 3 seconds apart, before turning to start?
Do you hear the pump run a couple of seconds when you turn the ign on? (note that with the ignition on, you can jump Bat. power to the rear of the resistor and try it)
Last. The pump gets power for a a few seconds from the relay when you turn ign on. Also it gets power from the relay after it starts. BUT! while it's cranking, it needs power from the start relay! Is that top left terminal hot while it's cranking? Is that wire good to the resistor? (Meaning the front of the resistor is hot while it's cranking, I suppose)(I mean it might go to the rear)
See diagram below. (or in my sig)
Did you try the "poor mans prime" Turning the ign. on, then off three or so times, 3 seconds apart, before turning to start?
Do you hear the pump run a couple of seconds when you turn the ign on? (note that with the ignition on, you can jump Bat. power to the rear of the resistor and try it)
Last. The pump gets power for a a few seconds from the relay when you turn ign on. Also it gets power from the relay after it starts. BUT! while it's cranking, it needs power from the start relay! Is that top left terminal hot while it's cranking? Is that wire good to the resistor? (Meaning the front of the resistor is hot while it's cranking, I suppose)(I mean it might go to the rear)
See diagram below. (or in my sig)
Thread Starter
Seasoned Member
Joined: Jul 2012
Posts: 312
Likes: 0
From: Little Elm, TX
Year: 1987
Model: Cherokee
Engine: Inline 6 cylinder
Oh, I should've mentioned. I checked the voltage to the fuel pump while cranking, it was getting voltage. I just don't remember how much. And yes, it runs after turning the key on. Also, I have no fuel pump ballast resistor, so no top left terminal.
CF Veteran
Joined: Aug 2011
Posts: 10,489
Likes: 24
From: Nor-Cal Coast
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
Hadn't thought about that. Got my doubts they changed the starter relay when they added the resistor though. I suppose in your shoes I'd be curious if it had that terminal, and if it's connected to the pump. The fuel pump relay won't juice the pump until the ECU get's a signal from the cps. For sure the ECU will not ground the fuel pump Relay until it turns a couple of revs at 300 RPM, and maybe not until it's running.
Senior Member
Joined: May 2012
Posts: 925
Likes: 6
From: Fort Erie, CANADA
Year: 1987
Model: Cherokee
Engine: 4.0
As one of the naysayers, I'm glad you got gas. That rules out the basic problem. It starts on starting fluid so again, Yay! Also, it runs fine once started on starting fluid so you can stop messing with timing, injectors, coil, spark plugs etc (as mentioned many posts ago). If you're systematic, the root cause should become apparent-You may have to work backwards now-Ask what the difference is between a starting problem and a running problem-you no longer have a running problem (you can actually drive it).
So, things that other guys could help out with are things that might effect engine running on start up-I'm not sure that all of these would stop your engine from running from a cold start.
-aftermarket alarm system?
-bad ignition switch
-bad relay
-bad ECU (unlikely)
-bad coolant temp sensor (used for determining air/fuel mixture)
-bad MAT sensor (used for determining air/fuel mixture)
A lot of this can be checked with an ohm-meter. If you know of anyone that has a SNAP ON MT-2500 scan tool (the brick model) it would help you run down a lot of things quickly so you can see what your ECU is seeing and trying to change.
So, things that other guys could help out with are things that might effect engine running on start up-I'm not sure that all of these would stop your engine from running from a cold start.
-aftermarket alarm system?
-bad ignition switch
-bad relay
-bad ECU (unlikely)
-bad coolant temp sensor (used for determining air/fuel mixture)
-bad MAT sensor (used for determining air/fuel mixture)
A lot of this can be checked with an ohm-meter. If you know of anyone that has a SNAP ON MT-2500 scan tool (the brick model) it would help you run down a lot of things quickly so you can see what your ECU is seeing and trying to change.
Thread Starter
Seasoned Member
Joined: Jul 2012
Posts: 312
Likes: 0
From: Little Elm, TX
Year: 1987
Model: Cherokee
Engine: Inline 6 cylinder
No alarm system. I have two ECU's. But this problem happens on both of them. Coolant temp sensor shouldn't have anything to do with it starting cold, guess it couldn't hurt to replace it though. The MAT is also know as the IAT right?
Thread Starter
Seasoned Member
Joined: Jul 2012
Posts: 312
Likes: 0
From: Little Elm, TX
Year: 1987
Model: Cherokee
Engine: Inline 6 cylinder
I don't know if this has anything to do with it or not. But, I noticed the spark coming from the Coil isn't blue and snappy anymore.
Senior Member
Joined: May 2012
Posts: 925
Likes: 6
From: Fort Erie, CANADA
Year: 1987
Model: Cherokee
Engine: 4.0
I don't know if this has anything to do with it or not. But, I noticed the spark coming from the Coil isn't blue and snappy anymore.
No alarm system. I have two ECU's. But this problem happens on both of them. Coolant temp sensor shouldn't have anything to do with it starting cold, guess it couldn't hurt to replace it though. The MAT is also know as the IAT right?
No alarm system. I have two ECU's. But this problem happens on both of them. Coolant temp sensor shouldn't have anything to do with it starting cold, guess it couldn't hurt to replace it though. The MAT is also know as the IAT right?
The temperature sensors tell the ECU to enrich or lean the fuel mixture based on the engine temp and incoming air temp-that's why I thought it would be something to check to make sure it's sending the right ohms to your ECU for start up . Probably not too cold in Texas though. The CTS is in the rad, the MAT is in the manifold. Easy to check-Don't replace them until you've used your meter.
CF Veteran
Joined: Aug 2011
Posts: 10,489
Likes: 24
From: Nor-Cal Coast
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
My not exactly un educated guess is that the IAT , (incoming air Temp) might only matter in some some sub 0* condition. It's a minor player. (I just have a 200 ohm resistor on one of mine) And it doesn't care if I don't.
Coil test aside, I wonder how much power the pump is getting while it cranks. That could be it.
Coil test aside, I wonder how much power the pump is getting while it cranks. That could be it.
Senior Member
Joined: Nov 2014
Posts: 603
Likes: 1
From: Hacienda Heights
Year: 1990
Model: Cherokee
Engine: 4.0
Not true. If the spark is weak while cranking it may still be enough to fire ether vapor but not enough to fire gasoline, especially since it won't be well atomized. Once running the system voltage goes up substantially so there's a possibility of a stronger spark combined with the better atomization of running speed making it easier for that spark to do it's job.
Senior Member
Joined: May 2012
Posts: 925
Likes: 6
From: Fort Erie, CANADA
Year: 1987
Model: Cherokee
Engine: 4.0
Not true. If the spark is weak while cranking it may still be enough to fire ether vapor but not enough to fire gasoline, especially since it won't be well atomized. Once running the system voltage goes up substantially so there's a possibility of a stronger spark combined with the better atomization of running speed making it easier for that spark to do it's job.
Senior Member
Joined: Nov 2014
Posts: 603
Likes: 1
From: Hacienda Heights
Year: 1990
Model: Cherokee
Engine: 4.0
It may start with a few plugs that are weak, but it may not if the whole system is. I haven't said his is a weak spark issue, but I will continue to say that it could be. I can't count how many times a spark issue has looked like a fuel problem; only starts on ether, only runs with the choke on, runs fine except under load,... Bad ballast resistor, bad coil, poor connections, bad coil wire, ect.; I've seen them all and in many cases it looked like a fuel problem or something else, I've seen it with gasoline and propane engines. Low compression can cause very similar results.
Ever had a plug that wouldn't fire with the wire plugged in but pulling the wire back so the spark has to jump to the spark plug terminal made it work? Some things just don't make no damn sense but living it repeatedly proves it possible.
Ever had a plug that wouldn't fire with the wire plugged in but pulling the wire back so the spark has to jump to the spark plug terminal made it work? Some things just don't make no damn sense but living it repeatedly proves it possible.