New motor will crank, but won't start

T

T_1776

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Oct 18, 2020
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Virginia
Hello,

My wife has a 1998 TJ with the 2.5L and a 5 speed. The #4 piston sleeve broke apart so the motor started knocking pretty good so we bought a remanufactured long block to throw in. I just finished buttoning up the swap and the engine will crank, but won't fire. I know this will be like finding a needle in a haystack with the amount of work I did, but I can eliminate a few things I've checked so far:

I verified the fuel pump kicks on and I have fuel at the line (checked Schrader valve), pulled codes and nothing. So I'm under the assumption spark is my issue. I did realign the distributor with cylinder #1 at tdc, checked fuses/relays, visually inspected grounds, verified all connections are good with one exception. The previous owner apparently broke and removed the connector on the harness side for the crankshaft position sensor. I've moved the wires around trying different combinations with no luck.

I'm guessing it is either the crankshaft position sensor connector or a ground somewhere... Does anyone have any other ideas I could try? I do need to pick up a new electrical tester as my old one is shot so I'll be able to start testing circuits soon.

Thanks in advance!
 
T_1776 said:
Hello,

My wife has a 1998 TJ with the 2.5L and a 5 speed. The #4 piston sleeve broke apart so the motor started knocking pretty good so we bought a remanufactured long block to throw in. I just finished buttoning up the swap and the engine will crank, but won't fire. I know this will be like finding a needle in a haystack with the amount of work I did, but I can eliminate a few things I've checked so far:

I verified the fuel pump kicks on and I have fuel at the line (checked Schrader valve), pulled codes and nothing. So I'm under the assumption spark is my issue. I did realign the distributor with cylinder #1 at tdc, checked fuses/relays, visually inspected grounds, verified all connections are good with one exception. The previous owner apparently broke and removed the connector on the harness side for the crankshaft position sensor. I've moved the wires around trying different combinations with no luck.

I'm guessing it is either the crankshaft position sensor connector or a ground somewhere... Does anyone have any other ideas I could try? I do need to pick up a new electrical tester as my old one is shot so I'll be able to start testing circuits soon.

Thanks in advance!
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Have you checked for spark? Either use a spark tester or just ground a spark plug to the block while you crank?

When you say the connector was removed for the CPS do you mean there is no connector or the factory wires were diked off & replaced?

Here's a snap from your factory service manual (available for free in the TJ Resources forum) that shows the pinout for that particular connector. Can you trace whatever wires are there back to the factory wires to make sure the colors line up? Pin 1 is grey/black/, pin 2 is brown/yellow, pin 3 is orange.

I think you should first verify what you DON'T have (spark, fuel, air, compression) & pick a direction to go. When you get your meter we can help you out finding grounds/ checking for power.

1603069102199.png
 
qslim said:
Have you checked for spark? Either use a spark tester or just ground a spark plug to the block while you crank?

When you say the connector was removed for the CPS do you mean there is no connector or the factory wires were diked off & replaced?

Here's a snap from your factory service manual (available for free in the TJ Resources forum) that shows the pinout for that particular connector. Can you trace whatever wires are there back to the factory wires to make sure the colors line up? Pin 1 is grey/black/, pin 2 is brown/yellow, pin 3 is orange.

I think you should first verify what you DON'T have (spark, fuel, air, compression) & pick a direction to go. When you get your meter we can help you out finding grounds/ checking for power.

View attachment 197103
Click to expand...

I appreciate the response! I meant to ground a spark plug yesterday, but plan on doing so after work today.

As for the CPS connector, based on the diagram you posted (thanks by the way) they replaced the wires and removed the connector leaving bare wires behind. I say that because the wire colors are as follows: green/red, green/white, and black/orange. But I will try to trace them back to see where he spliced these in.
 
Last night got away from me, but I was able to work on the jeep for a few minutes today. I was able to trace back the CPS wires a couple feet to find the original wire colors and have it connected according to the diagram.

Also, I was able to verify that I do not have spark; pulled a plug out and placed it near a few different grounding points for verification with the boot still attached and no luck when cranking.

Not sure if it's a grounding issue or what, but I'm running out of ideas.
 
You need the spark plug to make contact. The spark will jump the electrodes. If the plug is not grounded then there will be no spark! As for fuel, you should have something like 50-55 psi (IIRC) at the fuel rail. You can borrow a tester at most any parts store. But it sounds like the crank sensor is most likely to be the problem. Were there any other issues with the new motor install? Those are always the point to start at. Any chance you could be 180* off on your distributor (assuming you have 1)? Do you have an actual code reader or just getting code from the odometer?
 
T_1776 said:
Yeah I checked beforehand while it was still on the engine stand. Thanks though!
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Can you describe how exactly you checked it?

It has to be at tdc on the compression stroke as opposed to being at tdc on the exhaust stroke.

Obvious to most but just making sure to check the easy/obvious stuff first.

After that, the CPS wiring seems like an obvious suspect.
 
Goatman said:
You need the spark plug to make contact. The spark will jump the electrodes. If the plug is not grounded then there will be no spark! As for fuel, you should have something like 50-55 psi (IIRC) at the fuel rail. You can borrow a tester at most any parts store. But it sounds like the crank sensor is most likely to be the problem. Were there any other issues with the new motor install? Those are always the point to start at. Any chance you could be 180* off on your distributor (assuming you have 1)? Do you have an actual code reader or just getting code from the odometer?
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I did the best I could to make a true "ground" connection by resting the spark plug threads/electrode on the block, the motor mount bracket on the frame side, and a couple different areas, but there is always a chance that this was not a 100% perfect test.

I will have to borrow a pressure gauge to verify the true pressure at the lines, will probably do that this weekend.

The rest of the build went perfect except a few busted knuckles, etc.

As for the distributor, I checked it against cylinder 1 and held my finger over the spark plug port while turning the crank to verify pressure was coming out of the cylinder. Correct me if I'm wrong, but that to me says the piston was on the compression stroke. But with this being the only time I've ever really messed with a distributor to this extent, it could be out 180 deg. Any other way I can verify that?

I do have an actual code reader, but nothing as of yesterday.

I really do appreciate all the insight and advice guys!
 
g.hayduke said:
Can you describe how exactly you checked it?

It has to be at tdc on the compression stroke as opposed to being at tdc on the exhaust stroke.

Obvious to most but just making sure to check the easy/obvious stuff first.

After that, the CPS wiring seems like an obvious suspect.
Click to expand...
That is a great point actually. I only checked based off timing chain and cam sprockets. But for the sake of my own sanity, I truly hope this isn't the case....

I may get a new CPS connector on the harness side and replace the sensor just to be safe.
 
A few updates on this: put in a new CPS, no luck. Verified that I have no spark, my wife cranked while I held the plug in the boot with fuel pump relay removed. Traced back a bit and found that I have 0.14V to the ignition coil.... from my understanding, I should have 12V. With that new info, I'm leaning towards a bad ground somewhere. I have a ground for body to frame, frame to motor, and alternator to motor (at least I think it connects to the back of the alternator, too dark out and flashlight died). Both ground connections on the motor are at the ignition coil, still researching to verify that this is the correct location for these. I did find that I have a bad ground at the large stud on the back of the motor that connects to the firewall, so essentially I'm missing the body to motor ground. By bad I mean that the actual eyelet broke and is barely making a connection. I'm wondering if this is the reason why I'm getting 0.14V instead of 12V or 0V at the coil.

Also checked the ASD pins and have power to pins 85 and 30 only. If I remember correctly, I should have power to 3 pins and not 2.

Any other suggestions?
 
Seems like every time this comes up in similar situations it's bad timing at the chain, or distributor alignment.
I know I struggled with it for a bit before on my old YJ.
 
707kevin said:
Seems like every time this comes up in similar situations it's bad timing at the chain, or distributor alignment.
I know I struggled with it for a bit before on my old YJ.
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I appreciate the quick response! I thought about both of those options quite a bit as they've been mentioned above from other members, but the only issue I have with those options is that even if either of those were the case, shouldn't I still have spark? Or at least 12V to the ignition coil? I'm pretty green when it comes to distributors, but I don't see how either engine timing or distributor alignment would kill power to the coil. Although either would prevent the motor from firing. I don't mean to come off like a dick and apologize if I do!
 
Check fuse 21 which is for the ign coil. You can then use the ohm meter function of your meter from fuse 21 to the ign coil connector pin 1.
 
T_1776 said:
I appreciate the quick response! I thought about both of those options quite a bit as they've been mentioned above from other members, but the only issue I have with those options is that even if either of those were the case, shouldn't I still have spark? Or at least 12V to the ignition coil? I'm pretty green when it comes to distributors, but I don't see how either engine timing or distributor alignment would kill power to the coil. Although either would prevent the motor from firing. I don't mean to come off like a dick and apologize if I do!
Click to expand...

You're right! I was on my cell at work and didn't catch that part.
 
Well I replaced the bad ground wire and removed and cleaned up the other grounds just to be sure. I also checked the resistance between fuse 21 (ign coil) and the connector with 0.1 ohms. Doesn't seem like enough resistance to cause an issue to me, but I'm not sure. I'm still getting anywhere from 0.05V - 0.14V at the ignition coil connector. I'm really trying to avoid paying a mechanic to come out here, but I don't know what else to check.
 
.1 ohms is a good resistance reading.

So if I'm hearing you right (&going by the diagram below) you aren't getting any voltage at pin 1 of the ignition coil connector. Are you checking with the ignition in the 'run' position? The ASD relay should be closed when the ignition switch is in the run position, providing battery voltage to fuse #21 through connector C103 & down to the ignition coil.

1605380365211.png
 
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qslim said:
.1 ohms is a good resistance reading.

So if I'm hearing you right (&going by the diagram below) you aren't getting any voltage at pin 1 of the ignition coil connector. Are you checking with the ignition in the 'run' position? The ASD relay should be closed when the ignition switch is in the run position, providing battery voltage to fuse #21 through connector C103 & down to the ignition coil.

View attachment 203480
Click to expand...

Well I feel like a bit of a fool, but I didn't realize that the ASD relay also killed power to the coil after 1-2 seconds of turning the key... I had my wife turn the key while I checked and sure enough, I get 12.5V-13V for a short time and then it drops. I went back to the crankshaft position sensor and verified that I was getting 5V to the sensor. But... I unintentionally hit the sensor wire as well and was surprised/scared when I saw that I was also getting 5V from the signal wire as well! From my understanding, I should see something from the signal wire only while cranking due to the way the sensor operates, but I'm getting 5V from both the supply and signal wires with the key on (not cranking). I figured there had to be a short somewhere so I traced the wires back to the PCM with no obvious issues. Out of desperation, I opened the PCM as well to check the capacitors and/or for any burn marks in general, but no dice. I took pictures of the internals to be on the safe side, but I'm throwing in the towel for the night.

I can't thank you guys enough for the support and advice, it is greatly appreciated!
 
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