Jeep 4.0 No Start HELP!

85TrailRunner

85TrailRunner

Member
Joined
Mar 16, 2007
Location
Monroe
Alright so I've put in the rebuilt engine back into my '98 Jeep Grand Cherokee thats been sitting for 3.5 years. The engine will spin over but won't start. I've checked the distributor's timing & it appears to be good, I've checked for fire from the spark plug wires & they're firing, & I've even replaced the spark plugs just to be on the safe side. I have removed the fuel tank & dumped the old fuel from it & checked the empty tank for debris. I removed the valve core from the fuel rail's test point & let the fuel pump run several times to get the old fuel out of the fuel lines. I checked the fuel rail & fuel injectors & made sure they were free of old fuel & spraying also. And still the Grand Cherokee won't start, it'll spin over great & act like it REALLY wants to for a few seconds but it just won't.

What could possibly be the problem that I'm overlooking here? I haven't tested the actual fuel pressure yet but last time I checked when the old spark plugs were still in the engine they were getting fuel to them, should I check fuel pressure to make sure it is getting constant pressure? Any help would be greatly appreciated, thanks!
 
Crank position sensor is usually the culprit. They are notorious. I went through a similar troubleshooting on my 96 cherokee and I can't stand shotgun approaches to fixing cars so I commend you for not throwing parts at it like some. You can test the crank ps with an analog voltmeter if memory serves me correctly.
 
Well after a suggestion from a guy at work of putting half an oil cap of oil into each cyclinder to help with compression after a rebuild(I knew to do so when testing for compression by checking compression then adding oil to see if compression gets better & letting you know the condition of the piston rings) via the spark plug hole I checked the compression for each cylinder.

1 - 90psi
2 - 90psi
3 - 100psi
4 - 140psi
5 - 60psi
6 - 100psi

Haynes manual says spec is 120-150psi & a max of 30psi variation from the highest reading so if my readings are right then I'm way off from spec. I was using a Craftsman compression tester that I haven't used before so I don't really know how accurate it is, I do have a cheapo from Harbor Freight so I'll recheck compression to verify the first readings. The guy that did the rebuild is well known in the area & I know several people that have used him on different occasions & had nothing but great things to say.

I'll look for a test on the crankshaft position sensor, thanks for the idea because I'm willing to test/try anything to get it to crank at this point. Any more suggestions?
 
Alright, had a buddy come over to veryify what I was doing what right & we retested my timing & it was good. Still getting fuel to the spark plugs like before. Engine spins over fine. Hooked a timing light to the #1 spark plug wire & with the crankshaft pulley marked with engine TDC on compression stroke & the "0" on the engine block marked spun engine over & its not firing every time it should be. Checked spark with an in-line tester on all six cylinders & they're firing. So why is my timing act like its off even though distibutor's timing is spot on?

We tried testing the crankshaft position sensor & its getting the correct voltage from the pcm with the key on(spec is 5v & I'm getting 5.11v). When we hooked the connector from the wiring harness back to the connector for the cps & backprobed the connector on engine harness side & hand spun engine over & every so often all my relays click in the power distribution center under the hood, is that normal? When the relays click the voltage reading is anywhere from 1 - 5 volts & when the relays aren't clicking the voltage reading is 0 which the Haynes manual says its supposed to do, but the Haynes manual doesn't mention anything about the relays clicking when the voltage is present so is the relays clicking like that normal?

So despite the clicking the cps appears to be testing good per the Haynes manual although they said to use an analog multimeter & I've only got a digital so thats what I used. Anyone got any ideas or suggestions as to what to try?
 
might want to post this over at naxja. They're the experts. ;)
 
you said the timing was spot on? i thought i had mine perfect but my friend cranked it while i just turned the distributor by hand and sure enough it started right up. Just a suggestion, im sure you have prolly tried already though.
 
You really need a scan tool to see if the cam/crank signal is in sync. That will tell you for sure if the sensors are working properly and it is getting signal to the PCM. Did it run before just needed a engine rebuild? Did you replace any sensors during the rebuild? Did you airgap the crank sensor with a green dot on the tip during installation?
 
Yea it ran before it was rebuilt so I'd like to think stuff like the distributor cap, rotor button, & I would think the sensors would still be good but at this point who knows after it has sat for 3.5 years. All the sensors that were on the engine stayed on the engine when it went to get rebuilt so they could very well be messed up from reinstallation, so I honestly don't know if the crankshaft position sensor was put back in with the paper spacer or not to prevent damage. Does AutoZone or Advance Auto have scan tools that will read the sensors that they'll loan out or do I gotta buy one?
 
Try this. Get ur digital multimeter and put the probe to the sensor wire for the sensor. Put the meter up agains the window and go crank. You should see 5v and then the reading should blip back and forth to about 11v when you are cranking. If you don't see the blip and it stays at 5v then you probably have a bad sensor.
 
russ0943 said:
Try this. Get ur digital multimeter and put the probe to the sensor wire for the sensor. Put the meter up agains the window and go crank. You should see 5v and then the reading should blip back and forth to about 11v when you are cranking. If you don't see the blip and it stays at 5v then you probably have a bad sensor.
Click to expand...


I'll try it & post back, thanks.:beer:
 
X2 on the rotating the distributor while someone cranks the engine. I too was helping a buddy try to start his newly installed 4.0 and he had the timing set correctly. After much time relocating wires on the cap and spinning the distributor we finally got it to start. Setting the timing on those 4.0's is touchy.
 
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