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Old October 18th, 2005, 12:47
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slowrider slowrider is offline
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Fuel system help

I can't figure this one out so here goes. I have an 87 MJ with a 4.0 auto that has 180k on the OD. I just did the So Cal to Moab and back run (1500+Miles) and had no fuel issues but I had massive blowby of 1 qt per tank of gas through the air filter, no smoke from the tailpipe and milage of around 12.5 per gal. on the way back. Within the last 1,000 miles prior to the trip simply because the truck was new to me and I didn't know it's history I replaced the fuel filter and pump, plugs, wires cap & rotor, vibe dampner (seperating and squealing), rear main seal (big leak), oil pump (poor pressure),pan gasket and valve cover gasket. So I hadn't started it since returning from moab and it started OK but died within 1 minute, it restarts OK but won't run for more than 1 MIN. The fuel rail has pressure and squirts fuel about a foot if you hold the schrader valve open while starting. Any suggestions of what to do about the blowby or stalling issues would be greatly appreciated.

Last edited by slowrider; October 18th, 2005 at 12:48. Reason: mistake
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Old October 18th, 2005, 13:01
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Matthew Currie Matthew Currie is offline
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Re: Fuel system help

On the blowby. it's a pretty common problem with these. At some point, they modified the vacuum line for the crankcase vent, putting less sharp curves in it, and though that seems minor, it helps. You need to make sure that all lines are clear and clean, no cracked elbows, and the grommets are sealing properly, because if vacuum doesn't pull out from the back of the cover, the blowby will push out the front. It's also not uncommon to find the innards of the valve cover heavily caked with crud, obscuring the passages, so it might be worthwhile taking it off and cleaning it. Expect large blobs and crumbs of carbonaceous crud to fall out as you do this, and try not to let them fall into the oil passages of the head. As you probably know, this is a valveless setup, depending on balanced vacuum and a certain amount of wishful thinking to work properly.

I don't think 87's have a ballast resistor for the fuel pump, but yours might. If there is one, try bypassing it for the running problem. If there isn't one, I'm not sure what to try next.
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Old October 18th, 2005, 18:37
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slowrider slowrider is offline
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Re: Fuel system help

Thanks for the tips. I forgot to mention that I've been trying to find all my vecuume leaks for a while but the only thing I've done since Moab was to replace the grommet on the back of the valve cover and after that it started stalling.
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Old October 19th, 2005, 13:39
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GSequoia GSequoia is offline
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Re: Fuel system help

Okay here is how I'd start to go about this...

1: What about your Crankshaft Position Sensor? Those guys fail often and rule of thumb with a 4.0 and stalling problems is CPS. I'd give it a try; even if that's not the problem it's a damn good part to have lying around as spare. If that does not clear up the stalling let me know.

2: Blow by: I'd remove the valve cover and clean it up 'til it shines. Take apart the stuff inside the cover (you'll see it) and clean it liberally. When I did mine I used a few cans of Berryman's B-12 Chem Tool (the aresol varity) and a Dremil with a nylon brush attachment. With a little patience you can get it nice and cleaned up.

Next I would look into replacing all your vacuum lines (if you haven't alredy done so). You can find them sometimes at select Kragen stores, I've stumbled across them before much to my surprise in the Help! aisle; I'll keep my eye out to pick one up for you if you want. If they haven't been replaced yet those lines need it anyway as they'll be nice and brittle. You'll want the mess of lines unit, there are two halves to this, and the CCV lines - the single lines that goes from the top of the valve cover to the intake.

If you have any questions let me know.
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Old October 19th, 2005, 13:46
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5-90 5-90 is offline
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Re: Fuel system help

You can also get the vacuum line kit from NAPA - they'll have to order it, and it will cost you about $52 for all three parts of the set. Look for it in another post recently - I updated the pricing and the part numbers in NAPA/Belkamp are in there. Just ordered two sets myself.

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Old October 24th, 2005, 21:00
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slowrider slowrider is offline
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Re: Fuel system help

Thanks again for the help but no good so far. I checked the CPS and the wires going to it were so brittle they cracked when I examined them so I replaced it, idled longer the first time we started it but soon went back to stalling in less than a minute. Double checking the vacumme lines and found only one small issue with a line loose in the vacuume harness sealed it. no change. Next we tried testing the M.A.P. sensor which had 4.8 volts which is high middle of the range given by the Haynes manual which said the voltage should fluctuate with the RPM but on mine it just degrades from 4.8v to 1.7v, replaced the MAP sensor no difference????? Any more suggestions?
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Old October 25th, 2005, 01:12
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Dvipercop Dvipercop is offline
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Re: Fuel system help

As far as blowby goes, my suggestion is to replace the entire CCV system. I recently did this on my '92 XJ and it completely solved my blowby problems. Not sure exactly how different your MJ engine is from mine, but on mine the fitting that screws into the the intake manifold was blocked completely. Considering when clean it's only a pinhole anyhow, it doesn't take much to clog it. I bought the parts from a dealership for a 2000 XJ since they have a wider inside diameter on the rear hose and fitting. Only cost me 20 bucks total for all the hoses and elbows (I get the employee discount). Best $20 I've spent on my rig so far.
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