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12-23-2017, 11:44 AM | #1 | |
AF Regular
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1991 Wrangler 2.5 no start
What tells the fuel pump relay to shut off? I’ve got a YJ no start, fuel pressure does not build. The relay will click over on key on, and will the energize after two seconds, as if it’s expecting the fuel pressure is already high and it’s just topping it off a bit. Is there a sensor that measures fuel pressure and tells the relay to shut off? Or could this be a problem with the pressure regulator? I didn’t put a gauge on the rail because it’s at my other house 40 mins away and I can tell the pressure is literally zero, no fuel even squirts out schraeder valve.
Thanks much, Alex
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2008 Tahoe SSV, 2007 Tahoe SSV, 94 GMC K1500, 93 Chev K1500, 91 GMC K1500, 2000 Wrangler Sport |
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12-23-2017, 03:08 PM | #2 | |
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Re: 1991 Wrangler 2.5 no start
Worried I may be chasing my tail on this. There is good spark from the coil but weak spark from the cap. Dist cap and rotor replaced when I noticed this. Still not fixed. Could be bad pickup coil?
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2008 Tahoe SSV, 2007 Tahoe SSV, 94 GMC K1500, 93 Chev K1500, 91 GMC K1500, 2000 Wrangler Sport |
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12-23-2017, 06:08 PM | #3 | |
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Re: 1991 Wrangler 2.5 no start
If you have no fuel psi that needs addressed. Try spraying starter fluid in the intake see if it will run on that. If yes jump the relay to power the fuel pump.
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12-24-2017, 04:56 PM | #4 | ||
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Re: 1991 Wrangler 2.5 no start
Quote:
Thanks for info. Had already tried jumping the pump relay, still will not start. This morning, however, I hooked up a fuel pressure tester. While cranking pressure builds up to around 40 psi, but once cranking is done, it drops precipitously to zero. Thinking it was a problem with the fuel rail-mounted pressure regulator, I clamped off the return line, expecting pressure to maintain. To my surprise, pressure dropped just as fast. Incidentally, i thought this was especially strange given that when I previously directed the return line to a container, fuel came flowing out when I jumpered the fuel pump relay. Ruling out other possibilities, i really don’t think the injectors are that leaky. I took them off to test and at most a drip or two *may* have escaped one or two of them. This rapid fuel pressure drop has me at a loss. Is there supposed to be a check valve in the fuel pump that prevents this? Spraying some starter fluid in it can get it to start occasionally, but it dies a split second later. Thanks, Alex
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12-30-2017, 01:01 PM | #5 | ||
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Re: 1991 Wrangler 2.5 no start
Quote:
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12-30-2017, 02:16 PM | #6 | |
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Re: 1991 Wrangler 2.5 no start
Ok, been doing extensive troubleshooting over the last few days and am still somewhat stumped.
Here’s what I know: 1) spark was good from coil but weak to the spark plugs. Replaced the distributor + pickup coil and plug wires. Solved that problem. Timed the dist rotor to TDC on #1 cylinder, verified twice. Also, ignition coil and cps are new. 2) fuel pressure is good while cranking (I.e., steady at 40 psi) but drops off when key off - not sure if this is normal or not but with that good pressure at injectors while cranking should be good for a start. 3) compression is good (I.e., 120 psi) on all 4 cylinders. 4) Vacuum is bad. Flutters rapidly between 0-5 inHg while cranking. Starting to suspect that I may have a timing chain that has jumped a cog here, thoughts?
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12-31-2017, 10:26 AM | #7 | |
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Re: 1991 Wrangler 2.5 no start
You can use WD-40 and spray along edges of intake manifold while cranking. If you find a leak replace the gasket.
Get a long 1/2 drive ratcket with a socket that fits on the bolt for the harmonic balancer. Turn 180 degrees then align the timing mark at 0 degrees. Pull the distributor cap use white out and mark the rotor tip. Assuming you turned clockwise now turn counter clockwise stop when the rotor starts to move anything over about 10 degrees will cause problems. |
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01-01-2018, 12:43 PM | #8 | ||
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Re: 1991 Wrangler 2.5 no start
Quote:
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01-03-2018, 08:28 PM | #9 | |
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Re: 1991 Wrangler 2.5 no start
Well...took off the timing cover and this is what I found: the camshaft sprocket was completely stripped (teeth were stumps); the chain tensioner was limp and no longer sprung; the chain guide was missing and guide supports were machined away (apparently by the chain); and the camshaft and crank sprockets were misaligned.
Rotating the crank by hand I clearly witnessed the chain slipping over the cam sprocket. Will replace the sprockets, chain, tensioner, and guide and also drop the oil pan to empty out the probable debris within. I’ll report back with the outcome! (Edit): I should clarify that The cam was not frozen. It still rotated (and I still get good compression) but The chain would slip every now and then. Could not the absence of the chain tensioner for an extended period eventually wear down the Cam teeth and cause this issue? Also, this morning I pulled off the valve cover and rotated the cam by hand to witness valve operation and everything appeared normal
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2008 Tahoe SSV, 2007 Tahoe SSV, 94 GMC K1500, 93 Chev K1500, 91 GMC K1500, 2000 Wrangler Sport Last edited by ASJT3; 01-04-2018 at 06:33 AM. |
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01-10-2018, 09:57 AM | #10 | |
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Re: 1991 Wrangler 2.5 no start
Replacement of the timing chain and sprockets solved the problem. Thank you to everyone for their help!
By the way, I did not end up replacing the fuel pump. Can anyone confirm that for these pre-1997 2.5L, the fuel pressure does not maintain in the rail after shutdown? As noted previously, It builds fine to 40 psi while cranking and running but then drops precipitously during following shutdown. My sense is that this is normal behavior since the rail-mounted fuel pressure regulator appears to be basically just a flow restrictor and not an actual valve. Alex
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01-10-2018, 05:10 PM | #11 | |
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Re: 1991 Wrangler 2.5 no start
Generally they are located in the fuel pump. Some have had the hose leak between the top of the fuel pump and the outlet. This is about 3 inches long use 100psi high pressure hose. O'Reilly sell Gates high pressure hose. I would purchase a new sock or filter for the fuel pump if trying this procedure.
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