renix--long crank time, stumbling/misfires when cold

[RaccoonJoe]

OK, 1990 XJ. 4.0/AW4/etc...

I recently bought a 1990 XJ. Picked it up because it had a "unfixable" overheating problem. Turned out to be a simple cap on the coolant bottle.

I replaced the bottle, then heater core, heater hoses, thermostat, and finally a full conversion to a open cooling system (new 2 row rad). Add in 6 new spark plugs + wires + air filter, and I took it on a 3 day, 1600 mile trip from Indiana to Conneticut and back.

The trip was uneventful. The jeep ran a bit cold, ~160 degrees. I'm going to call that as a thermostat which opens and never closes. Gas mileage was a bit low, but still around 20.

When the jeep was cold, (in the mornings) it would crank a bit longer than when warm. It also misfired for a few seconds, then would run like a champ.

After a few days of sitting outside getting some bodywork, I could barely get it to start this evening. When it did finally start, (after almost 45 seconds of solid cranking) it stumbled, misfired, and barely held a idle. It also blew a massive cloud of white smoke out the back.

Any ideas as to what I can do about this? Any ideas why this might be happening?

 

[birchlakeXJ]

Good link for general Renix troubleshooting below....

Gotta verify what your actual temperature is. Your gauge or sending unit may be providing inaccurate data. Get your hands on an infrared point and shoot thermometer and point it directly at the thermostat housing. Compare that to what you read on your gauge. You may not be at 160.

BTW, if you got 20 mpg on your trip, you're doing better than the majority of all XJ owners.

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

 

[joe_peters]

You are ruining the starter by cranking it that long.

Fully charge the battery (life begins at the battery) and have it load tested. You may be pulling the voltage too low during cranking for the electronics to function.

Battery fully charged and passed load test? Renew cable ends and grounds. Grounds at engine block, dipstick tube, back of head to firewall, and at the starter relay.

All done with that?

Check fuel pressure with a gauge.

Test the Coolant Temperature Sensor under the manifold DS of block, not the gauge sending unit at the back of the head.

 

[89xj]

could be a bad cps. if its the original cps than i would swap it out or atleast carryt it as a spare.

i would also do a fuel pressure test.

for the renix, a strong battery and upgraded battery cables can make a big difference at start up along with priming the pump for about 3 seconds before turning it over. did you replace the fuel filter?

hopefully it doesnt have a bad head gasket. you may want to do a compression test, especially if it had over heating problems.

 

[RaccoonJoe]

There were some overheating problems, that's actually how I got it so cheap. I have not changed fuel filter, but will def. investigate compression and fuel pressure numbers.

A friend also proposed a warped intake manifold or bad intake manifold gasket? The theory there was that it was sucking air into the cylinders, causing a lean condition....but when it warmed up due to exhaust gasses, it would expand and self-seal the leak, causing it to run OK. Any thoughts/opinions?

 

[RaccoonJoe]

OK. I did a coolant pressure test, trying to see if I would get any coolant accumulating in the cylinders. All I found was that the thermostat housing was leaking.....

I was curious, what's the spec for compression on a stock 90 4.0? Compression testing being done now....

 

[GrimmJeeper]

mine 86 MJ does the same thing, and ive got a 1000 CCA battery and 0g battery cables. it cranks right away, and fast, but takes about a good 10 seconds of cranking to fire. after that it stutters a couple times then smoothes out and runs like a champ. its got 231k miles on it and it gets 25mpg on the highway

i figure its just cause its an old engine. im going to put a new set of plugs in it and see if that helps.

 

[RaccoonJoe]

Well, the results are in. Compression tests came out mostly excellent. Cylinders 2, 3, 4, 6 are looking at 120 PSI of compression, +/- 10. Cylinder #5 has about 95 PSI, but cylinder #1 has only 58 PSI. Spark plugs are in good shape after about 1700 miles, they are slightly brown, with some oily residue at the top of the threads that smells extremely strongly of gasoline. Plugs have no sign (taste or smell) of coolant, and no cylinder is cleaner than the next (from what I can see through the plug holes).

I've not had the time or funds to yank the head. Right now I'm thinking a stuck or burned set of valves. Maybe at worst case, some blown piston rings.

I've got another motor standing by at a friend's house if necessary, but I would much rather keep my motor in place. Lay any or all of your ideas on me......

 

[winterbeater]

You could try the old test of putting oil (IIRC 3 tablespoons) into the cylinders and rerun compression test. If numbers go up significantly, the rings are suspect. You can also pull the head, turn it upside down, fill combustion chamber with solvent and see what leaks out to check valves sealing? The number 1 plug should look pretty shitty at this point???

 

[RaccoonJoe]

#1 plug looks just the same as the others. some brown on the electrode, and some oily residue high on the threads that smells strongly of fuel.

Trying to ldo this without pulling the head off, due to time and money constraints. Due to the wonderful economy here in NE Indiana, my house is down to a single income.

 

[winterbeater]

Double check your compression on #1. If it is really 58lbs, there is nothing you can do with the head on. It's either head gasket, valves, rings, or cracked head or block. Whoops, could also be broken piston, but usually that tears up the spark plug too. Sorry about the single income. I know EXACTLY how you feel. Well, not quite, we are totally on unemployment.

 

[joe_peters]

Hook up a tach.

Pull all plugs wires loose, then let them rest on the plug tips.

Put on rubber gloves.

Start engine, then move the plug wires, one at a time, away from the plugs and note the RPM drop. If number 1 is that weak it should have little, if any, effect on the RPMs. Redneck cylinder short test.