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Have gas and spark but will not fire???

N

nate438

NAXJA Forum User
Location
NE
I have a 1990 XJ with the 4.0. The engine only has 60,000 miles on it. I left on vactation for 1 week and when I came back and tried to start my jeep it would only crank over, never fired. This is my daily driver and has never done this before. Here is what I repaced to try to solve the issue and still no luck.

-cap and rotor
-spark plugs and wires
-map sensor
-crank position sensor
-fule filter after the tank

After all this still nothing. I have gas in every cylinder so I know my timing chane is still on the gears and the fuel pump is working and the line is not plugged. Also have spark on every cylinder but for the life of me I cannot get it to fire. I belive my timming is way off or something electrical is causing this. I finaly took it to the shop and they had no idea, (not going back there again) Any help on what to check for would be a life savor, thanks!
 
nate438 said:
I have a 1990 XJ with the 4.0. The engine only has 60,000 miles on it. I left on vactation for 1 week and when I came back and tried to start my jeep it would only crank over, never fired. This is my daily driver and has never done this before. Here is what I repaced to try to solve the issue and still no luck.

-cap and rotor
-spark plugs and wires
-map sensor
-crank position sensor
-fule filter after the tank

After all this still nothing. I have gas in every cylinder so I know my timing chane is still on the gears and the fuel pump is working and the line is not plugged. Also have spark on every cylinder but for the life of me I cannot get it to fire. I belive my timming is way off or something electrical is causing this. I finaly took it to the shop and they had no idea, (not going back there again) Any help on what to check for would be a life savor, thanks!
Click to expand...

EDIT: Nevermind I am an idiot I reread and you DO HAVE spark.
 
Last edited:
You say you have gas in every cylinder. How do you know?

If there is actual gas in the cylinders, then the engine is flooded. If the plugs get wet, they will not fire correctly. If there is actual gas in the cylinders, then you need to dry them out.

Pull the plugs. Hold the TPS in the wide open throttle position (this tells the computer to shut off the injectors). Crank the engine for about 30 seconds or so. It should crank easily with the plugs out.

Make sure the plugs are good and dry and reinsert them and hook up the wires. If there is any buildup on the plugs, replace them with the cheapest Champions you can buy. By the way, the cheap Champions tend to work as well or better than most of the high dollar plugs.

Now, with the TPS still in the WOT postion, have somebody crank the engine. Once it starts to fire and start, you can let loose of the TPS.
 
I have pulled the plugs after cranking on it various times and every one has plenty of gas on it. I have also turned the ignition to the "on" position let the injectors prime and then pressed on the schrader valve on the fule ralil and it sprys gas out. Which brings me back to the original quesion. If it sat for a week and then would not start, why would getting the gas out of the cylinders or new plugs make it start now? The plugs that I have even though they are coved with gas still spark fine.
 
every one has plenty of gas on it
Click to expand...

If they have gas on them, the engine is flooded and will not start normally. Plugs that have been gasoline soaked can be rough to get started. Follow the proceedure and give it a try. I've only been working on vehicles for 40+ years.

Since the plugs have been wet, get some starting fluid and flush them after you pull them, then let them dry well.

If you have compressed air, when you pull the plugs, blow air into the cylinders to work on drying them out as well.
 
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Trust me I'm in no position to duobt any skills here, I will pull them tomorrow and give it a try and let you know what happens, thanks for you help.
 
old_man said:
If they have gas on them, the engine is flooded and will not start normally. Plugs that have been gasoline soaked can be rough to get started. Follow the proceedure and give it a try. I've only been working on vehicles for 40+ years.

Since the plugs have been wet, get some starting fluid and flush them after you pull them, then let them dry well.

If you have compressed air, when you pull the plugs, blow air into the cylinders to work on drying them out as well.
Click to expand...


I'll 2nt that, and pull the plugs out to night and let it air out over night.

Put the plug back in in the morning!

Better yet keep the plugs in the house(after you have completely dried them) so they will be warm in the morning. might help them to fire!
 
Letting it sit right now and air out, another question I thought of. Would the throttle position sensor have any effect on not letting it start? I have replaced it before because it was rinning rough and that helped but wasn't sure if it would hamper it from starting at all?
 
nate438 said:
Letting it sit right now and air out, another question I thought of. Would the throttle position sensor have any effect on not letting it start? I have replaced it before because it was rinning rough and that helped but wasn't sure if it would hamper it from starting at all?
Click to expand...

when you installed a new tps, did you adjust it with a voltmeter to specs?
 
No I did not, but that was installed over a year ago and I have had no issues with it at all. Do you think it came back to haunt me? LOL
 
Ok here is what I did today.

1.pulled the plugged and cranked it for 30 sec, then let it site a long time while I did the rest
2.replaced a battery cable just to cover my basis
3.cleaned the ground on the engine block to make sure I had good solid contact
4.replaced the plugs whith the original good ones, not wet like the current plugs

Did all this and cranked on it and still nothing, acts the same, so here is what I did after that

1. replaced the ignition control module out of my bro's jeep (identical xj)
2. replaced my battery with his

Still nothing!

This has to be a sensor or something electrical, but I have replaced all most all the components that would normally cause this. Any more ideas, not sure where to go from here but am bound and determined to get it running.
 
You may have cylinder washout.
Have you run a compression test? There is an easy cure if so.
I had my 93 4.0 do that one cold morning,
all 6 cyl had a 0 reading on compression. It was running good the night before burning no oil.
After some research on cyl washout, i cured it in about 1/2 hr and had compression back to 150 pretty quick. It started right up.
I posted this cure awhile back on another thread. If you need that cure post back or email me, Mine also had spark and fuel.
 
The shop did a compression check and said it was a little low, but they did not give me any numbers. Yead shoot me the thread and I will read up. Pretty much williing to try anything at this point.
 
Cylinder Washout Cure;
Remove all 6 plugs
Fill a squirt gun with your reg motor oil.
Squirt a couple shots into each cyl.
Replace the plugs
Turn eng over a couple times
If you have a compression tester
Test compression at this point, If no tester,
Put wires back on plugs and try to start.
A good battery OR charger is a plus here.
If no start, Repeat the process with a couple more squirts per cyl, Replace plugs and try to start again. No start repeat process again.
A can of starting fluid is handy to wash oil from spark plugs.
I had to do that process 3 times to get mine started. Hope this works for your's.
Post the results when you get time. Wayne
 
How much oil should I have in each cylinder, trying to figure out how to mesure this. Let's say the lid on a wd40 bottle, that full in each cyl or is that to much? So I take it all the gas in the cyl causes this compression to go down because there is no more oil in the cyl, but why all of a sudden over night like yours did?
 
are you pumping the gas when you try to start it?with fuel injected engines you do not ever give it gas while cranking.to check if you are getting spark(cuz frankly guys,I don't think he is)have a friend ready to crank the engine when you say so.1.take a spark plug wire off the spark plug but leave the other end attached 2.take a small flathead screwdriver WITH A RUBBER HANDLE!!!! if you look inside the end of the wire you just removed there is a metal plug-in.hold your screwdriver 1/4 inch from that piece of metal and have your friend crank the engine for 5 seconds.if you do not see an arch of electricity between the screwdriver and spark plug boot then you have a bad coil or ignition module or wiring.if you do have an arch then you have other problems my friend,of which i do not care to type about all night:viking:
 
I never really measured 2 squirts from a squirt gun but a WD40 capfull might be a little too much. Don't want too much and lock the motor up.and I'm not sure what too much would be.
A machanic told me that I don't put enough RPM to keep the cyl walls coated, a Lot of things on these eng give no warning. One minute they're working fine and the next minute they're broke.
I suppose it's like the flat tire, It was fine yesterday when I parked it,
I would try maybe 1/2 cap if you have a means to get it in without too much spillage.
Good Luck, Let me know if it works for ya!
 
When you say you have spark just how much do you have? It should be blue, never yellow and jump at least one inch at the plugs.

Next did someone spud you? Pushing a potato up the tail pipe will keep it from starting and mice can also plug up the exhaust or air intake at the air cleaner.
 
Mythbusters tried spudding a tail pipe and I believe it was an older Caddilac.
What happened was the eng compression blew it right out.
Not saying it will everytime but is it a myth or fact. Has any out there ever tried it?
 
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