fuel pump or cps problem

[weaselguys]

My 94 cherokee quit on me ,like it was running out of fuel.I got it home and now it wont start,fuel pressure seems ok but weak on volume when it is bleed off at the fuel rail.I decided to install a used pump I have after removing the old one and tried to check the both by plugging the in and turning the key on,but they made no noise.I checked the plug in and there is power coming out the middle plug,I teid hooking both my pumps to the battery and found they both come on when power is applied to the prong on one end.If they get there power from a prong on the end then why would my harness have it coming out the middle prong.Any ideas ?

[Mudderoy]

My 94 cherokee quit on me ,like it was running out of fuel.I got it home and now it wont start,fuel pressure seems ok but weak on volume when it is bleed off at the fuel rail.I decided to install a used pump I have after removing the old one and tried to check the both by plugging the in and turning the key on,but they made no noise.I checked the plug in and there is power coming out the middle plug,I teid hooking both my pumps to the battery and found they both come on when power is applied to the prong on one end.If they get there power from a prong on the end then why would my harness have it coming out the middle prong.Any ideas ?

Sorry I don't know, but please let us know what you find out when you do fix it. I'm sure someone else will jump in here and give you some ideas pretty soon.

How's the front end repair coming?

[weaselguys]

I think Im going to try a hot wire and toggle switch to power the pump,not the best fix but it should bypass any cps or possible computer problem.I will have most of my body parts tomorrow and it was supposed to go in to have the frame straightened this week I may have to put that off the radiator I bought for mine ended up having a leak and the place I bought mine off ebay wont ship a replacement until fedex picks up the old one on monday to return it.I was considering buying a 2 row from radiatorbarn instead I could have that by wednesday.I thought about the 2 row after reading about the problem you had with your elec fan rubbing on the 3 row radiator.Any way mine will be back on the road late this week to early next week,maybe not completely done but with improvments ,winch bumper,winch and new flairs if I can find some.

[BlueXJ]

Check the fuel pump relay. That is turned on with the key to keep the pump from running all the time. It runs then only when the pressure is required and the ECU tells it that.
Do you have spark. If not then check if you are getting power to each injector(noid lights) If either one is not getting power then you have a bad or failing CPS.

[weaselguys]

I have swapped out the relay with other ones with no luck ,I have had it started it ran for about 1-2 min and died,that should eliminate checking for spark,that leaves ecm,cps and volume from the fuel pump.What is curios is why I have power to the middle prong on the pump connection when they powerr up when power is applied to the end prong not the middle.

[weaselguys]

Replaced the fuel pump and have good volume at the rail,I had orange spark before but,no spark now,resistance test at the coil didnt look right,will test the cps and make sure there is power to the coil next.

[BlueXJ]

If CPS is bad then you will have no power to the injectors or the distributor. That pair are both controlled by the ECU but the CPS tells the ECU when it is OK to power them up. Check the injectors with "noid" lights and the power to the distributor with a multimeter. They both need a speed of 300 RPM which the starter privides and the CPS needs to see three seperate sets of signals before it tells the ECU to release power to the distributor and injectors.
Hope this short course in CPS' helped you understand their role in overall engine functions.

[weaselguys]

Replaced coil runs fine now.

[Mudderoy]

Replaced coil runs fine now.

Did it look damaged? Perhaps in your accident? I have a new one sitting at home in a box. I got it just on the outside chance that this was part of my mpg problem. Never changed it out.

[prerunner1982]

Did it look damaged? Perhaps in your accident? I have a new one sitting at home in a box. I got it just on the outside chance that this was part of my mpg problem. Never changed it out.

I was having an intermittent problem with my XJ (only happens when really warm outside, haven't solved it yet)... but thought perhaps the coil was the problem. It was not and I ended up keeping the coil in the XJ... A few months later my XJ died suddenly on my way to work. I started trying to diag... the usual... fuel and spark... I decided spark would be easiest to test and remember that I happened to have the coil. It is easy to get to and would rule it out if it wasn't. It fired right up. I realize this does not help the original post.... Mudderoy's post reminded me of it.

[pvt.Tadpol xj]

Hey Prerunner I have the same intermentent symptoms on my 1991 XJ and I have replaced all of the IGN.KIT.. well it runs better , but it still acts up now and then. I did find after I changed my POS. battery post and rearranged all of that wiring stuff there at the post it behave's a little better.And one more thing I have been applying the COMPONENT CONNECTION SOLUTION, or ANTI-OXIDATION SOLUTION to all of my plug-ins....:cool:

[4.3LXJ]

A coil can be fired and not look damaged. Many of them that are old school were filled with oil. Others are solid state. Heat is the enemy of all coils, since it increases resistance and builds up more internal heat. That is why some coils will fail in hot weather and work again when cool.

[prerunner1982]

A coil can be fired and not look damaged. Many of them that are old school were filled with oil. Others are solid state. Heat is the enemy of all coils, since it increases resistance and builds up more internal heat. That is why some coils will fail in hot weather and work again when cool.

Right... which was my thinking to begin with, but did not cure the intermittent problem.

[weaselguys]

My coil looked ok it even fired with a spark,it looked orange and to weak to me ,it did fail a resistence check listed in my manual so I replaced it and that was at least part of the problem,it was also the fuel pump the pressure was fine but I noticed that right before it died that the pressure would drop and then it would die,so I pulled the pump and the volume was weak compared to a used one I had so I swapped them.No pressure problem now its not dying anymore.But I must not have gotten the "o" ring in right becuse it leaks,so I get to pull the pump again.

[4.3LXJ]

You should use a new O ring when you take out your sending unit. It will keep it from leaking.