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Jess

Random no-start & misfire

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I just finished a 6800 mile round trip drive from California to Alaska. About 900 miles in I filled up my tank and when I went to start the truck it turned over but didn't start. I cranked it a second time and it started. My assumption was maybe I got some bad gas. This was an intermittent problem for the whole two and a half week trip. Some days it would start every time, others it wouldn't start several stops in a row. I basically just crank it over and over until it starts. Giving it gas wouldn't seem to help. I also have had it shut itself off twice while at idle. 

 

About 3500 miles into the trip or so it started misfiring. I should say I don't know for sure if it was an actual misfire but it was a loss of power and a noticeable vibration. Sometimes it'd be stumbling while accelerating and then it would clear out, kind of like if you where blowing on a straw with a clog in it and then it the blockage shot out, I'd get this boost of horsepower back and it'd run totally fine. It seems like it would trigger when I'd slow down to idle or get in traffic or something like that. This become more frequent toward the end of the trip. My last 900 or so miles home it was missing pretty much the whole time. My gas mileage dropped from around 20 to 17.

 

After I got to Vancouver I did check over the Ignition system, everything looked fine except the rotor, the top contact was bent, had a cut in it and had some carbon on it like it was sparking weird. I replaced it and towards the end of the trip I replaced the distributor cap. Neither fixed anything of course. I have a very small amount of left/right play on my rotor but it's not wobbling or anything so I think my distributor is ok? My spark plugs and wires only have 13000 miles on them. I had replaced my Ignition Coil recently as well (don't see it in my spreadsheet but it probably has less than 13k on it after this trip as well).

 

When I got home I started looking for posts with similar issues and one of the big things I read to check was the CPS. As far as I can tell mine was still from the factory (291k miles now) so I replaced it with a Echlin/Napa part. it seemed promising for about a day (it could be just an illusion but my truck feels much more responsive) but I noticed a few stumbles again and then it just started not starting again. The misfire seems to be happening less but the lack of starting is just as bad.

 

I did cruisers ground refresh tips awhile ago and upgraded my battery cables with a 4awg kit from ksuspension last year.

 

Sorry for the wall of text, I'm just not sure where to go from here.

 

Thanks,

Jess

 

 

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Have you checked for fuel pressure? That is what is sounds like to me. Your pump is starting to go and isn't giving the correct supply for your engine to run happily most of the time. The other thing I would look at is reading your current CPS. Pulling this from memory, but it should have 0.5 volts (or more) while cranking. Someone correct me if that value is wrong. Anyways, I know you said it is new, but there have been cases of new CPSs that were faulty out of the box. So double check it.

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1 hour ago, JustEmptyEveryPocket said:

Have you checked for fuel pressure? That is what is sounds like to me. Your pump is starting to go and isn't giving the correct supply for your engine to run happily most of the time. The other thing I would look at is reading your current CPS. Pulling this from memory, but it should have 0.5 volts (or more) while cranking. Someone correct me if that value is wrong. Anyways, I know you said it is new, but there have been cases of new CPSs that were faulty out of the box. So double check it.

 

Thanks for the response! I tested my fuel pressure yesterday, it was 32psi at idle, pulling the vacuum line off the regulator boosted it to 40.

 

I saw a guide for CPS testing, I'll check it out in the morning. 

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Was it running poorly when you tested fuel pressure? Those numbers are correct, but won't tell you much if you don't test while the problem is happening. Just a thought. My fuel pump would put out the proper numbers every time I tapped on it. Then soon after it would drop pressure and the truck would start running poorly. 

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5 hours ago, JustEmptyEveryPocket said:

Was it running poorly when you tested fuel pressure? Those numbers are correct, but won't tell you much if you don't test while the problem is happening. Just a thought. My fuel pump would put out the proper numbers every time I tapped on it. Then soon after it would drop pressure and the truck would start running poorly. 

That's a good point. It was running fine when I tested it. After I replaced that CPS it never started with the miss, it would really only happen after driving it for a bit. 

 

I tested the CPS this morning and it looks like it has around 0.2 volts going to it. I got a replacement and will install it tomorrow.

 

I was wondering though, I know shavings from the clutch could stick to the CPS and cause it to have a weak signal, is it possible for the flywheel to get dirty and do the same?  This was the most concurrent amount of driving I've done in this truck and it was a lot of dusty, bumpy gravel roads + rain + my dumb oil leak from valve cover.

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Yea, .2VAC isn't good for a CPS. Most here will recommend you get a NOS one. Currently I have a NAPA CPS in my truck and it is working fine. (knocks on some wood!:peep:) Make sure you do Cruiser's mod to it. Gives a better reading. Check it out HERE.

 

The relevant statement is "A little trick for increasing the output of your CPS is to drill out the upper mounting hole to 3/8″ from the stock 5/16″, or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts."

 

I live on gravel roads and haven't had any problems with dust, oil, and the resulting slurry. Don't get me wrong, my engine is coated, but the CPS has been fine so far. Since its wedged in the bellhousing it should be kept mostly clean and clear from outside items.

 

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So Sunday evening after doing a compression test (I haven't been able to find mine for ages so I borrowed one + the fuel pressure tester from a friend and figured I'd check that as I've been meaning to for ages) I couldn't get it to start AT ALL. Monday morning I tried hammering the CPS closer to the flywheel with a long dowel to see if maybe it had come loose or something. It started on the first turn after that. I was kind of amazed! I let it idle for awhile because the battery had gotten low after the compression testing and after about 10 minutes it killed itself. I tried the hammer trick again and nothing. That was when I tested the CPS.

 

Today I replaced that CPS with another Echlin/Napa part and it again, won't start. I haven't tried drilling out the hole yet in case this one is bad as well and I have to return it. My meter is metering around the same .2VAC but I have suspicions that my meter is junk so I'm going to borrow one tomorrow to test it. I guess I could clean/drill out my original one and see what that does, I never metered it - I pulled it out to clean it and found it crudely wrapped in electrical tape because it had touched the manifold and melted at some point.

 

I tried bypassing the fuel pump ballast resistor as I've seen videos of it causing a similar issue, still no start.

 

I went over my fuel pressure notes and I did test it with the key on/engine off and it came in at 28PSI. Apparently, it should be 31? Could 3 PSI actually be causing it to not start? I did try some starter fluid the other day and it wouldn't turn over so I'm guessing that it isn't fuel related. I checked my fuel pump ground and it's still clean. 

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I would guess CPS and your meter is reading correctly. There have been multiple posts of crap new sensors. 

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3 hours ago, cruiser54 said:

No plug wires?????

I actually had my fancy set of ThunderVolt ones break and thought that may have been part of the problem. I replaced them with the Belden part from Napa, they probably have 10 miles on them. 

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Long story short, I think it's the fuel pump relay. I tried swapping (what I believe to be) the fuel pump relay and the oxygen sensor heater relay (the two closest to the starter relay) and it turned right on. I did some process of elimination to verify that (at least) that relay isn't working. It will start and run every time now with those relays swapped so I'll go grab some new ones and see how we do :crossfingers:.

 

Thanks everyone for the help!

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ever done this?

 

CONNECTOR AND RELAY/RECEPTACLE REFRESHING

 

10-pin connector

I suggest unplugging EVERY electrical connection in the engine bay you can find, whether engine related or not, and spraying it out with a good electronics cleaner, visually inspecting the terminals making sure they haven’t retracted into the plastic holder, and then plugging it back together.

There’s a critical 10-pin connector for the front lighting system located in front of the air cleaner and behind the left headlight assembly. Don’t miss that one. Also be sure that the connectors to the ballast resistor mounted near the air cleaner housing are clean and tight.

ALL of the relays should be removed, the terminals wire-brushed until shiny, and the receptacles sprayed out with contact cleaner. Then plug them back in. I do this on every Renix Jeep I purchase or work on for someone else.Ballast Resistor

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I did many years ago but this has prompted me to do it again as it seems there's a few I missed.

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