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Old 04-04-2014, 06:57 AM   #1
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Warm weather woes!!!

Hey guys! I'm a newbie here so be gentle, lol!

I have a '94 YJ with the 2.5 and it runs great all winter long, as soon as the ambient temp gets above 75 or 80 degrees outside I'm running down the road pretty good but if I have to sit in a drive-thru or at a red light very long it keeps idling fine and will rev good but when I hit the gas to go it DIES, spits and sputters!!!....it's a wonder I havn't gotten t-boned!
Also, at these temps, when cruising down the highway sometimes it starts loosing power and running like crap but I have found that if I turn the key off and back on (a few times) it seems to "reset" maybe 2 out of 10 times and runs ok for a while....until I have to stop again or it realizes it's "hot" outside. The engine temp is normal. I have replaced the crank sensor...I am hoping for ideas before I start throwing money at every sensor or ecu. The only thing Im sure of is it's not in the firing because I hooked up a timing light while it was cutting up like this and it never missed a spark.
Any ideas???? PLEASE!!!

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Old 04-04-2014, 08:07 AM   #2
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First off, welcome.

Second, it sounds like a fueling issue is your problem. Possibly TPS, but I wouldn't expect ambient temp to really affect TPS operation.

Get a hold of a fuel pressure gage and see what you have for fuel pressure cold vs hot, or at least when you're having a problem.

Also, make sure you really don't have a temperature problem. Your thermostat might be opening late, or not enough. I dont' trust the temp gage on my dash. It regularly reads about 20 degrees hotter than it really is. If you can get another temp reading, you can rule that out.

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Old 04-04-2014, 08:09 AM   #3
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If it's not spark, then it's most likely fuel delivery. change the fuel filter recently? If not start with that.
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Old 04-04-2014, 10:58 AM   #4
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Thanks a lot guys! I have recently changed the fuel filter and I do have a fuel pressure gage but let me ask this...if the pressure on the rail is low or erratic during the time its running bad how will I know if it is the pump or a sensor or ecu signal to the pump? I will change out the thermostat and coolant temp sensor today...
Thanks for the info and please let me know if anything else comes to mind!
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Old 04-04-2014, 11:09 AM   #5
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I don't think temperature plays into the fueling after the engine reaches operating temperature. My understanding is that it runs off the O2 sensor.

If you find fuel pressure problems, that should narrow it down to regulator or pump. If you don't find a pressure issue, then it's likely an injection issue.
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Old 04-04-2014, 03:01 PM   #6
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Okay I just got off work and barely made it home!

To rule out engine overheating I removed the thermostat (which did seem stuck) then I got it up to temp and when i sit idling a few minutes sure enough it wouldn't go! Strange how it revs really good good but soon as you ease out the clutch it DIES!

Fuel pressure at idle was a steady 28lbs, I got it "hot" where it would stall upon throttle and it would sputter and the pressure dropped around 15lbs....the thing is, if it dies or/and I recrank it it seems to "reset" and take a few minutes to run crappy again????? Whatcha think....ecu????
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Old 04-04-2014, 09:19 PM   #7
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Well, narrowed down to fuel so that's good. Start with the fuel pump relay, it's easiest to get to. I think the relay is the same as most of the other system relays, so borrow one of them (like wipers?) and see what happens. I doubt the ECU is bad. Your pump relay should get signaled right off the ignition switch.

If not a bad relay, maybe the fuel pump ground connection. Check the connection from battery to frame. To check the ground on the fuel sending unit, you'll need to drop the tank. The ground is soldered right to the plate on the sending unit and is prone to rusting out, especially after 20 years. If it is, you can splice it to a terminal ring and use one of the flange screws to get a ground.

If all else fails, then probably the fuel pump. If you get to that point, make sure you can get a replacement gasket ahead of time. I just had to do this, and getting a new gasket was a PITA. Even a new sending unit assembly, which is what I needed, did not have a new gasket.
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Old 04-04-2014, 10:02 PM   #8
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So did you have good fuel pressure? Sounds like your pump won't put enough fuel through under load.
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Old 04-05-2014, 10:22 AM   #9
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Ok....so today for giggles I reset the ecm and tested for codes before cranking. Here is what I got
33 - something about air condition circuit and I dont have AC.
13 - MAT sensor
23 - MAP sensor

Question....Should I replace these sensors or suspect a bad common connection like a harness...also I want to mention that anytime I hit a little water something gets wdt underhood and it runs like crap until it dries...maybe the two are related??

All the ground wires look good.
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Old 04-05-2014, 11:23 AM   #10
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33 - Common. For some reason, they didn't tell the computer to ignore this if no AC is present. Happens to us all.

13 - Check the vacuum lines first. Make sure it's getting vacuum. If Vacuum is fine then I'd replace the sensor.

23 - is usually IAC. Did you mean IAC or the MAP?


I have a 94 FSM and I can give ya the testing procedures for all the sensors so you're not shooting blind.
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Old 04-06-2014, 01:00 PM   #11
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Update.....I replaced the MAP sensor and the MAT sensor...codes are clear but after getting some heat in the engine compartment its still stalling and sputtering on acceleration and cruising..some backfire as well...also, flipping the ignition back while coasting does seem to temporarily reset and improve....ecu or ignition switch...distributor componebts?? Surely someone has had this happen! Craked head? Im lost and runnin out of money and parts!!!
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Old 04-06-2014, 07:00 PM   #12
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Drove a friends yj that used to buck. Like it wasn't getting fuel. Idled great. Just sucked when driving. Turned out to be the ignition coil. He had a mat and tps code that it threw. But went away as soon as he swapped the coil.
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Old 04-06-2014, 07:28 PM   #13
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Hey thanks Jeeprich25...I'm gonna kep this Jeep from now on so it won' bother me to have ALL new parts on it so I will put the coil on my list!!! A coil and TPS are the next things on my list...I'll let you folks know tomorrow if there is any difference.
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Old 04-08-2014, 10:38 AM   #14
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I mentioned in an earlier post that the fuel pressure was 28@ idle and dropped to 15 giving it throttle...well, after a little studying I find that the rail fuel pressure should increase under throttle as the fuel regulator closes off the return flow...Soooo....I'm going to put on a new fuel pressure regulator today because its a helluva lot easier to change than the fuel pump....which will be next if this doesnt fix it and checking for kinked or clogged lines...makes sense doesn't it?
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Old 04-08-2014, 11:32 AM   #15
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I was going to bring that up. There should be a vacuum line from the pressure regulator to manifold. See if you get a change in fuel pressure if you unplug it at idle.

The fuel injection on these is relatively low (we have hose clamps on our fuel filters!). The pump likely cannot keep up with higher flow, so it makes sense that the regulator reduces return flow under low vacuum.

I'm still a little perplexed by the apparent hot vs cold running change. Are you still seeing this difference? If you drive in the morning when it's cool out, the Jeep runs fine all the way? Then later in the day, when the temperature is up, it will run poorly again?
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Old 04-08-2014, 12:55 PM   #16
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You are correct....it was running great except afternoons when in80's and stopping in traffic too long....but now it dies at any time and pops and sputters, even in the cool mornings....if I back out the throttle it picks back up some..or when I flip the ignition. Im gonna put the thermostat back in because its running too cool.
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Old 04-08-2014, 01:39 PM   #17
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Quote:
Originally Posted by buckdaddy00 View Post
Im gonna put the thermostat back in because its running too cool.
The thermostat keeps coolant in the engine block until it hits 195 degrees, if you remove the thermostat, then coolant goes to radiator at all temps and takes WAY longer to heat up.

Edit - Gah I read that as not gonna put it in. Sorry
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Old 04-09-2014, 08:52 AM   #18
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I'm definately on the right track here! I changed out the pressure regulator and found that the return line is stopped up...probably at the metal lines near the rear axle...this non return has got to be a pump killer!!! So tank will be dropped this weekend for a new pump...still dont know what to do about the metal lines. I was hoping they sold a preformed replacement set but I havnt been able to find them...any ideas???
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Old 04-09-2014, 09:18 AM   #19
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Stopped up? It's physically plugged with something?

The fuel lines are just standard steel line. Feed should be 3/8, and I think return is 5/16. Line to tank is just a rubber hose with a clamp.

Be careful dropping the tank. If you can pump fuel out of it first, that is the best thing to do. Disconnect you fuel filler and breather hoses next. When it comes to the tank, drop it down slowly. I like to put cinder blocks under mine on both sides, and grab it with a jack in the middle. I also built myself a trans adaptor plate for my jack that works well for fuel tanks. Drop the tank down first just enough so you can reach in and disconnect the fuel lines and electrical.
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Old 04-09-2014, 09:36 AM   #20
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Is your tank a 20 gallon or a 15 gallon? If the tank is limited to 15, but physcially a 20 gallon tnak, this would be a good time to do the tank mod and get use of the extra 5 gallons of space.
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Old 04-09-2014, 12:16 PM   #21
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Yeah, I have the 15 gallon tank...not looking forward to pulling it but it looks easier than a couple I've done, there seems to be a little more space under there. May check into the 20 gallon mod.

9T4YJ, can these steel lines be cleaned out are should they be replaced?
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Old 04-09-2014, 12:31 PM   #22
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Depends on why it's blocked. IF the line is rusting, you'll just have the problem again, or the line will rupture next on the feed line.

The return line doesn't really carry any pressure, it just gives excess fuel a route back to the tank. But have you confirmed there's actually a blockage? The line will probably go dry with engine off.

I guess at this point though there isn't anything more the check. If you replace the pump however, I recommend changing the pickup sock as well.
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Old 04-09-2014, 01:42 PM   #23
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Ok, from what I understand I should be able to blow through the return line without restriction...correct? I seperated it at the first disconnet and it was clear to that point so I put 120 lbs of pressure hoping to clear the line all the way through to the tank but it was definately a dead stop...I figure if high pressure air can't get through low pressure liqiud doesn't have a chance....so would everyone agree this should be a clear line?
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Old 04-14-2014, 07:37 AM   #24
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****UPDATE***
YES…..you should be able to blow through the pressure regulator return hose!!!!
I pulled the tank this weekend, it was quite a task, the service manual failed to mention that the exhaust would be in the way of the tank removal and of course the tank straps were rusted at the threaded parts so they both broke and luckily Advance were able to have me a new set the next morning.
The hoses from the tank run through a small space between the body and the cross member, this area is too small unless you have a body lift!!! As suspected the fuel return line was flattened at this location…obviously this was creating over pressurization of the pump eventually doing it in.
I replaced the fuel lines and I needed a new gasket but no one in town could even get me one except for the dealership and that would be a couple weeks out so I bought some cork material and made my own gasket and I doubled up since the rubber gasket was thick and spaced the assembly unit much higher than the cork, I also cut some of the bottom of the return tube to insure it wouldn’t bottom out. And, one thing I did was clamp an eyelet on a small wirer and bolted it to the assembly with one of the mounting screws so if the solder on the tank ground ever comes loose I will have a wire in place ready to go.
The fuel pump was the problem all along, I’ve had this Jeep 8 years and it has never ran this good. I actually enjoy driving my Jeep again and have plenty of power for fifth gear …that is, if I still had fifth gear (that’s the next project!)
Thanks guys!!!
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Old 04-14-2014, 11:26 AM   #25
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Woot nice Glad you got it up and going correctly

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Old 04-14-2014, 12:11 PM   #26
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WOW! talk about needle in a haystack!!! Thank you for the update a lotta times you never hear how it turns out!

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