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Unread 02-25-2013, 03:01 PM   #1
jsipe007
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1994 YJ Wrangler 
 
Join Date: Oct 2011
Location: Reno, Nevada
Posts: 466
Help Please!

Hey guys so, I had a rather long weekend. Now, to add to my frustration, i think another part on the jeep needs replacement

So here goes. Last week about midweek, i noticed my alternator appeared to be going out. I went to start the jeep friday morning and it was totally dead. So, my roomate helped me jump my wrangler. Unfortunately I should have paid closer attention but didn't. He crossed the leads at his battery and by the time I realized it, it was too late. I put my side on my jeep and hopped in the cab. That was my mistake, I couldnt see anything he was doing. Last time I EVER assume someone knows how to jump a car again. I asked him if he knew and he said yes... oh well back to the story at hand.

So anyway, I fried fuses right and left. The two main 50A fuses went out, my stereo, my amps, etc. I replaced the two 50A fuses (I believe one was to the alternator and the other i am not 100 percent sure about). Had my buddy help me from now on rather than my roomate... LOL

We replaced the alternator and the battery. Viola! jeep started and Im getting 14.7V charging. I thought that was the end of it, but I have been noticing something odd. My jeep (1994 wrangler YJ with 4.0L) now seems to run rough until I give it gas when i first start it. Its almost as if the fuel injected 6 cylinder is going to die. Its always at about 500rpms when this happens. I give it a bit of gas and its all fine, idles perfectly.

Today before heading to work at 1:20PM, it took quite a lot of cranking and I even had to pump the gas to start my jeep. Im wondering if the fuel is draining back into my tank. What do you guys think? Im wondering if its the backpressure sensor. No check engine light on, but the check engine light did come on when I drove with the bad alternator and new battery (just to get back home). Swapped alternators and the light went away.

Thanks for the help!

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Unread 02-25-2013, 04:10 PM   #2
calvynandhobbs
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1994 YJ Wrangler 
 
Join Date: Nov 2009
Location: Ledyard, Connecticut
Posts: 281
Don't know if this happened to you or not, but I accidentally put the jumper cables on my F250 wrong because it was completely dark and I didn't have a flashlight with me. Yes, I was being stupid. Anyway, got it started and the next day had a hard time keeping it idling and everything acted really screwy. I ended up frying something in the main computer and cost myself a $800 part. Make sure all of your fuses are still good or if you missed one. You may have even burnt a wire somewhere.
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Unread 02-25-2013, 04:38 PM   #3
jsipe007
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1994 YJ Wrangler 
 
Join Date: Oct 2011
Location: Reno, Nevada
Posts: 466
Thanks for the response! I was worried I fried something as well, but she idles and runs great! Its just after she has been sitting for a while it takes some cranking. Im going to try what a friend suggested: Ill cycle the key on for a few seconds, turn it off, then turn it on again. If it starts right up then ill go ahead and replace the backpressure valve. In the yj, is the backpressure valve part of the filter? I know it is on a tj.

Thanks!
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Unread 02-25-2013, 05:32 PM   #4
calvynandhobbs
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1994 YJ Wrangler 
 
Join Date: Nov 2009
Location: Ledyard, Connecticut
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I'm new to being a YJ owner so i couldn't tell you. I just bought mine at the end of January and so far the only thing I've managed to do is back it into the garage. Hopefully I'll get some garage time in the next couple weeks to start going through it.
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Unread 02-25-2013, 06:19 PM   #5
Que89YJ
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1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
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You need to check the fuel pressure and do the bleed down. You should see 31 psi at idle/39 with the vacuum line to the pressure regulator disconnected and maintain pressure above 20 psi for at least 20 min. after shut down. The check valve is part of the fuel pump and you want to make sure that is your issue. Low idle is not usual a fuel issue but difficulty starting is. Try cycling the key a few times and then cranking it.
Always always always start by checkingyour fault codes:
http://www.jeepforum.com/forum/f12/h...codes-1257145/
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Unread 02-25-2013, 07:46 PM   #6
jsipe007
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1994 YJ Wrangler 
 
Join Date: Oct 2011
Location: Reno, Nevada
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Thanks for the response! Im only getting low rpms on start. After i give it some gas, it becomes normal. Im thinking its the fuel pressure regulator so ill try what you suggested! Checking the pressure at the rails was going to be my next step

Its currently throwing a code 12. Im guessing thats from removing the battery. That is the only code showing though

Thanks again!
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Unread 02-25-2013, 08:23 PM   #7
Que89YJ
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1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
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Good. You need to look up cleaning the iac. Your iac controls idle and it sounds like it is sticking and needs to be cleaned. There is a good writeup on it and the throttle body but im on my cell so I cant link it. If you can't find it pm me tomorrow.
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Unread 02-25-2013, 10:30 PM   #8
jsipe007
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1994 YJ Wrangler 
 
Join Date: Oct 2011
Location: Reno, Nevada
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I will look into the iac. I have also been thinking about running some injector cleaner through my rig just since i dont think it has ever been done before.

Que89yj, If the iac were sticking, wouldn't it in theory be more of a consistent problem? When I cycle the key a few times (2 or 3) to try and build fuel pressure, it seems like the jeep starts and idles like it should. I will keep testing to see since once or twice isnt nearly consistent enough in my book.
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Unread 02-26-2013, 05:55 AM   #9
Que89YJ
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1989 YJ Wrangler 
 
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Location: Detroit, Michigan
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I agree check the fuel pressure. Idle when it is started and running has little to do with pressure if there is adaquet pressur to run it after steeping into the gas. The pump when it is running puts out way more pressure then the jeep can use. The IAC is a real common problem with idle issues. The hole for the pindl and the plunger get coated and the hloe is so small it doesn't take very much to cause issues. Check the pressure and bleed down especially. There are many issues with the pump check valve. Who knows, you might have an issue with both and they are both common enough on our YJ. IMO I am thinking your idle issue is the IAC. Here is the link. It is easy enough to do:
http://www.jeepforum.com/forum/f12/q...-body-1262267/
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Unread 02-28-2013, 08:42 AM   #10
jsipe007
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1994 YJ Wrangler 
 
Join Date: Oct 2011
Location: Reno, Nevada
Posts: 466
Que89YJ... you are the man! Thanks! Last night I tore into my TB and gave it a really good clean with some TB cleaner. I didn't know if the IAC coulb be cleaned with TB cleaner (since it has a plactic sleeve) so i just cleaned the IAC carefully by hand. Now my IAC and TB are spotless and the jeep is idling/running 100 percent better

Now that I got that issue hopefully resolved.... im running into another

Does anyone know what is included in the 50A circuit "Alt PWR 2"? this 50A fuse just tripped yesterday. Odd because I had no problem with it for almost a week. When I got back to my car and tried to start it, I found the fuse to be blown.

Im looking for an electrical short, but I would like to know exactly what I have on that circuit. That circuit should be completely factory, I have not modified it. Im assuming it is the secondary charging circuit? So if I have a short say at my amplifier, sending power to the frame, then the fuse would blow. Is this a correct assumption?
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Unread 02-28-2013, 08:50 AM   #11
Que89YJ
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1989 YJ Wrangler 
 
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Location: Detroit, Michigan
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The 2 50's are in parallel to each other. Replace the fuse and see if it happens again. There have been some cheap fuses that do not meet the current spec, and worse yet they are rated too high for the spot on some of them and have caused "termal" issues. If the fuse blows again then you need to pull the PDC and check all the heavy wires on the PDC. The 50 amp fuses protect the PDC to prevent it from cooking if the battery lines short.

Does your check engine light come on and go off normal when you cycle the key? You need to keep an eye on it because reverse feeding is never good for the ECU.
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Unread 02-28-2013, 09:52 AM   #12
jsipe007
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1994 YJ Wrangler 
 
Join Date: Oct 2011
Location: Reno, Nevada
Posts: 466
Thanks! Thats what I thought as well. I replaced both fuses with the same make and style fuse. That way at least hopefully they are manufactured to somewhat the same spec. Are you talking about the PDC under the hood? Or the fuse block by the clutch? Im assuming you mean the PDC under the hood.

Everything else seems normal. The seat belt buzzer functions properly and the Check engine light Comes on when the key is turned on as it should. I was also able to retrieve the codes without issue.

I will keep an eye on those 50A fuses. Thanks for your help!
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Unread 02-28-2013, 09:55 AM   #13
Que89YJ
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1989 YJ Wrangler 
 
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Underhood. Glad to here the IAC worked for you.
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Unread 02-28-2013, 03:37 PM   #14
jsipe007
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1994 YJ Wrangler 
 
Join Date: Oct 2011
Location: Reno, Nevada
Posts: 466
That was a great suggestion to clean the IAC. I would have never thought that cleaning the IAC would have such a huge difference! I assumed a crankshaft positioning sensor was going out or worse!

Since those two 50A fuses were in parallel, in theory, shouldnt both trip at the same time? Im really hoping that fuse tripped due to manufacturing flaw. Can you think of an easy way to check for a short? I was just going to hook up my volt meter or a light/buzzer to the fuse location and attempt to find the culprit by wiggling wires
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Unread 02-28-2013, 05:16 PM   #15
Que89YJ
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1989 YJ Wrangler 
 
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Replace the fuse with a good brand name. If you need to troubleshoot a short only if the fuse blows I am betting it will not.
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