4.0 Stumbles a highway speeds

tonkyman · 06-07-2003, 10:20 PM

My girlfriend has a 1993 Grand with a 4.0 that is driving crazy. She lives 150 miles from me so we do a lot of driving back and forth. About a month ago her fuel pump went out so I replace it and the fuel filter (150,000 + miles). Since I had already done a full blown tune up, wires, plugs, belts, hoses, air filter, and a full fluid change, i assumed that we were set for many thousands of miles without a problem ---- wrong. Now the engine acts as though it is running out of gas almost anytime you are at mid throttle. If you are running at a level speed with the engine not working very hard (it happens at 45 to 50, 55 to 60, 65 to 70) it spits and sputters like it's going to die or as if it is running out of gas but if you mash the throttle on down it gets up and runs fine. If you stomp the throttle it jumps into passing gear and lays you back in the seat. The problem only happens whn you are running at an easy level speed. The only other thing that causes me grief is it's idle. This jeep has never idled well since she has owned it. Every now and then when you pull up to a stop light the idle drops to nothing and it tries to die. Then it comes up to normal idle and run fine. Sometimes, first thing in the morning, you can crank it up, put it in reverse, back out of the driveway, then put it in drive and it drops to nothing and dies. The hard part of all this is I have VERY limited time to work on it before she has to make the 150 mile trip home so it's been kinday hit and miss. Do any of you have any thoughs on tthe poblem?? Let me know.

Thanks bunch,
Tony

ATJ03 · 06-08-2003, 05:26 AM

Everything considered , it sounds like a vaccum leak . Make sure
the throttle body and all connections are tight .

tonkyman · 06-08-2003, 08:28 AM

At first I too thought it was a vaccum leak but I think (I could ne wrong) I checked everything that could leak vaccum and found nothing. Is there anything "hidden" that I may have missed?

Thanks,

Dembones · 06-08-2003, 10:52 AM

Check the exhaust gasket. There is only one gasket for both the intake and the exhaust. If it's broken in one place, it will screw both up. I have the same problem, and it does the same thing. Does it miss a little when it idles too? Really check that gasket, and the thottle body gasket. Good luck.

**balloo93** · 06-10-2003, 04:51 PM

Using a volt meter check the TPS to see if it's within spec. Other than that I'd check the vacuum lines to the MAP.

tonkyman · 06-10-2003, 09:27 PM

I will check it this weekend for vacuum leaks but I have ordered a bored out throttle body and a new gasket because my thoughts have been leaning to the TPS. The problem seems to be at the same spot on the throttle regardless of speed. I have been thinking that it might not be a bad idea to go ahead and change the oxygen sensor while I'm at it. I've even kicked the idea to change the fuel pressure regulator while I was at it (you know, the old shotgun approach). Any thoughts??

**balloo93** · 06-10-2003, 10:41 PM

By nature (and the fact that I have two project vehicles and a DD to maintain) I tend to check the parts before replacing them. The fuel press reg can be checked with a gauge from AutoZone. Hell, show up in the afternoon and have them check it for ya on the spot.

I believe the 93 TPS's are non-adjsutable, so it will either work or it won't. It probubly wouldn't hurt to replace it.

Does the bored TB you bought come with a TPS? I read somewhere that some don't.

tonkyman · 06-11-2003, 07:02 AM

They told me that the TB has all the sensors on it. It's coming from Jeepers Creepers.

I don't like replacing parts without checking them first either but she's only over her one and a half days every fourteen (every other weekend) and if I wait to check the parts when she gets here most part shops don't have what we need and they have to order it (a day or two delay). I hate to put a bad part back on so I order everything I think it could be and shotgun it. My '93 Sport have 238,000+ miles on it and it still runs like new. I do a lot of preventative maintenance and keep it serviced LONG before it needs. My girlfriend has only had her jeep for 8 months and we're still learning about it and getting it up to MY standard. I got a very good buy on it so I don't mind spending a little money on it plus I know a lot more about it when I'm finished.

I'm replacing the TB with a bored out version because she loves to go fast and she drives in heavy traffic at mid throttle most all the time and she needs to move in and out of traffic fast. Anything to make her happy

tonkyman · 06-15-2003, 09:23 PM

Hi guys,
I just wanted to give you an update on my girlfriend's "93 Grand. When she got here this weekend I started quizzing her on how the Jeep was running. In my mind I had thought that the stumbling and back firing was being caused by water in the gas so I bought her some treatment (5 bottles) to use over the next few tanks of gas. I told her to run it as close to empty as she could without running out, then add the treatment and fill it up with mid grade or better gas. Well, that was two weeks ago and she told me that it was running better and not backfiring anymore but it still idled rough and had a flat spot in the throttle. To make a very long story a wee bit shorter, the Jeep had more than one problem. The flat spot at mid throttle and the rough idle was being caused by a bad oxygen sensor and the stumbling and backfiring was being caused by water in the gas. I'm still going to install the bored out TB because she needs the extra power but I think everything is working a lot better now.

Thanks for all of your help!!