New to the forum and I need you guys and gals to put on your thinking caps. The Jeep is a 97 TJ with 2.5L 4 banger with a 5 speed. Really hasn’t ever given me any trouble but she’s doing this cutting out at highway speed thing now. Did it one time last year on my way home from work. Did it again this year last month roughly the same distance from where I left and then again coming home from work again. Now it’s doing it everyday. The engine doesn’t stall altogether, just starts sputtering and loses all power, with an occasional backfire under the hood (presumably at the air filter). Scoured every forum I could find. Seems to not be uncommon and no one ever comes up with a complete fix (or replies to their post stating what it was). Feels very much like a fuel filter getting clogged and not letting enough fuel to the injector rail. Except there is no filter, just the sock on the bottom of the fuel pump that is supposed to be lifetime if I understand correctly. Yesterday I dropped the tank and replaced the fuel pump (Bosch unit). Pretty straight forward job although a second set of hands would make it easier. Took it for a drive and it was running strong and went quite a bit further than normal before crapping out. No codes, no check engine light. Read more and the number culprit if it’s getting fuel is crankshaft sensor. Got one of those from Napa (not a Mopar part I know..). Again, went further this time but crapped out again. Got to thinking maybe it was vapor lock after putting a locking gas cap on it. Put original cap on it and again went even further, but not far enough. Haha. It did finally throw one code but almost instantly corrected itself. It was a P0171 Upstream O2 sensor. I don’t think it’s bad I think it’s doing what it should be went fuel is cut/lowered to the rail. There isn’t a shrader valve on the rail (that I can find anyway) to check pressure but I think the pump is working correctly. Air filter is clean (aftermarket cold air intake). Wondering about the return line maybe having junk in it and not letting enough air/fuel exchange take place. Maybe carb icing? It ONLY happens at wide open (or pretty fast) highway speeds for extended periods of 15-20 miles. No issues in town. Also wondering if thermostat isn’t operating correctly and when I’m going that fast the coolant isn’t warm enough for the computer signal and maybe it’s doing something weird for a very short term correction. When it loses power I put it in neutral and slide off the side of the highway coasting down till about 40. Watching the tach it drops down to about 300 and never really stalls and about 10 seconds later it goes back up to about 800 rpm’s and I can put it in 4th and go on my way. After the first time it might do it once every 2-3 miles or over and over ever 4-5 miles or not at all. Also seems worse on very cold days. Thinking about putting some cardboard in front of the radiator, at least partially. 15 degrees out and a mechanical fan spinning 2600-3000 rpm’s into the back side has me thinking it’s over cooling. Thoughts?
TJ Losing Power at Highway Speed
- Thread starter Normy
- Start date
Here are a few thoughts on what to consider:
1. Fuel Delivery: While you've already replaced the fuel pump, the possibility of debris in the fuel lines or the return line affecting fuel flow still exists. It might be worth checking the lines for blockages or kinks. A clogged fuel sock (though you mentioned it should be lifetime) could also restrict fuel flow intermittently, especially under load.
2. Crankshaft Sensor: You mentioned changing this out, but it's possible that the sensor is either not functioning well (even if it's not a Mopar part) or that the wiring/connectors to it could be damaged. An intermittent connection might explain the sporadic nature of the issue.
3. Vapor Lock: Given your mention of possible vapor lock, especially on hot days, it could be worth checking the routing of your fuel lines. If the lines are too close to the engine or exhaust, that could lead to vaporization of the fuel under high heat conditions.
4. Thermostat/Engine Cooling: You could be on to something with the thermostat. If the engine runs too cool, it could throw off various sensor readings and impact timings. If it's not regulating temperature correctly, it may cause the engine to run rich/lean intermittently based on false temperature readings.
5. Electrical Issues: Consider the ignition system as well. Worn spark plugs, bad ignition coils or faulty wiring could lead to power loss under load. An intermittent electrical connection can cause these symptoms, particularly if it's a colder day.
6. Check the O2 Sensors: The P0171 code you mentioned could indicate a lean condition, which may explain some of the sputtering. If there's a vacuum leak or an issue with the upstream O2 sensor, it can affect performance significantly.
7. Radiator Block: Given your thoughts about cooling and the temperatures you're experiencing, partially blocking the radiator could indeed help stabilize engine temps. Just be cautious not to overheat the engine, especially during stop-and-go driving.
I'd highly consider using a diagnostic scanner to check real-time data from sensors when it seems to be cutting out. Tools like this are invaluable because they allow you to see real-time data and what the engine is doing when it's running poorly.
Watching/charting fuel pressure, O2 voltages, fuel trims, timing and vacuum answers lots of questions.
-Mac
-Mac
Thank you for the replies. I have scanned the system several times and while it will read any codes that might pop up, for whatever reason it doesn’t provide live data I like it does in my other cars. My nightmare is a mysterious damaged wire buried inside a loom somewhere. It’s only happened while cold out so haven’t experienced a hot weather vapor lock. All that said, he’s my update for you all today. So I stuffed a sheet cardboard in between the grill and radiator (condenser actually) covering about 3/4 of the area and took her for a test drive this afternoon. 45 miles and not a single hiccup. Temp gauge got up to about 195 and stayed there. I’m thinking the thermostat is either stuck open or it’s just a low temp thermostat installed by the previous owner and the wind at highway speeds in the bitter cold is s just sending the computer back into warmup mode. That’s about all I can think of. I did fill the gas tank last night so I suppose it could be a vapor lock/return line issue also (or completely) but I’m gonna drive it all week and see if it presents again as the fuel level gets low. I had read a forum post about a guy that was just having problems at 3/4 to 1/2 tank and below so that would make me think fuel lines. Hoping to maybe having it figured out though and have it be a simple thermostat replacement
Update: Drove her to work a few times this week (20 miles each way) and no issues what so ever. Still extremely cold out here in Oklahoma but temp gauge up where it should be with the cardboard over the radiator. Figuring it's a stuck open thermostat I picked one up and am planning on installing it this weekend. Well on the way home from work yesterday it did the same thing again. Had been running great, no stalling, no bucking. Idle has been slightly off a little for a while, fluxuating high, never low, so figured I have a slight vacuum leak somewhere. Cleaned up the throttle body and it went to a nice 800 RPM idle. I also blew out the line from the charcoal canister to the fuel tank. It was nice and clear and moved air just fine. At this point it seems to 100% have to do with fuel level. When it's full it runs perfect and when it gets to about 5/8 full the problems start, and progressively get worse as level continues to drop. I don't want to fill it again until I can drive it without issue at all levels. I replaced the fuel pump with a Bosch pump, utilizing the original housing. I'm wondering if maybe the lifetime sock maybe isn't lifetime after all and I'm going to need an entirely new pump housing (to get a new sock since I can't find the sock sold individually anywhere). Didn't really want to do that due to cost, since my fuel gauge works fine, and because the pump itself is obviously moving fuel was fine). I see some posts that say the pressure regulator on top of the tank also has a filter in it and I'm wondering if that needs to be replaced. I never really bought into the notion the the weight of the fuel in a full tank helps push fuel through but what do you all think? I can drop the tank pretty fast and swap it out but would rather not pull the whole pump out again if I don't need to. Has anyone had an issue like this where you're having problems at less than say 3/4 of a full tank? Has anyone changed the pressure regulator on top and had good results? The inside of my tank was very clean so I don't think the sock is clogged up but who knows. Still not getting any codes with this issue. One other thing I am looking at is the TPS as I've read it can cause a random stalling issue if not operating correctly. I plan to check the voltage on the TPS tomorrow when I get home from work (if I understand correctly it should be between 1-4 volts and not have any spikes or dead spots throughout the full range of the butterfly). I did drain the coolant and remove the thermostat (it was in fact a 195 degree unit so must have just been malfunctioning to not maintain the system there -or very close to there- regardless of outside temperature), and have the housing and head cleaned up ready to go back in but I forgot to grab a new gasket with it so I'll be stopping at the store tomorrow and am wondering if I should pick up the pressure regulator while I'm there. Also still getting no live data on two separate code readers aside from "fuel pressure ok". Thoughts.
This is the sock...
https://www.amazon.com/gp/aw/d/B000CGM5DM?tag=wranglerorg-20
I had issues on my 97 rebuilding my pump assembly. Plastic was very brittle. I ended up installing a Brute Power from Rock Auto. Almost the cheapest pump assembly I could find. It's been good for a year now...went from Oregon down the freeway and ran the Rubicon Trail and made it home. And lots of Forest Service roads in between.
-Mac
https://www.amazon.com/gp/aw/d/B000CGM5DM?tag=wranglerorg-20
I had issues on my 97 rebuilding my pump assembly. Plastic was very brittle. I ended up installing a Brute Power from Rock Auto. Almost the cheapest pump assembly I could find. It's been good for a year now...went from Oregon down the freeway and ran the Rubicon Trail and made it home. And lots of Forest Service roads in between.
-Mac
Thanks for your reply and for the link. I just found a sock link at my local store as well. Was your pump doing the same thing (or similar) as what mine is described as? I get a nice discount at our NAPA and am thinking that if I'm gonna drop the tank and change the sock, I might as well put an entirely new pump in so that I get the pressure regulator as well. I actually love tooling on cars and trucks but hate when my effort is in vain. Does the fuel level issue strike a chord with you?
Pressure regulator (and another filter) is a seperate component. Sits on top of the pump assembly.
I rebuilt my pump because my fuel pressure was in the 30s. Bosch pump from Brazil lasted two weeks. Put original pump back in. Then my wife folded my Jeep in half and that impact sheered the plastic in the pump assembly. Discovered this getting the engine up and running before transplanting everything to another frame and tub. The discarded remains of a fuel pump assembly were in the junkyard tub and I bodged together pieces to make something work for a 1600 mile off-road trip. Pressure still in the 30s. Replaced the pressure regulator again. Same issue. Said fuck it and ordered the almost cheapest pump off Rock Auto...Brute Power...48 psi rock solid almost no issues. Occasionally has had the fuel level float "disconnect" on really heavy impact or bouncing. More jostling gets it back. Done it twice in a year. Might not have the pump clocked correctly.
Oddly enough the Jeep drove fine through all of this. I'm trying to improve my fuel economy and generally refresh things to increase reliability. Often out of cell phone range.
-Mac
I rebuilt my pump because my fuel pressure was in the 30s. Bosch pump from Brazil lasted two weeks. Put original pump back in. Then my wife folded my Jeep in half and that impact sheered the plastic in the pump assembly. Discovered this getting the engine up and running before transplanting everything to another frame and tub. The discarded remains of a fuel pump assembly were in the junkyard tub and I bodged together pieces to make something work for a 1600 mile off-road trip. Pressure still in the 30s. Replaced the pressure regulator again. Same issue. Said fuck it and ordered the almost cheapest pump off Rock Auto...Brute Power...48 psi rock solid almost no issues. Occasionally has had the fuel level float "disconnect" on really heavy impact or bouncing. More jostling gets it back. Done it twice in a year. Might not have the pump clocked correctly.
Oddly enough the Jeep drove fine through all of this. I'm trying to improve my fuel economy and generally refresh things to increase reliability. Often out of cell phone range.
-Mac
Got some work done this morning. Tested my TPS and it was within spec. Next I got the new thermostat installed and the cooling system is working properly now (with no cardboard). I noticed the old thermostat didn't have a bleed hole in the top nor did the replacement I bought, so I drilled a small hole in it and oriented it in the up position. I've never gotten good heat in the jeep and I think I must have had a large air pocket in there because of the lack of a hole to bleed air through. Anyways now I have hot heat as it should. Was hoping running at proper temperature would solve my problem but it did not. I bit the bullet and bought a new fuel pump assembly at NAPA. Was thinking about buying just the sock and pressure regulator for the top but the price was almost the same as a new lifetime pump assembly that came with both of those items, plus a new tank seal, so it was a no brainer (and I have a new backup Bosch pump I can mix into the assembly in case of failure). Anyway it took exactly an hour to drop the tank and replace the pump and get it mounted back up and running (second time is a charm haha). The fuel level was still low (problem was only presenting at 3/4 tank or less) so I knew this was either going to fix the problem or quickly show otherwise. Low and behold we went on a 50 mile round trip trek (before it wouldn't go more than 7-8 miles without stalling out) without a single hiccup, so I am considering it fixed. Only issue I have is that after fueling it up when almost home, the fuel gauge is now off by a bout 1/8 of a tank low. Maybe someone has an idea on fixing that without getting the pump back out and bending the arm down a bit. Anyway, hope this post helps someone down the road. Lesson learned was that if fuel level affects fuel starvation, either the sock filter needs replacement or the filtered pressure regulator needs replacement, and best to just do a full pump assembly instead of rebuilding assemblies unless you know for sure it's just one or the other parts. Thank you guys for your advice.
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