- Hi Scotty,
- ‘96 Jeep Grand Cherokee, 282,000 miles, 4.0L straight 6. When the engine gets to around 180ish degrees it will seem to fire on one cylinder, stall if I’m driving. As soon as the thermostat opens, 185*, the Jeep will run better than ever. If I let it idle up, without driving, to 185* again it will run perfect. Then I have about a 6 hour window wherein I can start and stop the engine without a problem, even if it cooled. It’s the first start that’s the problem. Everything is new, sensors, water pump, thermostat and the radiator is relatively new.
Thank you Scotty for all you do, been watching for years.
What are your fuel trims like? Your vacuum hoses may be dry rotting off due to age, if they're the original vacuum hoses.
Don’t know that answer Justin. May I add; it starts immediately, no pedal, and runs fine up until near temp (185), then it chokes, until thermostat opens. Thank you for the question, wish I had an answer. Gets about 18 mpg
Get a basic scan tool, they're available on Amazon. You gotta troubleshoot a little in order for us to help you. If your vacuum hoses are original, that's likely your problem.
They appear flexible but I will get new as they would have at least 170k miles wear.
What code might I look to see for scan code, if I may ask?
Just scroll down until you see fuel trims.
Neighbor has scan tool. I’m on it! Going too look for something unusual, Will get back to you Justin. Thank you for the advice
I’m getting a P1391, loss of cam or crank signal. Scanner not showing fuel trim. All vacuum lines are plastic with rubber boot ends, only a couple of those.
Try STFT and LTFT. I know there's live data for that.
Going too look into vacuum hoses and a scanner (finally). Time for church, back later. Thank you again
I ordered the Bluetooth scanner Scotty recommended. Will get to the bottom of this. Neither my neighbor or I understood your last request. Your above my head Justin. Many thanks for your information, I will learn what you meant and be happy to upvote you. I’m going with your suggestion btw and will come back to let you know how it goes
Justin!, my hats off too you, Thank you very much! I found a cracked 3” vacuum line, attached to the speed sensor. It’s plastic while the others are metal. I’m thinking of replacing that sensor hoping for better fuel economy and smoother response from engine. Any thoughts on that? Certainly welcome. What a headache you solved for me. Thank you again!
Replace the cracked vacuum hose, they're only like $1.00 or so per foot, go to an O'Reilly with the vacuum hose in question and have them match it up.
Neither my neighbor or I understood your last request.
Assuming you're talking about the fuel trims that @justin-shepherd asked about, those are probably the most basic items available in live data. Even a first-year (1996) OBD2 vehicle with limited data should provide that information.
Fuel trims are frequently labeled LTFT (Long Term Fuel Trim) and STFT (Short Term Fuel Trim) in the data. If you do an internet search on those terms you will find detailed information on them and what they're telling you.
Thank you Chuck. I just received the BlueDriver OBD II that Scotty endorses. It doesn’t give me any live data for ‘96 jeep. I can’t even find vacuum line replacement for this jeep, frustrating, even tried RockAuto. Any suggestions?
The lines are hard plastic, it’s the boots at ends that I’m concerned about
I wonder if the catalytic converter is worn out. It’s about 13 yrs old. Mileage has gone to Haiti lately too boot
The catalytic converter is good for the life of the vehicle, unless there's an engine-related problem.
Thank you Justin.
Ok, on the hunt for proper vacuum line replacement
Fuel trims are frequently labeled LTFT (Long Term Fuel Trim) and STFT (Short Term Fuel Trim) in the data. If you do an internet search on those terms you will find detailed information on them and what they're telling you.
See below:
https://trade.mechanic.com.au/news/understanding-short-term-and-long-term-fuel-trims1
.
https://carkiller.com/scottykilmer/postid/99880/
Thank you whatchamacallit for the reference. I will be reading it now. Was disappointed to find out today my new BlueDriver scanner doesn’t read live data for my ‘96 Jeep. It showed the LTFT AND STFT with no possibility to read.
Trying to find vacuum lines, having trouble. Concerned about boots at ends of lines.
Replacing the old hard plastic doesn’t concern me as much as the rubber boots. Perhaps I don’t need them? Any thoughts on this would be most appreciated. Thanks again
Excellent article! Thank you