Need help diagnosing a sluggish grand cherokee

[barrett045]

I need help figuring out and issue I'm having and I'll do my best to explain it. It's a 2001 grand cherokee 6 cyl. About 180000 miles. So if it has sat for a while like a couple of hours or more it won't start on the first try but always on the second which seems strange. Very rarely but time after time it has a rough idle at lights. Last but not least another issue is that when I'm going down the road it starts to loose power and pressing the gas almost seems like it looses it faster but if I take my foot off the gas and then push it again it seems to fix it. For some reason I want to look toward fuel pump replacement but my knowledge about diagnosing these is limited so any advice helps.
Thanks in advance!

[cwaage]

My gut feeling would be throttle position sensor or idle air controller. My '97 Grand Cherokee would do the same thing, and we replaced both - they're about $30 each, and pretty easy to change.

If you get a Haynes manual, it has the procedure for testing both. You'll need a multimeter to do the testing, but it's also pretty easy.

[JeepN4kc]

My gut feeling would be throttle position sensor or idle air controller. My '97 Grand Cherokee would do the same thing, and we replaced both - they're about $30 each, and pretty easy to change.

If you get a Haynes manual, it has the procedure for testing both. You'll need a multimeter to do the testing, but it's also pretty easy.

TPS was my first thought as well. Especially the part about driving down the road losing power/pressing/repressing the gas pedal and getting different results.

[cwaage]

One additional thought on the TPS and IAC - both of these are "supposed" to light the check engine light and give a code, but out of the three times I have had to replace them - and verified they had failed (all on different vehicles), no error codes or light.

[barrett045]

Update.... I installed a new tps and still had startup issues right away... Went a couple days without the power loss but it's back too. I've replaced aic within the past 6 months so I don't know where else to go? Any other ideas?

[cwaage]

Did you disconnect the battery after replacing the TPS? It's not a part of the instructions, but sometimes it gives the computer a "swift kick" and it reads the new sensor correctly.

Is it temperature related? Does it run better or worse on cold days vs. warm days?

[barrett045]

Yeah I had the battery disconnected when I installed it. I want to say that it runs better when it's warm but the problems definitely happen no matter what.

[mujeeper]

Did you check the fuel pump? Might be a good time to change the fuel filter & while you're at it you can check the pump by leaving the supply end in a bucket. Turn the ignition in the on position (not start) and you should get a bit of fuel. If not, it may be your issue. I'm no mechanic, just trying to offer some input.

[cwaage]

If you're going to check the fuel pump, you should just replace it and the filter - you have to drop the tank.

Another possibility is a bad fuel injector. It could either be putting out too much fuel or not enough. You might try running some fuel injector cleaner through - cheap enough to try. I've had good luck with the Lucas injector cleaner, but there's tons of them out there.

[FreemansXJ]

Not sure on the loss of power, but I do know the Cherokees have a check valve in the fuel rail that is supposed to keep it pressurized so it starts right away. As it ages, these valves become weak and allow the fuel to drain back to the tank and the fuel rail to lose pressure. This in turn means that when you crank it over the first time, it doesn't start right away because fuel is being sent back to the injectors. By the time you crank it the second time, the fuel is htere and the rail is pressurized, so it starts. An easy way to see if this is the case is to turn the key on without starting it. You should hear hte fuel pump click on. Turn the key back off and then back on to start it. My guess is it will fire right up. As far as fixing this, most people just deal with it as it isn't that big of a deal once you get used to "priming" it like above.

Hope that helps,

John

[JeepN4kc]

Not sure on the loss of power, but I do know the Cherokees have a check valve in the fuel rail that is supposed to keep it pressurized so it starts right away. As it ages, these valves become weak and allow the fuel to drain back to the tank and the fuel rail to lose pressure. This in turn means that when you crank it over the first time, it doesn't start right away because fuel is being sent back to the injectors. By the time you crank it the second time, the fuel is htere and the rail is pressurized, so it starts. An easy way to see if this is the case is to turn the key on without starting it. You should hear hte fuel pump click on. Turn the key back off and then back on to start it. My guess is it will fire right up. As far as fixing this, most people just deal with it as it isn't that big of a deal once you get used to "priming" it like above.

Hope that helps,

John

Yep - this is definitely a possibility with the start up issues. I'm near positive mine is bad as I can hear the fuel draining out of the rails when I shut it off and my start-ups are hit and miss. Honestly, I'm in such a habit of turning my ignition to the on position for a second or two before turning it over that I don't even notice the issue.