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Slow until it get to 3k RPM. Help.

T

Tweeternpi

NAXJA Forum User
Location
Carleton,Mi
Ok, this is for my Wifes's YJ. I put a 95 4.0L in it to replace the bad motor. It ran Great for a day. Than it started acting up.

Fuel pressure is 34psi at idle and goes up to 41psi reved up. New Cap,Rotor,wires and plugs. The problem was worse until today. Before it would not go over 2500 rpm and was slow to get there. If you had it floored it would pop and backfire. I replace the cam position sensor. Now It is slow to get to 3k, but after it get to 3K it hauls A$$!!!Goes to 5000 rpm with no problems.

any ideas?

Thanks for the help. This board has help me alot with my XJ and friends XJ's.
 
was having a similar problem with my TJ, and not sure if its the same thing or not. I would accelerate at a fairly normal to slow pace until I hit about 2800, then it was like a turbo kicked in. What I have done is seafoam, and 44K - fuel addative from behind the NAPA counter. The seafoam told me of the exhaust manifold crack AGAIN, but I have not had the power surge yet, and am recording my mileage to see if anything changes. The 44K is working quite well at something, but Im not sure what - good luck
 
Check your distributor indexing.
 
Stock set up. I have a feed line and a return line.With the Fuel pressure reg on the fuel rail. Take the vacuum line off and the fuel pressure goes to 41psi. At idle.
 
I don't know (see, I admitted it!), but specs for an XJ 95 4.0 would be 30/39. Is 34/41 correct for a YJ, or is the regulator getting a little funky on you? Or, it could just be your gauge is a little off.
 
The Gauge could be off. Drove it today. And running at 1800rpm or 55 mph down the road. It feels like the timing is changing. It will run good than feel like it is retarding than run good again. What would make the timing change at a steedy speed? It just felt like it was Searching.
 
tweeter - save yourself a headache, run a $6 can of sea foam - follow directions for "into intake", and check for smoke from the engine bay. If it smokes there, you have a cracked exhaust man. Replace, and notice no continued problems with power, and gas consumption - Just finished mine today, and its a big difference. good luck
 
Been living with this off and on for years. It's annoying. Last week I set the TPS to spec, filled up with Premium, Seafoamed the IAC bleed, and changed the plugs.

It's gone. Great.

Now I have an intermittent bog off idle, warm or cold, completely random. I love my XJ Renix.

I did consider the distributor timing index like old mans suggests - that maybe the cheap gasahol I normally use was pinging so much the knock sensor retarded the timing. I got to wondering why we don't advance the timing the old school way instead of buying hi altitude CPS's? Of course, buying better gas does the same thing to a larger degree.
 
Ok well after some work got it fixed!!! For Mine it turned out to be timing. The Distributor was messed up from the old owner. Put a new one in got out the timing light and got it running good. Thanks for all the help.
 
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