pineapple_tree

I’ve tried my best not to make a post about this, but i’m running out of options on why this is happening.

What’s happening, is that if I lay on throttle hard in first and second gear, she’ll sputter and buck from about 1.8k-2.2k RPM’s. Then no sputter. After I get into 3rd, I can lay on the throttle all I want, and it won’t buck or sputter.

I’ve also figured out that it doesn’t do it right when I start up, only as it’s warming up. It does do it sometimes when it’s fully warmed up, but it always does it as i’m warming up.

This makes me think this could be fuel related. How? That remains to be seen.

So, let me first say what I’ve tested.

I just replaced my MAP and TPS sensors, and I tested each of them. The TPS sensor responds to rapid throttle movements, as well as maintains a flat curve all the way from idle to WOT. MAP sensor responds to different vacuum changes well, and the voltage at each “step” is within spec.

I also tested my IAT sensor and the ECT sensor (the one on the thermostat housing, not the ECT sender at the back of the head), and both showed the right resistance at the specified temperature (also verified by using a thermal camera)

I also tested my vacuum, and since I have no idea what my true idle speed is, but judging by the tach (it has problems with showing the wrong RPMs, and I have no idea why), and at about 900 RPM’s, it pulled about 22 inches of mercury. I couldn’t find anything on what the normal range of vacuum for the 2.5 is, but a general rule of thumb is that anything between 18-25 ish is good.

I also tested fuel pressure, which came out to about 34 PSI. 44 PSI if I unhook the vacuum line to the pressure regulator. A little high, but not that bad.

Now, I know I have a vacuum leak at the intake, and I thought it needed a new gasket, but it still leaked. No idea why it’s not sealing right. But i’ve known about this leak and it’s not a “major” one, and this issue hasn’t been present until 2 weeks ago.

I’ve also replaced the ignition coil, as it was out of spec for its resistance, and I changed out all plug wires, plugs, cap, and rotor.

There’s not much else that I can think of that would cause this. The only real things I can think of is that either an injector is sputtering sometimes under load, the distributor pickup (or camshaft sensor, whatever it’s called) isn’t detecting timing right and it’s throwing off timing and the injector pulse), or it’s something else I haven’t thought of.

I’m really sorry this was a long post, but I would love some help, because i’m getting tired of throwing my head around when I just woke up

exasemech

Don't know but....
1)you know you have a vacuum leak...fix it
2)But other than that if the tach problem ("it has problems with showing the wrong RPMs, and I have no idea why), " seems like it's an electrical issue rather than mechanical issue(needle is stuck) I would wonder about the distributor pickup/cam position sensor whatever you want to call it. There is a reason the tach is messing up.

doublechaz

+1 to figure out why the tach is confused. I vote for bad ground.

The good news is that it is not likely to be a burned valve or melted piston top caused by that intake leak as that wouldn't come and go with different RPMs.

pineapple_tree

Well, I did check the grounds in the engine bay. Multimeter said there was little to no resistance, but i’m not sure about where the ground for the instrument cluster is.

And speaking of that, what runs the tach? Is it off of the ignition coil, the distributor pickup, or the crank sensor? I’m thinking that whatever might be causing the tach to act up might be causing my stuttering problem.

I’ve also noticed that my tach “jumps” up around the range I sputter, and then it reads the correct RPM’s.

I probably should mention I have a sport cluster

agreen

The tach is an indication of an ignition issue. If I had to guess... CPS?

Very Red XJ

When was the last time you pulled the injectors, cleaned and tested them? After cleaning the muck out, spray carb or brake cleaner through them while holding them open with a 9volt battery (you should hear a click)

Testing restance in cleaned injectors

pineapple_tree

Well, if the tach is run off of the CPS, then why isn’t it doing it when it’s fully warmed up? I replaced the CPS when I put in a transmission, and I had some problems with the plugs on both the male and female ends, so I ended up wiring them both directly to each-other, and made sure they were covered with heat shrink so they don’t short out. I’ve had so many problems with that CPS that I got one from the dealer to make sure it lasts.

But, with that being said, i’ve heard that the ignition coil runs the tach, but either is sputtering because of spark issues or fuel issues.

And to the other guy, I haven’t cleaned my injectors by hand yet. I’ve had them out to replace them with 4 holes, but they ended up spraying fuel everywhere. Never tested them either. I’d also imagine that they have 290k on them, but since this thing has no history whatsoever, i’m stuck trying to test parts and sensors until something comes up wrong.

lawsoncl

Stumbling under heavy throttle in the lower gears make me suspect wiring, especially where it crosses from the head to the firewall and wiring near the exhaust if the mounts are shot. Because that's when you get the most movement of the engine. You replaced the MAP, so I'm assuming you inspected the line and made sure it's not split. Can you cause the problem holding the brake and revving in gear? With the unknown history, it wouldn't hurt to confirm the bellhousing bolts are tight. At 290k, it's probably well overdue for an O2 sensor too.

doublechaz

lawsoncl>Stumbling under heavy throttle in the lower gears make me suspect wiring, especially where it crosses from the head to the firewall and wiring near the exhaust if the mounts are shot.

I had an ignition cut out that acted like an accelerator pump failure on my Volare. Turned out to be wire flexing when load was initiated, just as you describe. If it had been a tach/crank sensor wire it would have made the needle jump around...

pineapple_tree

Well here’s a problem. There’s only 4 bolts holding the actual bell housing in…

I’m pretty sure I forgot to tighten the top ones…

But why would the bell-housing not being 100% tight on the engine? Because I replaced my transmission about 4 months ago. I also did replace the o2 sensor about 3 months ago. Made a world of difference in just how it responds to my movements and the different gear shifts. Plus i’m getting 18 MPG in the city

pineapple_tree

I also should note that I replaced my drivers side engine mount and the trans mount because both were completely gone, so all that’s left is the passenger side one. I wanted to replace the other mount but it was 20 outside and completely dark

Very Red XJ

18 mpg in the city is GREAT
The CPS is mounted to the bell housing. It is only accurate when correctly aligned with the flywheel. Missing or miss-torqued fasteners can affect his alignment. Louse fasteners may have come very louse

lawsoncl

Yup, the CPS is attached to the bellhousing. So if the bellhousing moves then the sensor gets misaligned and can't read the teeth on the flexplate/flywheel. Hopefully you have enough extensions and flex joints to get up there without having to lower the trans crossmember.

pineapple_tree

That makes pretty good sense.

However, I think it’s more electrically related.

I just started up my Jeep, and I had my lights on as well as the door open with the dome light on, and as soon as I tried to crank it, on the very first crank, everything turned off. No lights, no nothing. And then it came back on and I could start it. Happened twice in 30 minutes. And each time it happened, it started to stutter in 1st and 2nd. This makes me think something deeper is going on, like a short circuit somewhere.

psf4x4

It’s been said, but…

I would fox known issues i.e. vacuum leak, loose bell housing, before further troubleshooting.