Power problems with the XJ

Soo I got the 2nd hand stroker (1990) in my xj 88 manual. The power feels the same as it was before with the worn out 4.0, as you can prolly guess I'm not too happy, I think I got jipped. I fixed a cracked Vac line, replaced some grounds, it helped a little. But after I cleaned out the TB with some TB/carb cleaner I took the Xj for a spin and It lacked alot of power. The RPM's with go through the whole range, but it doesnt pull at all. Could I have messed up a sensor or somthing? Also the motor is out of an auto xj not a manual, could the wiring be messed up or somthing? I havnt check for fuel problems or anything, or the timing, I'm just trying to find out where to start.

Thanks.

I replaced the fuell filter today and i dont tell a difference. I need some real help here. Please.

How's the exhaust system? Maybe the cat's plugged and excessive backpressure is causing the loss? Have you checked the fuel pressure? Make sure the FI isn't starving.

I put a cat back on it a few years ago so thats fine, could be the cat. How do you check the fuel pressure?

Hollow out the cat and see if that helps. The other things I suggest are to do a compression test on all cylinders, check the intake manifold vacuum at idle, and check the fuel pressure (using the Schrader valve on the injector rail) with the vacuum to the fuel pressure regulator disconnected.
While you're pulling the plugs for the compression testing, check the color of the deposits. This can tell a lot about whether the engine's running rich, lean, burning oil, detonating, or running fine.

Since you replaced the engine, and it had no effect, I would look at things you did not replace which are????? Intake throtle body? Exhaust system? Look for a restriction in those.

Also, look for a lack of fuel pressure or fuel capacity / flow rate under load.

problems with Injectors, week ignition, worn TPS, O2 sensor, temperature sensor, combinations of all of these, and distributor timing.

Distributor basic timing could be off one tooth, that is a common problem in your current situation!!!!!!!!!

There are detailed threads on all of these in this forum already, search and read them for lots of ideas.

I have been working on an 87 XJ for 2 years that barely ran power wise when I got it, and I have found all these problems over the last 2 years and each fix has added to improving the power and MPGs.

Also check and clean all those ground wires on the firewall (2), engine block (2) and battery and recalibrate and test the TPS afterwards.

Well today I pulled off the valve cover an re indexed the timing, the motor must be cammed because i had to cut the ears on the distributor in order for it to line up. I pulled the plugs and realized that they were too "hot", they were 3926, factory is 3924, and I bought 3923, and some wires. Did all that and nothing has changed. Is it possible that I messed up a sensor on the TB when I sprayed it down? Because thats when it lost a lot of power. Tomorrow I'm gonna gut the cat, we'll see how that goes.

AD-8 said:

Well today I pulled off the valve cover an re indexed the timing, the motor must be cammed because i had to cut the ears on the distributor in order for it to line up. I pulled the plugs and realized that they were too "hot", they were 3926, factory is 3924, and I bought 3923, and some wires. Did all that and nothing has changed. Is it possible that I messed up a sensor on the TB when I sprayed it down? Because thats when it lost a lot of power. Tomorrow I'm gonna gut the cat, we'll see how that goes.

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Could the timing chain have jumped instead of it being a cammed?

Sounds like that stroker has a history?

You failed to mention that it had power before spraying it down, I guess you mean sprayed down water? Water is big no-no for Throttle Position Sensors, TPS. They are like Cats, they hate water! :laugh: Save the Cat, replace the TPS sensor if you hit it with water, or try the Oven bake process someone described here last week.

I gutted the cat today and wow, it made a huge difference, it drives like a different vehicle. I've got a TB off of a 88 that I'm gonna throw on there pretty soon, we'll see if that makes more of a diiference. Thanks everyone.

I still haven't pinned down the problem. Today I put a different throttle body on it and switched to another set of injectors. Nothing changed. It just really lacks low end power. I've got the idiot cluster so no tach, but I'd guess at around 2500-3000 RPM's It just takes off. Below 2500 it has no power. If you floor it from like 5mph its like your accelerating normally until it kicks in. I mean you can feel the power kick in all at once. What could the problem be? Does that mean its running rich? It backfires out the tailpipe, which I think means it's rich, but the plugs look fine. I don't understand how it could be rich, its a 4.6 with stock injectors. Do I need to advance/retard the timing?
Any help would be appreciated.

Does it have an EGR valve on it?

I do believe. The intake manifold that was on the motor before had the egr valve pinched off.

have you checked/adjusted voltage of the tps. on an 88, the tps needs to be within specs and is not like the HO engine were it does need to be adjusted.

also the tps for a manual and auto tranny is dfferent.

I havent adjusted the tps voltage, I dont know how. But i did just put the auto TB and TPS back on the motor. The auto TPS has 2 plug-ins, where the manual has 1, dont know if that makes a difference. What about the EGR valve tho?

For an 87-90 4.0:

Test is done with throttle closed, connectors connected, ignition on, engine off. Insert probes through back of connectors to make readings. Use a high impedance meter. Adjust TPS by loosening mounting screws and turning in mount.

For manual connect + probe to terminal A, and - to B. Take a reading, which should be in vicinity of 5 volts but probably lower. Note the reading well. Now move the positive probe to terminal C. The reading should be 16 percent of the previous reading.

For Automatic, use the square, 4-terminal plug. Connect probe + to terminal A, and - to D. Note reading, which should be in vicinity of 5 volts. Now move probe + to terminal B. This reading should be 82 % of the first.

My stock 87, 4.0, went from nearly no power, extreemly anemic, to about 65% of normal after installing a set of new, MATCH flow rate fuel injectors. I have about 18 used, junk yard pulled, fuel injectors that are probably good for water the lawn now. Got another 20% of the power back with a new muffler.


I got mine from www.fiveomotorsports.com

I got to thinking that if the FI flow rates were not closely matched (some injectors were worn more and were flowing better than others) then some cylinders were running rich and some lean since the computer can not see the individual injector A/F ratio results of each opening pulse signal, it more or less averages them out as it sees an average A/F mix in the exhaust pipe (I think? I don't think they can do the timing calculations needed to distinguish when a fired cylinders exhaust gases are passing the O2 sensor, it is too complex, too many variables.....). So you might end up with 3 running rich, 3 running lean and lossy power output as a result. If it had 6 O2 sensors and 6 exhaust pipes the computer could manage each fuel injector individually, but in realty these things are looking at a moving A/F ratio average, adjusting the next fuel injector based on the last reading from the O2 sensor.

Therefore, a few off injectors could severly affect power performance.

May not be your problem, but was a big part of the poor power problem with mine early on. It went from about 50 hp at WOT to about 120 HP at WOT with just new, certified and tested, "MATCH" (flow rate) fuel injectors from Five-O.

How many lbs would you suggest for a 4.6 stroker?