hey guys thought i would try in here, havn't had any ideas in the 87-96 larger truck forum. Ive got a 96 2 wheel drive 5 speed, with the 4.9 motor. Here lately it has been running like crap, seems like it has a rev limitor. It especially does this when the a/c is on. Ive replaced the fuel filter, rotor, cap, plugs were last winter, i havnt gotten to the plug wires yet i know i need too. Ive run sea foam up the intake. Im starting to think that maybe the cats are plugged????? Not sure. Also i had to take the thermostat out as it was running a little warm not sure what thats all about, has a new radiator so i know its not clogged. Almost acts like cracked head but no water in oil or vice versa. so im asking you guys now thanks for any and all ideas!!!!

 

ha! the old 300/6! man i miss mine!

anyway, whats it doing to seem like its acting like crap?

about the thermostat, mine wouldnt stay cool with one in it. the rad was new-ish, the fan was fine, shroud was there. so i just took it out and no problems ever since.

 

I know from personal experiance that just because there is no oil water mix doesnt mean that the head isnt cracked. I had this happen to me, head cracked in the back 3 cylenders,

 

You might try down in the Big Bronco Forum, at least your powertrain has been in Bronco's.

But I can help on the cat possibility. Just diagnosed a plugged cat on one of my sons Buick V6 in the last month. A OBD-II scanner didn't come up with anything repeatable or meaningful. But the trusty old vacuum gauge did. Didn't have many vac ports to work with, disconnected the carbon canister purge line from the manifold, hooked vac gauge there, and temporarily plugged the canister purge solenoid hose end.

Started it up, at idle had about 18 inches of vac. Sped up RPM to about 2500 and held pedal steady, vac was lower, wasn't convinced that was the problem.
Had him put it in reverse with left foot on brake and bring revs back up to 2500 for about 5 seconds (loads engine), I think it was less than 10 inches of vac then. Looked promising, but using enough thin-wall vac tubing, I snaked the vac line out the back of the hood over into passenger window. Took it for a drive with me monitoring vacuum gauge. Just got going down a residential street, and vac dropped to 2 inches! I asked him how far down he had the gas pedal, he said barely down at all! OK, head it back home!

Had him unbolt the exhaust down-pipe to the cat inlet, and push the cat's inlet pipe off to the side so engine exhaust manifold could run wide open. Started it up (loud!) and put it into reverse, run back up to 2500 RPM while holding brake. With gas foot steady, had about 17 inches of vac. Good vacuum now. Problem solved - a plugged cat.

He was unable to unbolt the back of the cat assembly from the rest of the exhaust system, because it just torqued over on all of the rubber mounts. So we dropped the whole exhaust system onto the floor (no over-the-axle pipe on FWD ). Then with the cat unbolted, I tried to blow air through the cat using the top of my big shop vac (using the blower port on shop vac), with a wet rag to help the seal to it. Very little air came out, and I was having a hard time holding the vac hose on it, so much back pressure from that cat!

To check if any cat core pieces blew on into the muffler or resonator, we hooked the shop vac as a blower again, and blew it into the exhaust system right behind where the cat had been hooked up. Flowed well, so the rest of the exhaust system was OK.

I like troubleshooting things where you can get such a solid confirmation that you found the bad part! But I don't like working on cars or trucks in our terrible Texas heat this time of year

Anyway, out of this you can get some ideas to see if you have a restricted cat or not. The vac gauge test is cheap and easy, it cost us 0$. Driving it while monitoring vacuum is the quickest, as we found out.

 

Just seems like it has a rev limitor on it, especilly with the a/c on, when its up around operating temp i pretty much have to keep it floored in O/D to stay around 70, used to be able to accelerate pretty good in o/d. Thanks for the replys guys sure appreciate it.

 

I would definitely do a compression check. I miss my 300..... Map sensor, check for cat plugged. I recommend to everyone I meet: vac gauge and a good air/fuel ratio gauge. You can keep track and diagnose a lot of problems with those installed, and check your air intake temp sensor. That is what I would start off with.. I REALLY miss my 300....

 

hey guys thanks for the help, appreciate all the help. Figured out it was a clogged cat! Never occured to me till today to just go back and put my hand over the exhaust and low and behold there wasn't hardly crap coming out. Sooooooooooo right or wrong took my plasma cutter cut a door in them front one had nothing, back one had all the goodies, and cleaned out the guts. Folded the door down and welded it up. Left all the
o2 censors in place. truck runs like a freakin top now and a hell of a lot cooler. Again thanks for all the input!

 

Good! I couldn't use that simple test on the Buick, as flow seemed OK at idle and fast idle, but I really didn't know for sure what to expect, not having experience with that car.

If you removed ALL of your cats core, then I would not be surprised if the check engine light turns on eventually. The after-cat O2 sensor will see what the before-cat O2 sensor sees, no cleanup.

 

if it dont turn on after 40 miles, it wont.