Help someone I am over my head!!!!!?

Question

I own a 1991 Caprice with a 5.0 engine the car starts quick and idols smooth even in sub 0 weather however, after the engine reaches full op. temp. and I start off from a dead stop or accelerate up hill the engine cuts in and out sharply.So far I have tried to fix the problem by replacing the T.P.S. sensor, the M.A.P. sensor, the distributor, the ignition module, the coil, the rotor, the cap, I have even replaced the main engine computer. I also replaced all wiring harnesses.also the fuel filter, and the fuel pump,and yet the problem persists! I cleaned the C.V.C. valve and checked and replaced all vacuum lines. This is driving me nuts and broke at the same time! There are no codes showing up on a scan. the cut off only seems to happen when the car is in closed loop. the car doesnt stall and runs fine at idle. The engine timing is set to factory specks the car only has 65,000 miles on is and uses no oil or overheats. any good ideas out there????????

I replaced the fuel pump just today and looked carefully inside the tank and it is clean as a whistle. the fuel tank had a crack in it a year ago and I bought a brand new fuel tank from the dealer for $1.000 bucks all fuel lines are clean .

The timing has been checked 14 times in the last month and it is at factory specks. the engine has verry low miles on it and does not smoke or burn oil. the compresion is at factory new levels

help!!!!!!!!

Answer 1

sell it

Answer 2

I own a shop, and work on such problems. You need to take a multi-meter, and check to see if you are getting NO LESS than 12 volts to the computer. There is a ground strap that runs from the engine to the body, is it missing or corroded? My thought is your computer is not getting enough fire or ground somehow. My second suggestion is; You need to have it put on a lap top computer, and go for a drive. The diagnostics has to be in snap shot mode, and as soon as the engine begins to fail, the computer will find, and take a picture of the parameters of everything that is going on. This equipment, not every shop has it because the software is expensive, and not used that much. The one thing you haven't looked at is; the temperature sensor could be bad, and the computer thinks it has never warmed up, too warm, or is otherwise not getting a logical reading from the sensor. I saw one do this with a bad wire that went from the sensor up the harness. Engine coolant had gotten into the harness, and the wire had to be replaced before the engine ever ran right again. This is NOT a mystery, and should be thought out well. If it runs fine up until it goes into closed loop, then it has to be something to do with the computer not getting the correct reading from the sensors that then come into play. Get a can of Electronic cleaner from a parts store, and clean every sensor connection on the vehicle if you have to, and pay attention to where the wires go into the connectors, as this is a good place for a wire to corrode, break, or come loose. Have you checked the EGR valve, is it sticking? These will do such a thing, and will cause the engine to run crappy. A clogged up IAC orffice in the throttle body may do this too. What does the exhaust pipe look like? Is it suited up even on the outside of the tail pipe around the opening? This would indicate the problem with leaking injectors. Did you check the injector harness with a noid light to see if it is dropping off fire? Is all the injectors clicking the same, as in one not clicking as loud? You can check this with a long piece of pipe to listen to them each. One may be bad, and only putting in little amounts of fuel. I will agree with dodge man, this may be one of those that has to be driven by the technician/mechanic in order to evaluate all the systems under driving conditions, as in the snap shot diagnostics done either with a lap top or good scan tool. A cheap scan tool like Auto Zone uses to diagnose problems with, will not do the job when it comes to getting real technical. Those people sell parts, and are not qualified to run testing that requires understanding the information they get out of the computer. Pulling information, and understanding the meaning of such information requires someone who is trained to do this. An example would be the sign wave of the injectors. This takes someone who knows a good wave from a bad wave. One last thing I can think of is; Check the engine with a vacuum gage to rule out a mechanical problem. I hope this somehow helps you.
Glad to help out, Good Luck!!!

Answer 3

It may not be in the engine at all, and you may be on a wild goose chase trying to pin it to the engine. It acts like the car can't exhale properly almost like the catalytic converter is starting to plug or there is some type of resistance or restriction in the exhaust system. Funny thing is cars will usually run OK when first started, but when they are warm or asked to do deep breathing they cut out. A plugged cat will not show up on the codes nor will an exhaust restriction. I had buddy that used to store his Corvette over the winter. Came time to break it out in the spring and it acted just like your car is acting. Bottom line.....he tore the engine apart went through the same agony you are and guess what? Mice had packed his mufflers full of dog food pellets. Check your exhaust!!!!!

Answer 4

Get a Haynes Repair Manual at the local Auto Zone or auto parts store in your area. It will troubleshoot and show you how to fix your vehicle. Also on the Auto Zone site has a section for vehicle maintenance

Click this and this is for the troubleshooting section. All check out the tech bulletins that came out on the vehicle.
http://www.autozone.com/servlet/UiBroker?UseCase=S001&UserAction=viewSimpleDiagInfo&Parameters=info

Did you know if the catylitic converter is plugged up, you can idle smooth but then on acceleration it may cut out. I presume you are saying that you can idle ok, but then when you start moving, the engine cuts off. Now if this is all the time then the converter is getting plugged up. But then if it works fine today then later acts up it is probably something else.

But even the great one like me would need the haynes and his trusty sidekick, the ohm meter and a couple of hours tracing wire routes. Seems a module is getting hot and then shorting out the engine. Buy the book and have fun.

Answer 5

After every thing that you have done to it i would think that it would be fixed. i can only think of 2 things that i did not read in the question (i think they were not there). 1.) you have made someone very mad at you and they put sugar in the tank. or 2.) You might have bought some gas that has water in it. Being as everything you have already done to it I would go to the parts house, and by some Heat put it in the gas tank, and let it idle for about a hour then drive it, and see if it persists.

Answer 6

It could be the catyletic converter. I had a car do that. However, if that is the problem be sure to replace the O2 sensor, a bad cat. can cause the O2 sensor to go bad (or the other way around).
Could be the EGR, but that should show up as a code.
Could be the coil.

Answer 7

Check the O2 sensor. It should throw a "Check Engine" light, but mine did not and I had a bad sputtering problem when the engine warmed up. Disconnected the sensor and the car ran fine. Ended up changing it.

Answer 8

Could be timing chain and gear needs replaced, possibly a valve job is needed. Have the compression checked. That will test the valves for leakage (if they check it the right way).

Answer 9

wow this is a real stump puller , try re-routing and insulating the fuel line in the engine compartment , if i remember correctly they get close to the block and exhaust at a couple of points , good luck .

Answer 10

hard one, i would check that the fuel line coming from the tank is picking up from the bottom, or tank may be very dirty and when going up hill dirt goes in line. give it a clean and see how you go

Answer 11

i own a repair shop ,and you,d think that with everything that's been done to it that it would have to run right ,but there are some of these that do give problems,i think yours is an electrical problem with it,but where to begin at,i wouldn't know to tell you ,since so much has been done and it hasn't improved it,id have to see and drive it to figure this one out,good luck i hope this helps.