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Discussion Starter · #1 ·
Struggling with a problem for the past year or more.
5SFE will not rev over 4000rpm's
I've done all the obvious, fuel pump, filter, timing, sensors, even a new ecu.
Looking the searches seems like a lot of other cars, makes, models have the same problem.
Since the '91 does not have a diagnostic plug and I use the old sst method she does not throw a code.
Read that a temp sensor might be a problem but that was replaced and the cooling fans run when needed.
The car runs perfect, shifts, starts, no issues except the 4G rev.
Any insight??
 

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Is this a new problem? Gradual or instant? In gear or P/N?

Have you checked fuel pressure (banjo bolt on filter or at cold start hose). Does it idle smoothly (ie not missing a cylinder)?

Map sensor might be old and off kilter
EGR stuck open
Partial injector clog
Exhaust partially clogged

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Discussion Starter · #3 ·
The problem showed up all at once. Injectors are all good, did a pressure check on the exhaust and no restrictions. EGR was decarbonized and vacuum tested last year, all good. Did a fuel pressure check with the banjo and that was on spec. Idles smooth, no missing, good throttle response. Might be map sensor, I'll check into that. I'm in the process now of changing all vacuum lines thinking they might be so loose around the fittings/sensors/switches. It's like there is a switch or sensor that is sending bad news to the ecu which in turn is limiting rpm(s). Another dumb question. Why is the VSV positioned on the back of the block. Thinking of moving it up so it's a little more accessible. That switch just might be where the problem lies.
When I originally got the car one of the vacuum lines was off on that switch and the car ran good. Since it is a direct connection to the egr. The valve cover at the time was leaking and everything in the back of the engine was soaked and the vacuum line just swelled.
You gave me some more possibilities.
 

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Discussion Starter · #5 ·
:) Did that also, The old girl is running good and there really is no reason for me to put it over 4g right now.
Did find that there is a problem in the map ckt. Not getting voltage to the map sensor. I think I should be getting 5 volts with the key on and not running. Getting nothing and looking at the schematics I can't find where the input should be coming from. Also have to check out the vsv., it's a oily mess back there now and probably one of the hardest areas to get to while laying on my back. Sorta doing a process of elimination. Disconnecting the vacuum line from the vsv to the egr seems to improve the performance. The egr tests good, no vacuum leaks and no carbon buildup after a cleaning last year.

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Weather is cooling now so I will run it and probably have a winter project,
 
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