Engine limited to 5000 rpm 1990 ZR1 LT5

[DPZR1]

Replaced parts:Fuel pump -From Jerry's
Fuel injectors - From FIC
Secondary fuel pump relay - From Chevrolet
1 butterfly port actuary valve - from Chevrolet
Both O2 sensors - from Chevrolet


Here's the problem:


Car pulls all the way to 7000 rpm in 1st and 2nd gear. In 3rd gear it pulls great to right around 5000 rpm and hits what feels like a rev limiter. The fuel pressure is at 42 gph at idle and climbs to 50 gph under acceleration, never drops. Upon hitting the rev limit, the vacuum gauge which runs at 20 hg drops instantly to zero and a code #54 (fuel pump voltage low) and code #61 (secondary port throttle system error) show up in the computer. When the problem happens the check engine light comes on and turns off upon idling. At this point the 5000 rev limit happens in every gear. If I let the car idle or turn it off for a minute, the problem resets it's self. Any ideas!!! Help!!!

[Kevin]

few questions:
who did the work?
how many miles?
Are you sure all the hoses are plugged in correctly?

[DPZR1]

All the work was done recently. A friend of mine is a 3rd generation mechanic and a genius. Literally!! We, mostly him did the work. The vacuum is holding through 1st and 2nd gear and it pulls all the way. Once you get into 3rd gear right around 5000 rpm the vacuum shuts down. Instantly!! To zero. We have tested the vacuum and it holds, plus it stays at 20 hg until that moment in 3rd gear. Because of this I believe the vacuum is good and the hoses are properly connected. Plus, we labelled everything before touching or disconnecting anything.

[DPZR1]

I wondered if it was something to do with an O2 sensor but wouldn't you get an O2 sensor code?

[DPZR1]

Everything I have been told is that their are two O2 sensors on the 1990 ZR1 LT5. Is this correct?

[tpepmeie]

I would surmise vacuum pump. in the low gears, there is probably enough vacuum in the reservoir to keep the SPT's open. by third gear, that's probably exhausted, so you would need the pump to provide the vacuum.

I've never had these problems, but just giving another idea.

[Pete]

Bingo,what Todd said (tpepmeie)

Ok it does not just drop vacuum the secondary MAP sensor (under ECM)
Has to see above 3.00 volts if it sees less the secondaries shut down and feels like you hit a rev limiter,sounds like your running out of vacuum.

Pete

Originally Posted by tpepmeie

I would surmise vacuum pump. in the low gears, there is probably enough vacuum in the reservoir to keep the SPT's open. by third gear, that's probably exhausted, so you would need the pump to provide the vacuum.

I've never had these problems, but just giving another idea.

[Paul Workman]

Nothing to add on the secondaries - The GURUs of LT5 have spoken!

As for dying after idling, that is not secondary port throttle (SPT) related. But, perhaps the most efficient way to get to that is to look at the plugs - easy enough to do, and if there's any doubt you can replace them cheaply with the AC Delco 41-602s (copper, no less) work very well, and for about $25 for 8 (much less than a tank of 93 octane) you can have a fresh set every season, if you are anal-retentive, or every 9k-11k miles (about 2-4 seasons for me). (Pete put me onto these plugs and they've been perfect in my "FBI 500+" package.)

OBD-I will not reveal plug issues when scanning the ECM, but they will look at the pair of O2 sensors. Are the cross points approximately equal for both sensors, or is one only a fraction of the other? (A lazy sensor can result in improper fueling commanded by the ECM, and also result in the spark plugs on the side of the failing O2 sensor to be sooty or even fouled (first-had experience)).

Q: Did you purchase new stainless injectors from FIC, or "rebuilt" injectors? (Actually, either new or "rebuilt" can have problems, but the reason I ask is because the failure rate of the "rebuilt" injectors - according to the # of posts on this and other forums - is noteworthy in comparison to new stainless steel injectors.) In either case, a static pressure test* is in order to be sure a leaky injector(s) is not the problem. (In one case, Bob G had a new injector that would not close and leaking to the point of hydro-locking a cylinder with fuel!)

but I would want to do a static fuel pressure test to make sure one or more is not leaking (which also would usually show signs of trouble (wet, sooty, etc) on the respective spark plug(s).

And, BTW, if there are any codes being thrown, the secondaries will be switched off by the ECM. So if there is a service engine soon (SES) light on, the secondaries will be shut off, or will not open in the first place.

*Static pressure test: With a fuel pressure gauge hooked to the Schrader valve (at the front of the passenger side fuel rail) the ignition switch is turned to ON, without starting the engine. The pressure should fall in the 44 psi ± 2# range and with the switch then turned OFF, the pressure should hold to within 1 pound for several minutes (mine held for almost 30 minutes when everything was fixed). IF there is a leak, you'll want to eliminate the fuel pumps' check valves by opening the fuel line under the fill cap and repeating the static test there. Otherwise, if the plenum happens to be removed, then check for the leak at the injectors first before going to the fuel lines at the pump coupling - would be my suggestion.

Paul.

[XfireZ51]

I'm w Todd. Solenoid/Canister.

[DPZR1]

Good thought and possibility! Thank you!