Engine limited to 5000 rpm 1990 ZR1 LT5 - ZR-1 Net Registry Forums

DPZR1 · 07-09-2014

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 · 07-09-2014

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

DPZR1 · 07-09-2014

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 · 07-09-2014

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

DPZR1 · 07-09-2014

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

tpepmeie · 07-09-2014

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.

DPZR1 · 07-09-2014

Good thought and possibility! Thank you!

DPZR1 · 07-09-2014

Talked with mechanic and I am going to check vacuum from the vacuum pump side tomorrow. He mentioned though that if the reserve was not catching up with demand that the vacuum would drop slowly, makes sense, and in this case the vacuum is dropping instantly.

Kevin · 07-09-2014

how often does your pump run?

DPZR1 · 07-09-2014

Will check in the morning and reply.

07-09-2014	#1
DPZR1 Join Date: Jul 2014 Location: California Posts: 11	Engine limited to 5000 rpm 1990 ZR1 LT5 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!!!

07-09-2014	#2
Kevin Join Date: Jun 2005 Location: pittsburgh Posts: 4,633	Re: Engine limited to 5000 rpm 1990 ZR1 LT5 few questions: who did the work? how many miles? Are you sure all the hoses are plugged in correctly? __________________ It's not the car, it's the people - Doug Johnson 90 r/r "KEYS ON" nick named "T.L.B"

07-09-2014	#3
DPZR1 Join Date: Jul 2014 Location: California Posts: 11	Re: Engine limited to 5000 rpm 1990 ZR1 LT5 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.

07-09-2014	#4
DPZR1 Join Date: Jul 2014 Location: California Posts: 11	Re: Engine limited to 5000 rpm 1990 ZR1 LT5 I wondered if it was something to do with an O2 sensor but wouldn't you get an O2 sensor code?

07-09-2014	#7
DPZR1 Join Date: Jul 2014 Location: California Posts: 11	Re: Engine limited to 5000 rpm 1990 ZR1 LT5 Good thought and possibility! Thank you!

07-09-2014	#6
tpepmeie Join Date: Aug 2005 Location: Fishers, IN Posts: 780	Re: Engine limited to 5000 rpm 1990 ZR1 LT5 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.