ZR1 Full Power Issue

[402Z]

Hello everyone,

Just purchased a 1991 Zr1 with 41k miles on it last week. Absolutely loving the car so far and still cannot believe I own one. It sat for a while and it being 30 years old it does need a few things but the main concern here is full power mode.

In valet, it runs perfect no hesitations revs smooth up until about 5k of course which I know is normal since the secondaries aren't kicking on. Now when I put it into full power mode and put the hammer down, it sputters, hesitates and although it does rev to 7k it is not a smooth climb up there. The service engine soon light did pop up, but I tried to pull codes and nothing was there only "H" codes which I read are history codes that aren't present issues. I listened for the vacuum pump but I am honestly not too sure what it is supposed to sound like, I will try and attach a video or google drive link in here so you all can listen. I did unplug the vacuum line that goes from the secondary pump into the plenum I believe, but did not hear the pump running constantly with the ignition on? I put a picture of what vacuum line I am talking about

Is there anything that is relatively easy I can start with to diagnose the issue? Like replacing something small to see if that works? Let me know what you guys think the issue is would love to finally experience Full Power Mode in this beast. Thanks!

Here is the google drive link for the video of the secondary vacuum pump:
https://drive.google.com/drive/folders/1nOMWtGPxDzbV-Uwf4H1Rf4LzhuIErXrJ?usp=sharing

[402Z]

Okay, so I realized that my secondary port vacuum pump isn?t turning on when I have the ignition on. Anyone know where I can get a replacement one?

[Paul Workman]

Okay, so I realized that my secondary port vacuum pump isn?t turning on when I have the ignition on. Anyone know where I can get a replacement one?

I assume you checked to see if it has power to the connector and the connector itself is in good condition. If so, I'll give you mine or Ami's - IF either is still in the cars. (With a modification to the ECM "chip", you can run w/o the secondary apparatus entirely. "If dey don't exist, dey seldom break and don't cost much!")

[Young1]

See Solutions at top of technical postings. See website zr1specialist.com. Use the search feature. This site is a host of info. I sent you a private message. Text me. I can get you through it.

[dredgeguy]

Your in good hands with Steve! Welcome and keep us posted.

[Paul Workman]

Welp. Apparently, both (mine and Ami's) air pumps went to good homes. Sorry I couldn't pass one on to you.

P.

[402Z]

I assume you checked to see if it has power to the connector and the connector itself is in good condition. If so, I'll give you mine or Ami's - IF either is still in the cars. (With a modification to the ECM "chip", you can run w/o the secondary apparatus entirely. "If dey don't exist, dey seldom break and don't cost much!")

Yep! Just checked the connector today and it read 11.7 volts with the car on in accessory mode. Guessing the pump just went out.. ordered a new one and it should be here tomorrow. Hopefully that'll be the fix!

[Z51JEFF]

You can get a new OEM pump for about $125 shipped. I'll get some info in a few hours.

[Matt B]

Hi Jeff, do you have an update on the OEM pumps?

Sent from my SM-G991B using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[JT ZR-Won]

The '90 ZR I had before this one experienced something very similar to what you described with yours. I only had the sputtering and hesitation with the valet key on full power. It turned out I had slightly clogged secondary injectors. I replaced all of them and the car ran perfect. Good luck and keep us posted.

Jay

[Paul Workman]

FYI, this is the vacuum circuit for the secondaries (see FSM). This diagram is from a 90, and the "SWITCH, DIFFERENTIAL PRESSURE" is attached under the ECM bracket. But, the switch is located UNDER the plenum on 91-95s.

NOTE: Normally, the vacuum reserve canister is charged by plenum vacuum when the engine runs. The vacuum pump & reservoir supplies vacuum to hold the secondaries open when vacuum drops at WOT.

However, if one chooses to delete the secondary vacuum system all together (as many have - running with the secondary throttle plates fixed open or removed entirely) you need not worry about any of that secondary headache and run on FULL ENGINE POWER 100% of the time (except at idle only).

[jss06c6]

Bryan,

I had a client car that was a bear to troubleshoot with same issues. Fuel pumps and secondary vacuum system were fine. There are two secondary injector modules on the LT-5. They are not made anymore, so you'll have to see if you can locate one. Check your FSM for the locations in your car. Only real way to test is to put the replacement in your car and test response. If it still fails, swap it to the other one and retest. If you can confirm that the replacement came from a fully functional LT-5, that is ideal.

If one has failed, you will only run on 4 secondary injectors, not 8, making the engine shudder when in full power mode.

Best Regards,

Steve Schroder
Crossed Flags Performance, LLC

Sent from my SM-G950U using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[402Z]

Found out the car had original injectors. Replaced them with brand new Delphi ones and got a chip installed at SGC. Car runs great now. Thanks for your input everyone!