Failed secondary system? Where to start?

[Athens91ZR1]

Hello all,

I am new to this forum and am helping a family friend (original owner) get their 91 ZR-1 ready to sell. The car only has 24k original miles and is 100% stock.

Current Situation:

The car drives beautifully in the Normal engine mode but when turning the key to the Full engine mode, it falls flat on its face and it feels as though the ECU is more or less preventing the car from accelerating at all (too lean or too rich of an air/fuel mixture I am guessing). I am aware of the injector issues that the early years had due to ethanol content and the owners are saying that they had the injectors replaced about 10 years ago. But I am still skeptical about how good of a job the previous mechanic did installing them.

Where should I start to diagnose this issue? (I am mechanically inclined and have an E85 converted 3000GT VR-4 that people say is a hard car to work on so am not afraid to take off the plenum if need be and/or take on a new challenge to fix this ZR-1 for its next rightful owner).

Thank you for all the help and tips, in advance! Oh and if anyone in Colorado is looking for a great condition ZR-1, then message me to come check out the car.

Jordan

[Z51JEFF]

First check to see if the vacuum pump for the secondary’s is working,with the car off turn the key on to power the pump,you will hear it run for a short cycle then go off,this will repeat. You can also unplug the vacuum pump line at the connector by the ALTERNATOR,it will run constant. What type of injectors were used for the replacement?

[dredgeguy]

What are the colors or the car? Suggest you post up with some pics in the for sale section as people are always looking and might be interested in it as is.
Good luck

[Paul Workman]

"Jeff" is spot-on.

And, a good place to start is Marc Haibeck's troubleshooting article(s) on his ZR1 Specialist web site. It is quite comprehensive.

That said, usually, secondary port throttle (SPT) operation failure is easy to run down. Most of the problems stem from age of the vacuum harness components. And, the good news is ALL of the stuff is available from Jerry's Gaskets.

And, then there's fuel pressure* to consider: 45 psi at light throttle to 53-55 psi at WOT. Check for normal [4-5 amperes each for 8-10 amperes total] current to the diagnostic connector (with the ignition switched OFF).

*NOTE: If the fuel filter (next to the frame rail behind the right front tire) is partially blocked, it may not affect normal driving (i.e., lo throttle %). Only when going to WOT does fuel pressure fall way below the 53-55 psi range.

Fuel pressure regulator affects pressure too, but unlikely considering the mileage being so low. Just "tuck" that away for now.

NEVER ASSUME! TRUST ME.... Just because something was replaced, that in and of itself is no proof of normalcy. I'm speaking from experience with regard to those injectors: you'll need to verify uniform resistance across them when at normal operating temperatures. (A reading of either 12Ω ± 1 or 14Ω ± 1 is normal. But, a reading beginning at 10Ω is indicative of impending doom. A reading of 8Ω or less assures failure is well on its way and the entire lot needs to be replaced.

We can get into more specifics if needed. But, first getting some of the preliminary fundamental stuff (AIR-FUEL-SPARK) evaluated will point in the direction for the in depth stuff.

[Athens91ZR1]

The car is Polo Green Metallic and I believe it is called saddle leather interior (kind of a beige). What do you guys feel is a fair listing price, based on the low mileage (24k miles)?

I should be able to post photos by next week.

[Ccmano]

Here you go... this will walk you though it.
http://www.zr1specialist.com/HAT%20W...%20Working.pdf

As noted could also be a bad secondary fuel pump.
H

[Athens91ZR1]

Thank you, H!

I will verify all the steps you and others have provided, starting this weekend. Since it is a 91, the Full Power lamp should still be showing up on the driver's information panel if it is working, correct?

I think I remember only seeing the green light lighting up near the valet key...

[Z51JEFF]

Originally Posted by Athens91ZR1

Thank you, H!

I will verify all the steps you and others have provided, starting this weekend. Since it is a 91, the Full Power lamp should still be showing up on the driver's information panel if it is working, correct?

I think I remember only seeing the green light lighting up near the valet key...

90 was the only year with the full power showing in the panel,91 only has the small green light by the switch.

[Athens91ZR1]

Are the spark plugs easy to check while I am in under the hood? Any tips from experts or special extensions/special tools needed?

[Ccmano]

The plugs are all relatively easy with various extensions except #8 (pass side at firewall). With the right combination of socket and extensions it’s not too bad. A magnetic spark plug socket with an intergral swivel and wobble extensions makes it easy without removing the blower cover. There is also a good write up here.
H

http://www.zr1.net/forum/showthread....ght=spark+plug