'90 ZR-1 Intermittent Power problems

[DarkAngel]

Hi everyone,

I need your help because i encounter a pbl with my '90 Z

The car start and run well until a certain moment when she start to have some power issue : she will stutter and stumble intermittently and when at idle she seems to vibrate and have some knock issue also

Recently i had to open the plenum and replace the Sensor Coolant Temperature
because the car didn't run at all (really hard to start, car was shaking, couldn't hold idle and impossible to drive)
I've also replaced the fuel pump with P240KC as suggested by Jerry's doc

Since i replace the coolant temperature, car runs well except the intermittent power issue


I've read on some other posts that it might be the injector resistance that fails on one or more injector

As the injector was already replaced when i got the car and i drove only around 15000 miles since the replacement, i'm surprised that it might be the injectors

Could it be something else like the spark plugs ?
In case, it's the injector, does the "magical" product that supposed to clean the injector could be any good ?


I've read the procedure to test the injector resistance but i didn't get exactly how to proceed as there is no pictures :(


Also if one is failing, do i need to replace them all ?

[1991 Corvette ZR-1]

Hi Darkangel,

It is best to replace the injectors as a set. From your description, it sounds like an injector issue as the car seems to run fine on cold startup but develops performance issues later. The knock at idle can result from a faulty injector(s) as well. Bypass the injector cleaner, that will not cure anything based on what you have described.

[XfireZ51]

Dark Angel,

Can u describe further the intermittent power issue you are experiencing?

[Matt B]

You probably know this already but this has seriously helped me to check my injectors http://www.zr1specialist.com/HAT%20Web/articles/Measuring%20Fuel%20Injector%20Resistance%20with%20 the%20Plenum%20in%20Place.pdf

[XfireZ51]

Here?s a helpful illustration of how to check injector resistance. Better to do after 30min heat soak.

[DarkAngel]

Dark Angel,

Can u describe further the intermittent power issue you are experiencing?

At stable speed, when the car is hot, sometimes she start to be twitchy and shaking a little when i push the gas pedal
but it's not all the time
and at WOT, i didn't notice any issue

Thanks for the illustration, that's what i was looking for as i didn't get exactly what i was supposed to do with the doc written by Marc Haibeck

Unfortunately as i'm not a member, i cannot open the pic :(

[Paul Workman]

Darkangle;

"The car start and run well until a certain moment when she start to have some power issue :"

Before diving in too deeply, I couldn't help but notice this symptom is very common to a primary fuel pump failure.
At startup, BOTH the primary and secondary pumps are activated for a few seconds before the secondary pump is turned off. The car starts, runs OK at first and then dies or runs rough: CLASSIC primary fuel pump failure symptom (and easy enough to check (& eliminate) before going further (IMO).


Fuel pressure?
Current reading?


Fuel pressure at idle should be ~45 psi ?

Current for both pumps = 8-10A @ the test port (red wire w/ black connector jutting out of the 1" wire loom by the windshield wiper motor.both pumps, ignition OFF)

[DarkAngel]

Darkangle;

"The car start and run well until a certain moment when she start to have some power issue :"

Before diving in too deeply, I couldn't help but notice this symptom is very common to a primary fuel pump failure.
At startup, BOTH the primary and secondary pumps are activated for a few seconds before the secondary pump is turned off. The car starts, runs OK at first and then dies or runs rough: CLASSIC primary fuel pump failure symptom (and easy enough to check (& eliminate) before going further (IMO).


Fuel pressure?
Current reading?


Fuel pressure at idle should be ~45 psi ?

Current for both pumps = 8-10A @ the test port (red wire w/ black connector jutting out of the 1" wire loom by the windshield wiper motor.both pumps, ignition OFF)

i will try to make that test but i've already changed both fuel pump few month ago so i doubt it could be this
when i've changed the fuel pump, fuel pressure was around 50 as i remember

[Paul Workman]

i will try to make that test but i've already changed both fuel pump few month ago so i doubt it could be this
when i've changed the fuel pump, fuel pressure was around 50 as i remember

You may well be correct. But! One of the biggest "gotchas" of troubleshooting is nested in the words: "It can't be the (whatchmucallit) because I recently changed them."

NEVER ASSUME! Always verify! Just so happens I installed two new fuel pumps (many moons ago now), and the problem I was having persisted. Can't be the fuel pumps, right? WRONG! The check valve on one of the new pumps was "kaput" right out of the box! I suggest you check it to be sure.

Statistics shows the most vulnerable time for a new device is (1) immediately upon putting a part into service, and (2) after the part has exceeded its typical MEAN TIME BEtWEEN FAILURE ("MTBF" is the common acronym).

[XfireZ51]

At stable speed, when the car is hot, sometimes she start to be twitchy and shaking a little when i push the gas pedal
but it's not all the time
and at WOT, i didn't notice any issue

Thanks for the illustration, that's what i was looking for as i didn't get exactly what i was supposed to do with the doc written by Marc Haibeck

Unfortunately as i'm not a member, i cannot open the pic :(

If u post ur email and/or pm me, I can send u the illustration directly.