1990 Throttle hesistation

[XfireZ51]

Chuck,

Here's a real easy way of doing it.

[Schrade]

THanks there Dom...

But I'll tell ya'; it's @ the point where if I take the long way around, I might find something that's @ the root cause of this issue.

And then again, I might NOT ever find anything...

[XfireZ51]

I can't tell from the video but does the stumbling continue or only just after you move the throttle?

[Franke]

Chuck, Your secondary injectors shouldn't cause a hesitation just off idle but it won't hurt to check (ohm) them anyway.
After watching that video again it appears to me that the ECM may be fuel mixture hunting just off idle - not so much of a hesitation. Could it be the O2's or ???

[Schrade]

Originally Posted by XfireZ51

Sounds like a lean surge to me. What % TPS was that? Did this start after the secondary elimination?

Originally Posted by XfireZ51

I can't tell from the video but does the stumbling continue or only just after you move the throttle?

It hesitates coming off idle, and if I hold throttle at about 1.6%, it lopes.

Above 2.4% about, it's fine all the way up...

I'm not even planning ohming the 2' INJ's

[Schrade]

Originally Posted by XfireZ51

Sounds like a lean surge to me. What % TPS was that? Did this start after the secondary elimination?

Is a 'lean surge' possible here, with 2 adjacent cylinders @ .012 Ohms??? (no FP leakdown)

And it's just as before, except 0% idle is perfectly stable now.

[Schrade]

Franke, Dominic - I'm about 99% certain that my answer is in posts 37, 38, and 39, on page 4 of this thread.

I don't remember at the moment how I got this DM data - help?

And can I get this data in a lined DM graph?

[Schrade]

Some more testing here.

TPS baseline (motor off):

.53V; 0% TO in DM

Screwed in TB stop screw

.55V; still 0% TO

Screwed in to .57V; TO still @ 0%

.59V; still 0% TO

TPS bouncing from .59V - .61V; TO% bouncing from 0% - .4% THIS IS .06 - .08 INCREASE, BEFORE TO% SHOWS OPENING. NO MANIFESTATIONS OF A PROBLEM ARE APPARENT AT THIS POINT, WHEN RUNNING.

.61V steady; .4% TO steady

.61V - .63V TPS = .4% - 1.2% TO

.63V = 1.2% TO steady both ends

.63 - .64; 1.2 - 1.6% TO

.64V TPS = 1.6% TO; steady both ends. This is where the idle swing begins, usually about 100 RPM's.

.64V - .66V; still steady 1.6% TO

SLIGHT more turn gives .64V - .66V; TO% bouncing from 1.6% - 2.4%. This is where more pronounced idle swing starts - about 350 RPM's.

.66V steady; 2.4% TO steady.

.66V - .68V; 2.4 - 2.7% TO

.68V steady; 2.7% TO steady. She won't hold 2.7% TO while running.

.68V - .7V; 2.7% - 3.1% TO

.7V steady; 3.1% TO steady

.7 - .72V; 3.1 - 3.9% TO

And the throttle stop screw is pegged. Not to worry; another @ hand 1/4" longer...

[Tyler Townsley]

OK lets throw in a ringer. in a lt-5 the spark and fuel is controlled by the dis module until about 400 rpm where it is passed to the ecm. I once had a dis module that was fine until about 400 rpm then it fell apart. Took me 2 years to find out that they make a dis checker. As soon as I used it I could see it falling apart on a handheld scope and I replaced the dis module.

Tyler

[Franke]

Not sure if you changed out that TPS or not but it seems like it happens at the same tps position each time. Your thoughts?