Searching problem

Merk

Merk

Donating Member
this one has me baffled:

not sure how to explain it, but the truck (at idle and cruising) searches, almost like it doesnt know where to idle.

Looked into the manuals, which pointed me in the direction of a bad O2 or bad MAP. Replaced both and still the same.

Vaccuum is 28 inches at idle, and fluctuates between 2 and 3 inches when searching.

My recent change to the truck was the injectors (stock replacements), where I found a broken (cracked) nipple on one of the old injectors.

Hopefully, this symptom has happened to someone and can shed some light.

Merk

Edit: here is an AVI of the tach while searching
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Hot box vaporizer
 
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ed hess

ed hess

race or get outta the way
cant tell you whats wrong but i usually see only 18-10 vac on my guage!

your seeing 28?

whats up with that!

ed
 
ed hess

ed hess

race or get outta the way
yeah merk look like you really suck! er rather your truck does...

sorry i couldnt resist :D

ed
 
92Ty#1524

92Ty#1524

New member
Where are you reading Vac at? 28" seems a bit much.

Datamaster could be useful. I'd be curious to see what your IAC is doing.
 
T

TyMeUp

New member
'Surging' is usually an A/F mixture 'lean' problem. What are your BLM numbers at idle and at 3000 RPM? Greater than 128 = ECM adding fuel to correct for lean condition.

The following is sometimes called an "open loop diagnostic procedure". It eliminates the ECM's control and correction of the basic engine operation.

1) Disconnect, count to 10, and reconnect the battery to clear all fuel correction BLM.

2) Disconnect the O2 sensor to keep the system in open loop.

3) To eliminate the MAP, disconnect it electrically. The ECM will now base fuel control on TPS (default mode) and eliminates the problem of changing vacuum causing A/F mixture changes.

4) Disconnect the IAC (after starting) to eliminate ECM control of idle RPM.

Now you can use a propane torch (no, don't light it) to verify a lean condition. Open the torch valve with the tip pointed at the air intake. RPM increase = engine lean.

You can also use the propane to locate vacuum leaks. In general, a vacuum leak will not cause a big leanout on a Speed-Density engine control system. The MAP sensor 'sees' the leak the same as more air coming through the throttle - less vacuum. However, a vac leak in one intake runner will affect that cylinder (make it weaker than the rest) and cause a rough idle. A vac leak near or in the line to the MAP on the other hand, will cause an overall 'rich' condition.

Another clue, any vacuum leak will try to increase idle speed - intern causing ECM to command IAC counts to 000. (normal is 009 to 021 although up to 050 is allowed)

If no vacuum leaks found, suspect a problem with your new injectors. Did it run better with the old ones?
 
Merk

Merk

Donating Member
Guys-

Thanks for the replies and help. Turned out I had a bad ECM. Didnt take long to narrow it down...as the truck got worse each time I reset the ECM. The last straw was a 2K rpm idle in park, and a 500rpm idle in drive. Way wacky.

Here's my parts list:

Updated ECM : 16198263
Memcal BBZB 1580 : 16181579
Bracket, ECM upper : 15664699


And, while I was at it:

Calibrator, Veh spd sensor (CBY) : 16124465

Spent 10 mins burning in the new memcal, the idle is solid, no surges, no spits, sputters. Me happy! :D

Thanks again all

Merk
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LovelyWendie99
 
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