O/T 350 chev Sensor question RRich - Off-Road Forums & Discussion Groups
Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

Reply
 
LinkBack Thread Tools Display Modes
post #1 of (permalink) Old 09-18-2006, 05:11 PM Thread Starter
I Might Just Know What I'm Talking About
 
GoldToyBox's Avatar
 
Join Date: May 2002
Location: Selma,CA in the middle of the vineyards, Central California
Posts: 1,654
Thanks: 0
Thanked 0 Times in 0 Posts
 
O/T 350 chev Sensor question RRich

I thought I had saved an old Rich post on this but I can't find it.

1990 K-1500 4x4 Z71 extra cab pickup, 350cid, w/700r auto, California emissions

I just installed a new motor & tranny (250 miles so far). It's running rough at idle and has a very bad 'stumble'/cut out/miss/stall. When I travel between Fresno (250 ft elev) and my home (7000 ft elev)the problem is between 5000 ft & 6000 ft. The idle problems seems to be all the time (rough & will die at stop lights). I suspect the sensor? Which ones and where are they?

Thanks for any help/advice/suggestions.

Rockin On
GoldToyBox is offline  
Sponsored Links
Advertisement
 
post #2 of (permalink) Old 09-18-2006, 06:27 PM
**DONOTDELETE**
Guest
 
Posts: n/a
Re: O/T 350 chev Sensor question RRich

Without a scanner, this will be a tough one....
But my first vote would be a major vacuum leak....and, are you SURE you got the plug wires hooked up right?

I have a 93 in my jeep...basically the same as what you have......if your Check Engine lite is not on, you will really need a scanner to find the problem...most auto stores will scan it for you for free....the figure they will be able to sell you the part you need....
post #3 of (permalink) Old 09-18-2006, 06:47 PM Thread Starter
I Might Just Know What I'm Talking About
 
GoldToyBox's Avatar
 
Join Date: May 2002
Location: Selma,CA in the middle of the vineyards, Central California
Posts: 1,654
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: O/T 350 chev Sensor question RRich

Wires are new and in correct location.
Looking for Vac leak but nothing yet.
GoldToyBox is offline  
Sponsored Links
Advertisement
 
post #4 of (permalink) Old 09-18-2006, 06:49 PM
Way Outta Control
 
Join Date: Sep 1999
Location: The Palouse
Posts: 13,432
Thanks: 1
Thanked 3 Times in 3 Posts
 
Re: O/T 350 chev Sensor question RRich

[ QUOTE ]
Without a scanner, this will be a tough one......

[/ QUOTE ]

Nope, it's OBDI compliant, just short pins A&B together of the ALDL connector with a paper clip to recover the codes.
LEVE is offline  
post #5 of (permalink) Old 09-18-2006, 08:19 PM
I Might Just Know What I'm Talking About
 
jdoggmoney's Avatar
 
Join Date: May 2003
Location: Nebraska
Posts: 1,806
Thanks: 0
Thanked 1 Time in 1 Post
 
Re: O/T 350 chev Sensor question RRich

Larry's right.. again. A couple of things to check. Did you do anything to the dist. on the swap? The modules in those had a bad habit of heating up and having corrosion grow all over them and between them and the base.

As also stated by others, check for a vcuum leak around the TBI base. The TBI gasktes also had a bad habit of getting sucked in and creating an awful leak. This may not trigger a code, but could cause the driveability issues you describe.

Did you check or replace the fuel filter at the time of the swap? The factory pumps work well, but it seems as though a clogging filter was very hard on them. Even if changing the filter helped, 8 out 10 the truck was back fairly quick for a fuel pump R&R.

I have a FSM for 1995 that should have a trouble shooting section for your code if it says there is one.
jdoggmoney is offline  
post #6 of (permalink) Old 09-18-2006, 08:25 PM
Way Outta Control
 
Join Date: Sep 1999
Location: usa
Posts: 10,815
Thanks: 0
Thanked 1 Time in 1 Post
 
Re: O/T 350 chev Sensor question RRich

I kinda doubt you'll find any codes, scanner or A&B. If what I think it is, it's normal.

You start at low altitude, and want it to keep running fine to 7000 feet?

Uh, let me ask - how many times do your ears pop on that trip?
The ears pop to compensate for the change in Barometric pressure. Your engine can't pop it's ears.

Try something - about the time it starts to run bad, or even a little before - stop in a safe place. Turn the key off, wait 5 seconds, turn key on but don't start for 5 seconds, then start it up. It'll probably run almost as good as it did when you started up the hill.

Reason is - you don't have a separate barometric sensor. As you go higher the computer doesn't know that there's less air up there. When you first turn the key on, the ECM quick "looks" at the MAP sensor before you crank it. It stores that information as the BARO reading - then compares it to the MAP for calculations. But when going up that high eventually it's comparing AZP to old information.
Cycling the key resets the BARO reading.
I think you'll like how it runs afterwards.
Same thing going down the hill.

The older systems used a BARO sensor, but it was another thing to go wrong.

And - make sure the vacuum line to the MAP sensor is all by itself. No Teeing other things into it, small diameter - the hard plastic stuff is preferred (harder to route, but it doesn't collapse,) and as short as practical.

The hard plastic lines - use small diameter regular vac hose splices on the ends or to connect with.

Let us know --
RRich is offline  
post #7 of (permalink) Old 09-18-2006, 10:09 PM Thread Starter
I Might Just Know What I'm Talking About
 
GoldToyBox's Avatar
 
Join Date: May 2002
Location: Selma,CA in the middle of the vineyards, Central California
Posts: 1,654
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: O/T 350 chev Sensor question RRich

Thanks for help everyone

The distributor & coil & plugs & wires & water pump & starter & fuel & air filters are new. I have to get a smog test next, so I need to find this problem.

Checked around the Throddle body and found no leaks yet (using propane but ran out).
I still suspect a small vac leak for the idle but the stalling at speed & load seems like sensor to me. I'll do some more checking tomorrow. Got a code reader & more propane coming.

I've not notice any problems going down the hill .... coasting & braking most of the way. Motor working much harder going up hill.

RRich I remember something about cleaning the sensors?

Rockin On
GoldToyBox is offline  
post #8 of (permalink) Old 09-19-2006, 08:58 AM
Way Outta Control
 
Join Date: Sep 1999
Location: usa
Posts: 10,815
Thanks: 0
Thanked 1 Time in 1 Post
 
Re: O/T 350 chev Sensor question RRich

For the rough at idle - at the cap - one at a time - pull each wire off - notice the RPM drop. Try to find WHICH cylinder is the culprit.
Hold your hand over the carb - more and more to choke it off - or use propane to richen it up?

Doesn't get smoother?
Swap that plug out. Swap that wire out.

Helps? Look closely at the intake runner at any vacuum ports - use propane on all of them. Pinch the hoses off on that runner oe at a time.

The altitude problem - going uphill you are under more of a load, more noticable. And the altitude makes it richer - the computer system is not as capable of leaning as much as it can richen.

Going downhill it's just the opposite. You won't feel it as much.
You aren't alone - there are millions of other vehicle doing the same thing all the time.
Key off, key on, resets the Baro data. Just like re-booting your computer here when it's slowing down or doing strange things.

Sensor cleaning - BUT NOT THE TPS! - get a spray can of intake cleaner for injection cleaning. Remove the sensor, spray it down with it - while still wet, I run them under cold water briefly to remove the cleaner.

If you have a MAF Mass AirFlow Sensor, make sure all the ducting between it and the throttle body is tight and well sealed - no leaks, rips etc. -- very important!
RRich is offline  
post #9 of (permalink) Old 09-19-2006, 02:56 PM Thread Starter
I Might Just Know What I'm Talking About
 
GoldToyBox's Avatar
 
Join Date: May 2002
Location: Selma,CA in the middle of the vineyards, Central California
Posts: 1,654
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: O/T 350 chev Sensor question RRich

OK,
Code Reader shows only Code 12 (normal)

Removed wires one at a time with no noticable changes.

Unplugged the MAP sensor, no improvement.

No MAS on this rig.

Cleaned up around & in TBI (was pertty clean already)

Checked timing? Huh???? about 20 degrees advanced ???? WTF??? This is at idle with everything connected.
Checked the manual, "set timing as per the label on the radiator supports" Huh???? no label there? Found another reference to disconnecting the timing via a "Tan wire with black strip" that exits the loom near the distributor. Can't find that either?

Does anyone know what the timing should be & how to set it? Needs to pass Calif smog.

Thanks
GoldToyBox is offline  
post #10 of (permalink) Old 09-19-2006, 03:07 PM
**DONOTDELETE**
Guest
 
Posts: n/a
Re: O/T 350 chev Sensor question RRich

There is a connector on the main harness near where the harness connects to the engine...single wire in and out....it looks like it's just taped to the side of the wire bundle...

Unplug that wire and then check/adjust the timing. Set for 0 deg TDC.

Don't forget to connect it back up when done.
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Off-Road Forums & Discussion Groups forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome