1993 K1500 runs terrible when hot

[Thor1993]

Hi guys,
I am a new member here. I need a little help with my 1993 K1500 4.3L truck. Maybe one or more of you have been through this already. I have sent a few private messages to old_ master and I have put an Ac Delco cap & rotor on with dielectric grease as he recommends
I thought I would start a thread on this also.
Well here is the problem, my truck runs like a new truck for 3-4 miles (open loop maybe) then runs terrible after 3 miles (closed loop maybe) After 20 miles on freeway the pass side exhaust manifold is red hot. (I guess this is probably why I have a cracked exhuast manifold.) So until I fix it I am only using it for plowing. I am thinking about a new intake gasket. However, I spayed starting fluid all over the intake but speed never increased. The first time I did this I found a bad PVC line and discovered a bad throttle body gasket. This has been fixed. Here is a list of ideas I have already tried. Next I am onto the knock sensor.
Here is a little history
cc = carquest az = autozone
I made a spread sheet but it won't tranfer here so the date is way over on the right and the repair is on the left sorry for the confusion

11/9/2011

new batt cable
cc

3/3/2012

171,319

new plug wires, 5yr warranty,
cc

5/18/2012

171,600

new fuel pump & all gas lines
cc

5/18/2012

171,600

new fuel sending unit
cc

8/21/2012

new catalytic conv

9/22/2012

New coil
cc

10/1/2012

177,000

new new plugs, wires, cap & rotor
az

10/15/2012

new O2 & exhuast

12/23/2012

new coolant temp sensor & thermostat
az

11/1/2013

179,300

new plugs, wires, cap, throttle body gasket, belt tensioner, elbow for PVC line

12/22/2013

179,900

MAP - tested OK

12/22/2013

179,900

TPS - tested OK

12/22/2013

179,900

Temp sensor - tested OK

12/22/2013

179,900

new temp sending unit for gage

12/27/2013

179,900

new EGR valve & vac lines

12/24/2013

179,900

new O2 sensor

1/2/2014

179,900

new ECM

1/9/2014

179,900

new AC Delco cap & Rotor



This truck is driving me crazy. Any ideas are welcome.
Thanks very much,
Greg

[j cAT]

the exhaust manifold crack my be the problem. with a crack the KS will retard timing.also the O2 will report a lean condition to the computer. this will be noticable after the open loop ends and the closed loop begins.

the ICM should be removed and call AZ to see if they can test it.

[Thor1993]

Some more data on the issue in case some of you are thinking about this one….as I read other threads and see suggestions on other similar problems I will post the data on my truck here.
· It is probably not a tank of bad gas, I have been through several tanks of gas and added ISO heat and dry gas to get rid of water but there wasn’t any in the tank because I had to replace the o-ring on the tank and I was able to look inside.
· I have owned the truck for 5 years and it has been a good runner until a few months ago. Granted a 4.3L lacks power on a good day, but before, at least it would run 75 mph with no problem.
· The motor is bone stock no mods at all. No K & N filter, no disconnected emissions etc.
· Both injectors seem to spray a nice “cone” of gas mist.
· It idles perfect, it plows perfect(I live in Michigan and have been plowing my driveway), it starts right up. It just won’t hold 50 MPH on the freeway and struggles to get there after it drives 3-4 miles.
· The distributor shaft has no side to side play but does have a little up and down play. The distributor had a sticker that said something about voiding the warranty so perhaps the distributor is a replacement.
· The crack in the exhaust manifold closes up when the motor is hot.
· The exhaust does rattle on crossmember , I will fix this just to make sure not causing issue with knock sensor.
· Speaking of knock sensor, I will look for plug wires running to close to wiring harness to make sure we are not getting stray unwanted electricity to the ECM.
· The ground on the temp sensor checks OK

J cAT - The crack is huge but it closes up when the motor is hot, Do you still think that will cause issues with Knock sensor? and what is ICM?
Thanks, Greg

[maxwedge]

Sounds like it could be running too lean, how about the fuel filter?

[Thor1993]

Maxwedge,

Well it has been 1 1/2 year since I replaced it and it has about 8,000 miles on it so I will add this to the list ASAP since it is cheap. Should be easy I put in all new lines 1 1/2 ago.
Thanks, Greg

[j cAT]

exhaust manifold leaks screws up the computer fuel mixture sensing / control. also the sound retards the timing because the KS picks up too much noise.

what this will do is dump more fuel into the engine then your converter will over heat.

melt.

fix the manifold then if it lacks power remove the upstream O2 sensor / LEAVE HOLE OPEN ... test run to see if power returns..if so then the exhaust is restricted converter or muffler ..

[Thor1993]

j cAT Thanks I will shop for a manifold and get it installed. When I had a missing donut on the Y pipe it ran terrible but then it was a big leak.
Greg




also how does the "thanks" thing work that I see below a poster's name??? I am new here and don't know how this works and I certianly don't want to be rude!! I really appreciate the help you guys give from this site!

also, I sent a private message to member old_master but I get a page not found What am I doing wrong?

[Schurkey]

1. Is there an O2 sensor in the cracked exhaust manifold? I'd have expected this truck to have a single O2 sensor, in the driver's side manifold.

2. When was the last time the ignition timing was verified? Initial advance is easy, but does the timing advance with RPM? How much? Glowing exhaust manifolds are typically due to retarded timing, although incorrect fuel mixture can do it, too. An outright misfire can load the exhaust with fuel and air, the hot exhaust from other cylinders ignites it.

3. Does the engine have an air pump? Does the air pump switch from upstream injection (into the exhaust manifold) to downstream (closer to the converter, or on some vehicles, into the air cleaner)? Injected air into the exhaust manifold once the engine has warmed-up, can overheat it.

4. If you remove the PCV from the valve cover, and spray aerosol carb cleaner or (unlit) propane from a small torch into the open grommet, does the engine RPM change? This could signal a blown intake manifold gasket, where the gasket leaks at the bottom of the port, pulling excess air into the cylinder.

[Thor1993]

Schurkey - Thanks for the ideas, here are my answers.
1. The truck has one O2 sensor just before the cat.
2. The timing was checked last week, with engine at operating temperature with the wire on firewall unplugged. I set it to 0 as the sticker on shroud specifies. (actually I have never moved it, it has always been at 0) RPM drops when I unplug wire. I have not checked to see if balancer has spun on yet. When wire is plugged in, the timing advances maybe 20- 25 degrees as you rev up the motor as I recall. The timing mark is steady and does not float around. All the spark plugs looked good and consistent when I replaced them in November 2013. Another words no obvious miss firing or fouled plug.
3 No air pump.
4. I will try this; I was wondering how to check for this without pulling the intake off. Great idea.

Unfortunately, I have to leave on a business trip today and I will not be back until Friday to try the propane. I will try that next week end. I also bought an AC Delco fuel filter for it just to rule it out.

Thanks for all the ideas, they are greatly appreciated.
Greg

[j cAT]

with the use of a small propane torch and placing a hose on the end probing for vacuum leaks is a better way than spraying carb cleaner on the engine because carb cleaner damages electrical/plastics etc...

[Thor1993]

Hi Guys,

news flash!!

I am back from a businees trip and being sick so now unto the truck again. I pulled off the PCV valve at the valve cover and tried propane but no change in RPM so I tried propane in pcv valve and no change either. Hmmm.... that seems odd so I carefully sprayed starting fluid into pcv valve and immediatly the rpm changed. So I sprayed a little into the valve cover and no change. So maybe the intake gasket is OK underneath?? I am so disappointed. I thought this was going to be it!! My son said funny things happen when your intake gasket is bad and I thought this would confirm it. Well, I still need to put the new fuel filter on it.
any other ideas?? ( I have not done exhaust manifold yet.)
Greg

[rhandwor]

Have you actually checked the fuel pressure. Their is a pressure regulator for this vehicle. They have a rebuild kit. These throttle bodies get dirty and have to be cleaned they sell a kit at the parts store. Get a loaner fuel pressure test kit at Auto Zone or Advanced Auto. I have an adapter for these remove the filter and it connects at this point.
http://www.rockauto.com/ Search for throttle body repair kit. The Standard had what I remember as the pressure regulator diaphragm. The Airtex didn't have this part. Napa sells Standard products.

[Thor1993]

Actually no I have not checked fuel pressure. I have a fuel pressure tester I bought several years ago. I will put it in line and test when I replace the fuel filter this weekend and report back.
Thanks for suggestion.
Greg

[Thor1993]

Latest update!!!

Well we can eliminate the fuel filter as the problem. I put a new ac delco fuel filter in today and no change.

Also today I ran a vacuum gage into the cab and went for a ride. I am getting steady 18 at idle. 0-2 when I stick my foot in it and when I let off I get 20-25 for a second and then back ro 18. At any reading the needle is as steady as a rock.

Then I went to the auto store and picked up the fittings and gas line to run a fuel pressure gage and see what is going on. That test is next but I ran out of time today.

It has been a blizzard here in Michigan so I have not gotten to the junk yard to look for a exhaust manifold yet.

Thanks Greg

[Schurkey]

Originally Posted by Thor1993

Then I went to the auto store and picked up the fittings and gas line to run a fuel pressure gage and see what is going on.

Huh? Photos?