1990 No Up Hill Power?

[speedygonzales]

Back to squares. Did you ever determine if it is firing on all cylinders?

[LynnJr]

If I pull a plug wire while its at idle they all seem to lose a little rpm.Compression is good and none of the plugs look bad.
Lynn

[crazy-101]

I have a very similar problem on my '95. It will cut out and chug going up hills and shake almost like a misfire just going down the road and when accelerating it will almost gain and loose power at regular inter voles. Did a vaccuum test and the needle was bouncing around. Code in the ecm is to lean but is running to rich. Has exhaust leaks in front and behind the o2 sensor

I have replaced:
Fuel filter
Distributor, cap, rotor
injectors
injector connectors
tbi full rebuild
egr valve and solenoid
ignition coil
changed plugs twice burnt plug on the #2 cylinder
temp sensor x 2
intake
intake gasket
oil pressure switch
idle air control valve

I have been told that I will need to pull the heads and have them machined and/or a valve job done. The old intake manifold was warped and replaced in April. May be your only option to do heads as well. If anyone else has a suggestion please feel free to speak up.

[LynnJr]

When I first installed the motor it had a valve seat problem and even though it was a brand new chevrolet crate motor they wouldn't fix it.
I had a local machine shop go through the heads and my receipt shows $456 for heads with under 300 miles on them at the time.
I work for the postal service so right now its hard getting any time off to work on it.
After the first of the year I will replace the distributor assembly with a points style distributor with new wires,plugs and coil to see what happens.
If that doesn't do anything I'll put a old style single plane manifold and Holley 750 on it.
That will eliminate most of the factory computer garbage from the equation and atleast get me up and running smoothly.
I already have all the parts so its just installation time.
Judging by your post you would probably be better off doing the same thing.The only thing needed is to change the center bolt angle on the manifold and you can do that with an ordinary drill and a 3/8 bit.
Lynn

[speedygonzales]

Originally Posted by crazy-101

I have been told that I will need to pull the heads and have them machined and/or a valve job done.

Originally Posted by LynnJr

When I first installed the motor it had a valve seat problem

Valve problems are very simple to find or confirm with a leakdown tester. Not expensive to buy or use as a loaner from the auto parts stores. You will need a compressor to use it.

Originally Posted by LynnJr

After the first of the year I will replace the distributor assembly with a points style distributor with new wires,plugs and coil to see what happens.
If that doesn't do anything I'll put a old style single plane manifold and Holley 750 on it.

I think before you go throwing money at the problem, why not look at the distributor advance curve. You know at idle how much advance you should have. It's easy to find how much you should have at a high RPM. Then simply check with a timing light.

[LynnJr]

Speedy
I already own the distributor and manifold so I'll only be out a manifold gasket to see if that fixes things.When the motor was running right it had the distributor and carb on it not the TBI.

How are you checking the distributors advance curve? Are you breaking the distributor connection to check it? I ask because once the wire is hooked it no longer makes much sense when looking at it with a timing light.
Lynn

[speedygonzales]

As engine RPM goes up, the ignition firing must advance to keep the power output high. If the advance is not happening regardless of whether it is under computer control or simply mechanical, the engine looses power. This can be evidenced by using a timing light. If the engine has a timing indicator so much the better. If it does not, make one. Either way the ignition timing must advance and evidence is there.

See ya

[LynnJr]

Speedy

I agree and will give it a try.The engine has a timing tab and the balancer has a paint stripe on it.
I was just thinking I did this several years ago and it wasm't like a conventional points or magneto type ignition system.I thought with my failing memory that one the computer took over the advance curve was really high.
I will give it a try and post back.
Lynn

[LynnJr]

Don't know if I am doing this correctly or not but I got 8 degrees at idle and it went out of sight when I pushed on the throttle.I am using a variable timing light so I can dial it up but I didn't find it anywhere.
Lynn

[speedygonzales]

You never noticed spark knock did you?

[ChevyTech]

If it has 10 PSI fuel pressure like you said, and the catalytic convertor has been remove, I think you guys are correct to question ignition timing.

The Knock sensor contains a piezoelectric crystal which causes a voltage to be produced. Loose components on or in the engine can cause the knock sensor to create a voltage and the system may interpret this as pinging. The system retards the timing because it determines it is pinging.

The spark control module (Knock sensor module) monitors the knock sensor, and sends a signal to the ECM that, retards the timing if it detects pinging, and advances the timing when no pinging (knock counts) is occurring.

Loose torque converter bolts, on a truck with an automatic transmission, can cause a false knock signal to be detected. Anything that rattles on or in the engine or transmission has the potential to cause false knock counts.

Running plug wires close and parallel to the knocks sensor wire can cause problems.

The computer does a self test of the knock sensor circuit when certain criteria have been met after the coolant reaches 189F. If you run a cold thermostat the engine may not be reaching the threshold temperature to run a self test to set a trouble code 43 to signal that there is a spark timing control problem.

You could unplug the knock sensor and see if it set s a code 43. If it runs better the sensor unplugged you may have found them problem area. Driving for an extended period with the knock sensor unplugged could cause pinging and or damage.
It should set a code 43 if you drive it at operating temperature with the knock sensor unplugged.

[LynnJr]

I am not running the factory 190 degree thermostat.I think it is about 165 degrees maybe a touch hotter but it definitely isn't 190 degrees.

I will replace it this sunday and report back.

Is 15 degrees about right on the timing with the wire connected? I ask because along time ago I thought it ran out of sight once the wire was connected and now it doesn't seem to move a lot only 15 degrees.

Also should I just install a new knock sensor?
If my memory is any good the connector on the sensor may need to be replaced as well.Hopefully somebody sells this wire and connector?
Lynn

[ChevyTech]

Is 15 degrees about right on the timing with the wire connected? I ask because along time ago I thought it ran out of sight once the wire was connected and now it doesn't seem to move a lot only 15 degrees.

I would consider anywhere from 12 to 22 degrees normal at idle with the wire connected.

You can tap on the passenger side exhaust manifold, lightly with a hammer, and watch the timing retard if everything is working right.

Testing saved from an old post of mine:
When testing the knock sensors, some automatic trans equipped vehicles, the trans must be in gear. Jack it up, support the rear axle with stands, and then test the sensor. Let the engine warm up and go into closed loop. Have a helper put it in drive with their foot firmly on the brake, and watch the timing while you tap on the exhaust manifold with a hammer, to simulate a ping.

Also should I just install a new knock sensor?
If my memory is any good the connector on the sensor may need to be replaced as well.Hopefully somebody sells this wire and connector?

If the connector for the knock sensor needs to be replace, they are available.

If you do replace the knock sensor:
Knock sensors are more fragile than they look. I like to only tighten them by the hex on the base on the sensor, not by the hex on the plug end of the sensor. Do not use Teflon tape on the knock sensor
threads.

I would not replace the knock sensor at this time. If the truck lacks performance from this system it is because of to many knock counts – not to few knock counts. Bad knock sensors usually fail to produce the knock counts they should.

I am not running the factory 190 degree thermostat.I think it is about 165 degrees maybe a touch hotter but it definitely isn't 190 degrees.

If you are running a colder thermostat and the engine is running at the colder thermostat temperature, then it is hurting fuel mileage, and most likely contributing to carbon build up. This engine could have excessive carbon build up causing pinging which will retard the timing. It could also have heavy carbon deposits on the valves and ports which will cause it to run poorly, lack power and idle rough.

[LynnJr]

I bought the thermostat the gasket for it and some silicon to install it today.I will put it in this sunday.
One thing I noticed is the knock sensor didn't have the wire hooked up to it at all.
I don't know if that was my problem as the store didn't have one in stock but it should be here before sunday.My fingers are crossed.

I also read another post here saying I should have a good ground at the coolant sensor next to the thermostat housing.I don't have that ground and the one at the local store is huge in comparison to what the factory strap is like.Does anybody have a name or part # for that braided line or is it a dealer only item?
Lynn

[ChevyTech]

One thing I noticed is the knock sensor didn't have the wire hooked up to it at all.

Your truck has plenty of problems, and with no wire on the knock sensor, and no codes from it, makes me wonder how many more issues there are.

This TBI system is very dependent on the knock sensor to control the timing, which is constantly being adjusted, when the system is working correctly.

Does the check engine light come on when you turn the key on without cranking the engine?
Have you checked it for trouble codes?

I also read another post here saying I should have a good ground at the coolant sensor next to the thermostat housing.I don't have that ground and the one at the local store is huge in comparison to what the factory strap is like.Does anybody have a name or part # for that braided line or is it a dealer only item?

The coolant sensor in the intake manifold is a two wire sensor. One wire, of those two wires, is a ground wire. The ECM and sensors end up grounding to the engine at the studs on the front of the intake. Sometimes the thermostat housing has one bolt and one stud, with some grounds to that stud. A stud at the thermostat is a poor place for a ground and I don't suggest using as a spot to connect any ground wires. I would move any ground wires to a stud at one of the intake bolt holes.

I bought the thermostat the gasket for it and some silicon to install it today.

From the factory, most, if not all TBI V8s came with a rubber seal on the edge of the thermostat and did not use a gasket or silicone.

[LynnJr]

When I plugged off the EGR vacuum lines the service engine soon light came on and it through a code that I erased.
I have been replacing external parts trying to solve the issue and I removed most of the connections at that time thinking something was loose.Th connection at the knock sensor got my attention because it is no longer fully round there is a chunck of it missing and it didn't snao in firmly.
I don't know how long it has been unhooked but I have a new one on its way and hopefully I am back in business.
The original water neck had erroded some time ago and I don't know if this one takes an O-Ring or gasket.I will get both to be on the safe side.

While I was watching the timing at night I did notice the timing would change at idle.I thought it was the timing light connection but maybe it was another issue.
Lynn

[LynnJr]

I soldered in the new knock sensor plug and took the truck for a test ride.It feels like it is getting better but still has a low end miss that clears up as the RPM increases.
On initial turning on of the key the service engine soon light comes on for a short period then goes off.When I am driving it the only light that comes on is the shift light.
I ran the codes and only get code 12
It started raining but when it stops I'll do the thermostat.
Lynn

[brownsville]

hey bud, ive had this problem for the last 6 weeks. Turns out the wires going to the starter were burnt through at the manifold. I removed the started rerouted the wires and taped up the bad places. It was arching on the exhaust manifold and would loose power ie feel like i was pulling a heavy load even on flat ground. Problem is fixed now and shes running like a scalded dog. Hope this helps and its something stupid like it was on mine

[MadManAndrew]

I would just like to throw out that my K10 was acting like this when I got it and it was indeed the timing and only the timing.
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[LynnJr]

I didn't get the thermostat in today but I did tape up the starter wires.They were all cracked from the heat.Its running much better but still has some low end missing issues.
I will pull an easy to get to plug and see what my gap is.From the factory this crate motor calls for 0.035 with a points type distributor and 0,045 with a HEI type distributor and I want to make sure I have them at 0.045
Lynn

[Boog]

So, did these problems start up before or after the truck went for a swim?

[LynnJr]

20 years later
Lynn

[ChevyTech]

Originally Posted by LynnJr

... It feels like it is getting better but still has a low end miss that clears up as the RPM increases.
... Lynn

It sounds like there are many problems with this vehicle.

A cylinder that misfires needs to be repaired.

Here is how a misfire can affect the system:
These systems work great when every thing is right but they have a big flaw. Once the engine misfires for any reason it throws the system in the rich direction. This system watches the O2 sensor, but the O2 only will see how much oxygen is in the exhaust stream NOT burnt gas. When every thing is right the O2 knows just how much of the oxygen should have been burned by combustion. If the system gets a little to rich all oxygen is consumed. If it gets to lean there is not enough fuel to burn all the oxygen and there is more oxygen in the exhaust. Once it misfires, there is way more oxygen in the exhaust, because none got burned in a cylinder. The system thinks it is to lean so it gives the engine a richer mixture. The richer mixture often makes it misfire more (especially if it is cause by weak ignition, bad plugs…) so it dumps in more fuel. Now it is so rich the plugs and O2 sensor get soot on them. It misses more. The system goes richer and richer.

[Ripsaw]

Originally Posted by ChevyTech

It sounds like there are many problems with this vehicle.

A cylinder that misfires needs to be repaired.

Here is how a misfire can affect the system:
These systems work great when every thing is right but they have a big flaw. Once the engine misfires for any reason it throws the system in the rich direction. This system watches the O2 sensor, but the O2 only will see how much oxygen is in the exhaust stream NOT burnt gas. When every thing is right the O2 knows just how much of the oxygen should have been burned by combustion. If the system gets a little to rich all oxygen is consumed. If it gets to lean there is not enough fuel to burn all the oxygen and there is more oxygen in the exhaust. Once it misfires, there is way more oxygen in the exhaust, because none got burned in a cylinder. The system thinks it is to lean so it gives the engine a richer mixture. The richer mixture often makes it misfire more (especially if it is cause by weak ignition, bad plugs…) so it dumps in more fuel. Now it is so rich the plugs and O2 sensor get soot on them. It misses more. The system goes richer and richer.

Great explanation, thanks !

[ChevyTech]

Originally Posted by Ripsaw

Great explanation, thanks !

You're welcome Rip!