NeedSpeed

I have a '92 LT1.

When it's cold it seems to run ok. Recently I was getting hesitation under hard acceleration. It got worse to the point where it hesitates real bad the hotter it gets. Even very light acceleration causes it to hesistate. It gets to the point where it hardly wants to idle.

When it's cold it's ok.

Fuel pump? I just changed the fuel filter.

I've got 6-mos on a new Dynaspark, plugs, and wires. Just changed out the O2 sensors as well.

Yellow95

Sounds electrical to me but you seem to have replaced most of the parts. How about the coil?

NeedSpeed

The coil is stock. It's got 145kmi on her too.

I didn't think about that.

bogus

oh, yea... coil and ignition module... with those miles? replace'm.

if it isn't them, they are still new. but more then likely, the coil or module are getting heat soaked.

SunCr

Coolant temp signal may be off. If the PCM believes the engine is cold, it will add too much fuel. I'd verify the temp with a scanner.

NeedSpeed

Actually, the temp sensor is only about 6-mos old too. I've watched the temp, and it's about normal.

Are a coil and ignition module Autozone type items?

JAKE

He's referring to the coolant temp sensor that the ECM uses, not the one that shows the temp on the dash.

Two different animals and the one the ECM uses is critical for the ECM to send the correct timing and fuel signals.

Jake

NeedSpeed

Well, I changed the temp sensor in the water pump which is the primary sensor.

What other sensor would the coolant gauge use?

SunCr

Gage sender is threaded into the right cylinder head. A scan will verify the signal. I'd verify the air temp too by comparing both on a cold motor (should be close to ambient) and then monitoring as the engine warms up.

NeedSpeed

That's a new one on me!

SunCr

If the signals check out, you might also want to ohn out each injector hot and cold. Specs are 10 ohms or greater, but they should all read the same hot and cold usually around 17 ohms.

NeedSpeed

I've been considering just replacing them all anyway as they are also stock.

What size are the stock size for them?

JAKE

Here I go again.

Changing parts in the hope of hitting on the one that's causing the problem isn't the way to go about it.

A data logger running when the problem occurs will identify which sensor is out of range.

Changing injectors may well be an unnecessary expense, not to mention the work involved. Just use a meter to check the resistance; your injectors may well be fine.

Why spend hundreds of dollars and many hours of work changing injectors only to find that the engine still "runs like crap". You'll still have to find and fix the cause after all that.

Please, don't fall into the trap that so many others have, (becoming a parts changer). I wish I had a dollar for every post I've read - "I've changed this, and changed that and changed the other, but still . . ."

How'd you feel about a doctor you visited complaining of a headache and he immediately fired up the operating room to do brain surgery on you?

Same principle, run some tests, check for proper operation of the parts and sensors, find the one(s) that's not performing as it should, then repair/replace it.

A ScanTool will give you most of the information you'll need. A test light and a voltmeter will give the rest.

Just my suggestion.

Jake

NeedSpeed

Well, you're right and I'm generally not one to just change parts. I'll check the injectors, but I don't have a scan tool. I guess I need to buy one.

My car is 13 years old and other than the tires, brake pads, opti, belt, hoses, water pump, plugs and wires, o2 sensors, and the temp sensor it is all original at 145K miles.

I just now bought rotors, hubs, and bearings which I was going to change until it started running crappy. Yep, the current units are stock.

Oh yeah, I did change the u-joints on the half shafts and one clutch. Still not bad for a '92.


I just figured with some parts, they probably should be changed after that many miles. I was considering a new set of injectors before this problem occured, which is why I said as I did. If they're ok, I guess I could just get them cleaned.

NeedSpeed

Ok, strike that, this just happened cold:

I just started it and it freaked out on me. Ran ok for a second, then the tach started jumping.

I shut it off, turned it back on. Running horrible, backfiring. It will stabalize some, but reving it up in neutral hesitates bad.

Sounds more like an Opti, doesn't it?

No codes.

SunCr

Could be - but it could still be a bad temp sensor - or an injector - or a fuel pump or pressure regulator as missing is often a fuel delivery problem on an injected engine. Of course it could be something else - really difficult to tell without running a few tests.

NeedSpeed

Well, it managed to chill out and I was able to drive it home. It was ok as long as I accelerated lightly and kept a steady RPM. It was mostly highway on the way home, so it wasn't too bad. If I stopped, it didn't want to maintain idle very well.

I'll run what tests I can and see what comes up.

bogus

jumping RPM? running bad? no code? That's coil/ignitor.

The RPM data comes right off the tach filter, which gets its data from the coil/ignitor assembly.

Once the tach starts wacking, then I would look at the coil. Considering it's getting worse, I am more convinced it's at the coil/ignitor.

Call Chris at Superior Chevy, 1.800.728.8267, tell him you are a forum member... I am sure you know the drill.

NeedSpeed

Yeah, no code is what's surprised me. The tach doesn't always do that, but it sure went bezerk last night. I got a local Chevy guy that does me right. What about the Ignition Module?

JAKE

You can also run a TPS voltage check too.

With a voltmeter, engine off, check that the voltage increases in a steady fashion as you open the TB butterflies by hand. There should be no sudden jumps or dip in the voltage readings.

From what I've read, a digital volt meter ISN'T the best for this kind of test. If DVM is all you have though, give it a try.

Jake