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1996 caprice classic stone stock
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Discussion Starter #1 (Edited)
So I acquired my grandmas 96 caprice. I know the last "tune up" was done by my uncle cause the 1000 dollar bill was to much in his opinion, which probably means he did 2 plugs and 1 wire.



Anyway the car has 114k miles when I picked it up yesterday I drove it a few miles, jumped in it to run to the store it made it 2 blocks I started to accelerate from a stop sign and it suddenly sounded like an older engine thats dieseling after shut down. I backed outta it sound didn't change so I shut her down called my dad and we drug it back to my house with a strap.

Battery was at 11 volts and wouldn't crank so ASSUMING thats the problem (and probably a bad alternator) I charged the battery tried to crank it when I let off the starter its stumbling along just good enough to keep turning and thays it but its not knocking now, I'm (again) ASSuming, cause its cold so it can detonate. Cranked it over a few times hoping and praying its flooded or something (you know 馃槵馃檹馃槧馃檮) well last time it violently blew the intake apart, resonator on top of the engine the side blew out and the air box lid cracked and blew parts off

SO HELP.

I'm at a loss now cause that means the rotor has to be about 180* out but it will sit there and stumble along till boom.

I can't find (obviously its computer controlled) marks to even try to check the timing.

Is it possible for these things to have the timing jump like that?


Whats my next move besides just starting to throw parts at it.



Thank you for any advice and help offered and I'm still searching the forum for help
 

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1996 caprice classic stone stock
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Discussion Starter #2
I should add through all of this no check engine light or pending codes
 

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1996 caprice classic stone stock
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Discussion Starter #5
K this should be fun since I'm not familiar with this optispark, gonna be slow going trying to check all the signals.

It appears to have fuel pressure since it blew the airbox lid and resonator on top of the engine apart, but when I start with it I was going to check pressure. so once I get this sorted ill have to find those.

IF these screws backed out that I've seen talked about, where are they? on the rotor or down under where the optical wheel is? Can I just put them back in or is the unit trash once they back out?

Thank you guyz
 

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You'll need to pull the water pump to access the opti.
I can't find (obviously its computer controlled) marks to even try to check the timing.
I did this on a whim.
198373


Timing light does not make an exact match to the logger but it's useful for sanity checks.
 

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1996 caprice classic stone stock
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Discussion Starter #7
So I checked fuel pressure its about 45 lbs at the rail.

Yanked the fan and shroud off just trying to familiarize myself with what's where on this engine.
198383


Obviously thats the coil, and thats the ignition control module right?
198384

And thats the plug going into the optic sensors in the optispark right?


Those are the harnesses id use to diagnose it by signal voltage right? Does the water pump have to come off to do that too? Or just for the parts swap?
 

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1996 caprice classic stone stock
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Discussion Starter #8
I'm guessing I may have stumbled upon something. Pump was put on around 85k if I remember right, car now has 114k but it sat for probably 2 years occasionally getting started.

I was going to pull the harmonic balancer and just keep poking around since it'll have to come off anyway but it got to hot so I came back inside
198389
198390
 

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Before removing the OPTI please consider doing some tests first.

it suddenly sounded like an older engine thats dieseling after shut down.
well last time it violently blew the intake apart, resonator on top of the engine the side blew out and the air box lid cracked and blew parts off
If the car has not been running for quite a while it is possible that one of the injectors stuck open and fuel backed up into the manifold through a intake valve and ignited or the there was no proper ignition of fuel in the cylinders and un burnt fuel was pushed back into the intake hard enough to ignite. You might have some stuck open intake valves.

Without some testing you may go down the rabbit hole of adding new parts then questioning if the new part worked.

You were on the right track by using a timing light to check if the spark plugs, spark plug wires, coil, and ICM are working. You need a good battery and a battery charger to get good results. You can pull the injector fuses to reduce the risks while you check the ignition system. If the engine continues to get a lot of fuel with the injectors un powered you may have a stuck injector.

I have had non direct injection engines(and carbs) explode and fire up the intake. This had nothing to do with the timing, just un burnt fuel collecting. I have not had this happen with a multi-point sequential system but do not see why it could not.
 

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+1 on this ^^^^
You were on the right track by using a timing light to check if the spark plugs, spark plug wires, coil, and ICM are working.
I had these same symptoms (minus the intake blowout) with no codes - turned out it was a bad coil. Found it using a timing light on the coil wire to the distributor, showed erratic and intermittent spark behavior. Swapped the harness and distributor leads over to a spare coil and laid it by the ICM, turned the key and it fired right up.

Hope this helps -

Jim

Edit - Another avenue to look at if ignition checks out - a failed engine coolant temperature sensor (the one in the water pump) also gave me similar symptoms. It was reading way cold but didn't set a code -.severely flooded engine with no/rough restart. Just another thought.
 

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1996 caprice classic stone stock
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Discussion Starter #11 (Edited)
I have every intention to actually try to diagnose it and find out ehats wrong, that's why I checked stuff like fuel pressure first. But the fact that the video that is the top sticky, which I had seen before I even got the car, says the optispark is a 100k mile part this car has 114k and I'm dug in there already its getting a new one, along with a water pump, ignition control module and ill probably do a coil, along with plugs and wires weather I find an issue in diagnosing or not. But my question are they referring to the optical unit as a 100k part or the cap?

As far as injectors rail pressure doesn't bleed off like my ranger did when the injector was stuck open, and it just made for hard starts once running it was fine, I do want to ask is 45psi on the rail enough? Seems low to be based on other cars I've messsd with.

I would never have thought of the coolest temp sensor, but when I change the water pump I'll try to find its specs on here and ohm it out or just buy a new one and compare.


Oops didn't hit post yesterday



Now a bit of an update, tested all the electrical values right now everything was good so I pulled the cap and there were those 2 little screws laying in the bottom, put them back on and it fired right up so now I've got to start reassembling so I can putt around in it waiting for the new pump and cap
 

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hopefully you put red loc tite on those rotor screws...

you have an AC Delco Opti NEVER get rid of it as it has the Mitsubishi sensor (not available anymore). You can always harvest it to use in a cheap china clone should the bearing finally fail. It works now so keep it
 

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1996 caprice classic stone stock
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Discussion Starter #13
I did smear a bit on but I'm going to do a cap and rotor anyway since the rotor was pretty pitted up. And its still disassembled. Its the original 1996 optical unit, thats what you're saying don't ditch right? But the cap and rotor are no big deal?
 

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I did smear a bit on but I'm going to do a cap and rotor anyway since the rotor was pretty pitted up. And its still disassembled. Its the original 1996 optical unit, thats what you're saying don't ditch right? But the cap and rotor are no big deal?
yes cap & rotor are maintenance items just like any distributor. Standard Motor Products, brass terminals, C&R at rockauto

unfortunately MSD anything has gone to crap
 

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I can tell you that water pump has been leaking. Probably for a while.
 
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I commend you for wanting to diagnose and not just throw parts at it. Good man!

Two things:
  1. You'll never waste money by replacing the ignition coil and ignition control module (ICM) on an LT1. They are wear items. Use Delco, Delphi or Standard Motor Products parts. Never skimp on ignition components or sensors.
  2. Try hooking up the fuel pressure gauge again, and turn the ignition on but don't start it. Watch what happens AFTER you turn it off. If fuel pressure stays high for several minutes, your fuel system is fine. If it slowly drops, you may have a leaking injector. If it drops fast, and there's long cranking time, you have a fuel pump checkvalve problem in the tank. If a slow drop, I'd pull the fuel rail and injectors off the top of the engine and then pressurize the fuel system again. If any injector is dripping, there's your problem. This video is worth the watch. (76) Gran Turismo's 1996 C4 Grand Sport Corvette in the CAR WIZARD's shop! It's like being in the game! - YouTube
 

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1996 caprice classic stone stock
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Discussion Starter #18
The fuel pressure is good, 45 seemed a bit low since my Ford ranger and ls2 got ran around 60 psi but it holds there. It bled down to about 43 over a few min but then held 43 for 15 20 min before I went back to the car. I can watch it flutter when I crank the engine but it will flutter between about 35 and 55, I think thays more the gauge bouncing than the actual pressure going up and down.


As far as the waterpump leaking a long time, while time wise yes its been lea,ing a while but not many miles. And it makes sense now, she's in a "loaner" house while part of a lawsuit her house gets the outside remodeled. When I pulled the car out of the loaner garage I cleaned up a spot of oil from the drain plug and another spot that on the concrete looked like oil but was odd when I went to clean it it wasn't really oily but didn't give it a second thought at the time. Sad thing is the pump is "new" only has around 25 mayne 35k miles ok it, I have to wait till she gets back into her house this weekend to know the exact mileage and age, but its around 10 maybe 15 years old, and cost her something like 1300 to have replaced
 

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If fuel pressure stays high for several minutes, your fuel system is fine. If it slowly drops, you may have a leaking injector. If it drops fast, and there's long cranking time, you have a fuel pump checkvalve problem in the tank.
You have ignored the fuel regulator between the pump and the injectors. It can malfunction and return the fuel to the tank. All the people replacing their fuel pumps multiple times "because the new pump's check valve failed" should try the pressure test with the return line blocked. If the system now holds pressure it is the regulator not the fuel pump.

I have been chasing a malfunctioning fuel regulator all winter. Some mornings I got full pressure some days quick leak down, finally one day I got 15psi with the fuel pump on constant power but it was too cold to work on the fuel lines. One day when I had time it was going to zero in a minute and I blocked the return line. With the line return blocked the system held pressure till I lost interest in it.

So if a fuel system is losing pressure you have to check all the parts involved, pump, injectors, AND REGULATOR.
 

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Relating to Coil/ICM... It really pays to have a known good combo already mounted on a bracket to help narrow down ignition troubles quickly. In a crisis (by the side of the road ,for example) entire unit can be swapped out in 2-3 minutes.
 
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