Zralou

I'm about ready to take my .45 semi-auto and unload the clip into this vette....!!!!

This problem is soo frustrating i'm tearing my hair out. Car will start and run fine one day, then the next day, it won't start?. Some day's it will start, then won't start an hour later. Other days, it will start and I can turn it off and it cranks right back up.

During the no-start I loose spark, i've tried jiggling wires everywhere, but nothing changes.
I know its an electrical problem, but I can't for the life of me find out where the problem is. It doesn't matter if its hot or cold, sometimes it will fire, other times it won't.

I still have the annoying code 28 (quad drivers), and a code 64 (right bank O2), but nothing that points toward the problem.
I've owned this car since last august, and I haven't been able to use it, i've put less than 100 miles on it since purchase.
Not all of the down time is the fault of the car, my husband passed away in september, then we had winter, and i've recently moved house. But the weather is getting warm now and i'd like to get some use from this thing.

The car is a '93 model (LT1). I don't have a FSM, just the crappy Haynes. Previous owner claims he installed a new opti.
Anyone give me a few pointers in the right direction of what to check and look for?.

Sara Lou

rodj

http://www.mainstreamtopics.com/foru...rt-diagnostic/

Cliff Harris

The code 28 actually gives you a lot of information. You need to determine what is controlled by that quad driver and then look for problems in those circuits. I know a quad driver will set a code if one of the outputs is shorted. I don't know if it will set a code if it's open. You need a FSM (Factory Service Manual) to find out what to do when you get a code 28. There are troubleshooting procedures for each error code in the FSM.

The same applies to the code 64.

pcolt94

Sounds like the ICM (ignition control module) is acting up and a pretty common symptom. It's basically an amplifier that drives the ignition coil. A small solid state device that causes problems just like this. If it is bad, you will probably not get a code on this

The opti usually causes poor running and not so much a start and no start condition. If something major happens to it, it is usually will cause a no start condition at all.

You can remove the ICM and get it checked but with such an on and off problem, a check might not show up anything reliable. The only real check is substitution to find out if it is good or bad. It is an easy replacement. Heat sink it well and time will tell if you have found the problem. It is best to buy a GM unit regardless of where you get it from. The off brands seem to be causing a problem from what I have heard.

Zralou

Thanks for the link Rodj, it may just have found the problem. I went out to the car this morning (after a no-start condition all day yesterday), same no start condition this morning too. So I pulled the plug wire off the coil to test for power. After replacing the plug wire on the coil, the car fired right up, and fired up several tries thereafter.

Cliff I know I need a FSM, i'm just a miser when it comes to spending money . What year span do these manuals cover?, I have a '93 and my sister-in-law has a '92, would one manual cover both years?, if so I could probably talk her into going half on the cost.

Thanks Pcolt, I had a similar thought about the ICM, but shied away for now as most of what i've read, the ICM tends to become troublesome after it gets hot, but I probably will replace it soon anyway just to discount that as a contributory factor.

Sara Lou

pcolt94

This is basically a true statement. Solid state devices do tend to act up with increased temperature but is only part of the truth. They can act up at any temperature also, maybe to a lesser degree but never the less a definite consideration.

Something hot is only relative. If it is hot to your hand you would say it is hot, say 115*. But if is at ambient temperature like 70*, you might not think it is hot. But if the car is outside at 35* and it is moved into a garage at 75* that would be a temperature differential of 40*. One could say it is hot at 75* relative to 35*.

All I am saying is that weird electrical problems can happen at any temperature.

Zralou

Yes I understand that and like I said, I will replace the ICM eventually, but I don't think it is the main problem I have, on friday I started the car and let it sit for 25-30 minutes idling and occasional rev-up without it missing a beat, then the day after it won't start all day.

I'm pretty sure I have a wire somewhere around the coil / ICM area that is breaking down, for it to be so intermittent leads me to believe its not a component.

Sara Lou

Zralou

Well, back to square one again.
I went out this afternoon to see if it was still willing to start after yesterdays success of disturbing the coil lead and getting the car to start, haha too much to ask, back to a no-start condition.
Tried all the old solutions, jiggling wires around coil, ICM, etc, pull connectors off tug wires make sure they're not loose, nothing, same no-start.

This is getting so tiresome, I used to love vettes, but this POS is killing that love. It's going to be weekend again before I can play around with it now, i've already wasted two weekends on this thing when I should be working on the new house.

Anyone have any simple tests I could try to pinpoint this problem?. I'm trying to get a FSM, but it may take a few days to get one. I'm going to run through the diagnostics in the link that Rodj posted, but that will be over the weekend.

If I don't get anywhere, i'm going to pull the coil and ICM off my firebird and try them on the vette (the firebird has a new MSD coil, never been fired yet).

Sara Lou

Zralou

Well, I finally bit the bullet and bought a new ICM and coil. Installed them and had the same 'no-start'.
I then "flashed" the codes with the paperclip, and it fired right up afterwards. Tried it again afterwards, and back to a no-start.

Anyone got a "cheap" FSM?. I believe there are two books for the '93, which one do I need?, or do I need both of them?. I don't intend keeping this vette, soon as I fix this problem its being traded in on a C5, so I only need the FSM that will cover this immediate problem.

Sara Lou

93Rubie

Dumb question, you never stated how you KNOW you are loosing spark during cranking? Just trying to cover the basics.

The short Opti-Spark harness has given issues for some folks. The one that has a connector underneath the pass. side fuel injector cover.

Opti-Spark gives signals to ECM, ECM tells ICM when to fire the coil, ICM fires coil, coil spark to distributor to wires to plugs.

Do you have anyway of verifying Low Resolution and High Resolution signals to ECM from Opti-Spark? Ie. Scan tool?



FYI, C5's have there own issues, just like C4's, but different. There is no perfect car. C5's are quite a bit younger than the C4's too. Age has a factor.

ANY modern fuel injected computer controlled car is going to require good service manual, proper tools, knowledge, if you are going to work on them yourself. This is NOT the age of points/condensers/carburetors. Not trying to be a Butt hole, just a reality check.

Zralou

I stuck a spark plug in one of the plug wires and don't have a spark during the 'no-start' time.
I have good fuel pressure at the rail valve.

I understand what you are saying, but i'm not completely novice, I also own a '94 firebird with the same motor as the vette, and I just changed out the heads, installed roller rockers, all new MSD ignition (opti, coil, wires, etc), and currently working on headers on that car.

I do have scanning software (datamaster) and laptop, but it has been intermitent at best. I suspect the data cable is at fault and ordered a new one last night, so that should help.
The problem lies in, when it starts, it runs good and doesn't give problems, and when it 'no-starts' the scanning isn't going to give much info on just cranking the car.

Sara Lou

caddyboy84

Any kind of security system in that car? VATS perhaps? I'm not too familiar with that year, just a thought since you have no spark at no-start. I had an after-market alarm under my dash that was wired into the tansmission O/D that my alarm guy removed, tranny shifted properly on the H/W after that, HEY ya never know

Zralou

I'm kinda thinking along the same lines myself. Not sure about vettes, but I know my firebird has VATS, and it can be a pain at times.

The car came with two keys, previous owner said one was getting wore out, but both keys do the same, both will start it when it decides to start, and both will be in use during the no-start.

The PO also installed a DVD/radio and there is a mess of wires running around the perimeter of the engine bay, one goes to the pass side fuse box, another one disappears down the pass side under the engine (i'm guessing to the trans or parking brake to prevent using the screen while driving). Why they run all the way round the engine bay i've no idea, that'll be a whole new headache eventually.

The thing that I keep puzzling about is, after installing the new ICM/Coil, it still would not start, but after 'flashing' the codes, it fired right up?. This has been a feature of the car, sometimes flashing the codes will enable the car to start?, maybe ECM?.

Sara Lou

93Rubie

No problem, with the differing levels of experience here I try to error on the side of inexperience. Since by and large many seem to not have much working on these cars.

I think using the scanner to view live engine data during this time may help. Specifically two things. Low Resolution signal to ECM from Opti-Spark and the High Resolution signal as well. If you don't have signal from the Opti-Spark well this could be an issue.

Also, if you have the FSM, you can use a mutli-meter to check for varies voltages/grounds,etc...at connector pins pertaining to the ignition system during this no spark/no start time. If you don't have a FSM, I do suggest if you want to work on this car you invest in one. Save the Haynes manual for spare toilet paper better yet for spare paper for the bird cage.

Finally, VATS disables the fuel NOT the spark. So if fuel pressure is ok VATS should not be an issue. IF VATS is an issue on later cars the security light will be the telltale sign.

caddyboy84

Sounds like someone might have possibly "tapped into" the wrong wire hooking that stuff up. If there is an amplifier wire hooked-up to the battery, try taking it off and pull the radio fuse. See if that helps anything, sound systems and any electronic add-ons sometimes seem to cause problems if they're not done properly. Based on what you're saying, that seems to be the case.

bjm206

The next time you have a no start condition verify that you have 12V (ignition on) at the ignition feed and that the Distr. Ref. Low is a good ground (see borrowed image above). Next crank the engine and see if the high and low resolution pulses are present and consistent. This is hard to do without an oscilloscope but if you turn the engine over slowly with a socket on the balancer bolt you should be able to see if the pulses are present even with a cheap digital voltmeter. If all of the optispark signals are present all the way up to the ECM then it (opti) is very likely not your problem.

The link below will give you a good idea of what the signals should look like (see section on optical disk)

http://www.chevythunder.com/lt1_electrical_page.htm

If all of the optispark signals are there then you need to look at the ignition control signal on the ECM. This signal is generated by the ECM and commands the ICM to fire the coil. This signal will only be generated when the engine is spinning fast enough to start but if it is there (all the way to the ICM) then the coil should be firing. If it is present then you need to check the ICM/coil wiring which are prone to damage.

Zralou

Thanks for all the great replies guys.

It's looking more and more like an ECM problem, I went down to the workshop this morning to drag the ride mower out.
While I was there, I tried cranking the vette, as usual, no start. Just for the h*ll of it, I flashed the codes with the paperclip, and bang!, cranked right up? .

I didn't touch anything, didn't even raise the hood, just tried to start it, no-start, so without moving from where I sat, I grabbed the paperclip and flashed the codes (no codes present because i'd disconnected the battery since the last start). After removing the paperclip I tried starting it, fired right up, turned it off, started it again no problem.

I'm hoping the new data cable arrives tomorrow so I can at least see what's going on somewhat.

Sara Lou

Zralou

Dragging this thread out of the bowels......

Think i've fixed the problem finally. Will know for sure next weekend. Watch this space!!!.

Sara Lou

superjet701k

Just a quick question is your car a convertible, my 96 is and twice I've had no start no crank both times I unlocked put top down an car will start then put top back on and it's fine. Somewhere I have a safety switch not making good contact.

shakedown067

Been working on the same issue with my 96 since august. It looks like I've tracked it down to the opti, but still not sure my self. I had other electrical issues going on at the same time and thought they were related, but now it doesn't look like it. I won't find out till next week at the earliest, as I have no time to work on the car. Subscribed to see how yours turns out.