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Discussion Starter #1
Recently purchased a 95 Z-28 with a new Gm crate motor and less then 1500 miles on it. Beautiful convertible and love the car, however I drove it home which was over 400 miles one way and it ran great and no issues. However in the last cpl of days I have driven it and it has been running great until I get to a stop light and it will die. It will not start again until after sitting for like 5 mins and then starts right up. Today it did this to me at a stoplight and I waited in the lane with flashers on and it started only to get me to the next stoplight and did it again. Was able to coast into a parking lot and sat and waited and it started right up and I drove it for about 30 mins with no more issues. This car has a new fuel pump and fuel line on it and at times I smell raw gas but unable to find a leak anywhere and may not even have anything to do with this problem. Any one have any ideas on where to start or what this might be? I will note that when driving home it was night and cool out and the times this has happened it has been during the day and temps are warmer. Today it is 80 when this happend! So again not sure even if that has anything to do with it. Thanks!
 

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a common problem is the optispark distributor it sits in front of the engine the lt1 is very different from any other v8 . im not saying for sure but they are known to be problematic .
 

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Discussion Starter #4
went a pulled paperwork for car and optispark was purchased new with the motor in April of this year. Could this be faulty??
 

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I have seen new parts go bad . Anythings possible ? And it is a common problem if it ends up being the problem they do make an upgraded model check summit .
 

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Tested distributor and it is not it as I agree swede1969 I have purchased many new parts to have them be junk. Called the previous owner and it seems that he had this problem when putting in the fuel pumps. With the last pump he drove the car for about 250 miles and did not have an issue so figured problem was resolved. THinking it may be a relay problem as it is not the fuse for the pump as I have checked that. Had it in the shop this morning and can not find a leak anywhere in regards to fuel and did figure out the fuel smell is coming from under the hood and not towards the back of the car as I had previously assumed. So going to check fuel pressure and check regulator. If that checks then thinking it may be a relay somewhere between pump and motor that may get hot and shut down and then when cool again lets the car start. so let the search begin. Thanks swede1969! Please if you have other ideas I would love the hear them!
 

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If you suspect the relay is "bad" - just pull it and jumper connections #30 and #87 on the block and see if fuel pump now runs correctly.

I doubt it's a relay, but who knows ...

Have you checked/changed the fuel filter?
Have you hooked up a fuel pressure gauge and monitored pressures when it has 'no start' problem?

Is this a stick or auto?
 

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Discussion Starter #8
checked fuel pressure it is at 38-43 as it needs to be. remove vacuum line and pressure shoots up 5 lbs as it should. However at the tip of the key pressure moves VERY slowly and am not sure if that is correct. Have not checked fuel pressure when it won't start as the times it has done this I have been in the middle of traffic so not very feasible at that time and of course while in the shop it runs awesome. Fuel filter is new and car is an auto.
 

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Pressure should be retained with key off, and should rise quickly once key is turned to 'on/start' the first time.

Could be weak pump ... do you know brand and history?
Constant operation with low fuel levels in tank are killers on these vehicles. Pump runs 'hot' and breaks syphon often.
 

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Discussion Starter #10
fuel pump is oem as the previous pump put in was not so previous owner went back to oem and as stated drove the car for like 250 miles with no issue. Fuel pump has like 600 miles on it. Couple things I have noticed are : 1. when filling the car with fuel fuel gauge does not read full but between 3/4 and full somakes me waonder if that sensor in pump is off and 2. it keeps coming to mind that the times it has stalled it has been hot out and was hot when it did this to the previous owner. I am not sure if this honestly has anything to do with it but it just seems weird that it ran fine the 400 miles home at night with no issues at all. Car now shows between 1\4 and half full and have driven it to shop and home several times( this is about 20 blocks away) with no issues even sitting at a stop light waiting it has ran fine. Temp is 73 degrees and not baking hot. So going to fill tank again and see what happens. May stick fuel pressure regulator on it and timing light and drive it and see if it will die and what diagnostics will show with the gauges.
 

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Discussion Starter #12
Well I am hoping to figure out this issue as this is such a beautiful car! The previous owner has almost 8k in this car with new paint, motor, fuel pump and lines, tires and the list goes on and I have the receipts for it all. THis is pretty much a brand new car with just a small hiccup. I keep hearing that this is a common issue esp with the 95 but have yet to find the "fix." I am just hoping hubby doesn't say enough and time to move it on and get something that we can depend on as right now scared to drive it too far and that is not what I got this car for. I want to cruise in this baby!
 

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If your present checking of the fuel pressure and other obvious electrical doesn't pay off, you might want to Ohm each of the injectors - I've had two intermittent (and one just died ...) vehicles that turned out to be an injector going bad.
That particular injector was very low impedance and I suspect it would vary enough with heat that it in effect caused a 'short' or draw that was pulling the ECM to ground (shutting down injector circuits) periodically.
Finding the failing injector and replacing them has effectively fixed all of these vehicles and stopped them from stalling when warmed.
Long shot, but something to check ...
 

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Discussion Starter #14
Worth a shot and willing to try whatever at this point to keep her running. Will be my next step tomorrow. Thank you for EVERYONES input! I so appreciate it!
 

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Here is something I wanted to throw out there. I stopped by our local auto zone on my way back from shop. Had a guy wait for me to park and came right up to my car commenting on how beautiful he thought it was. Stated he had one pretty much like it he bought brand new and same year but sold it about 4 years ago. So I asked him about the issue I am having and he stated his did the same thing and after replacing opti, fuel pump, coils and the like he found out it was his VATS security system. Said he bypassed that and had no problems again. Was curious if any of you had heard of it going bad? I did some research and there seems to be at times some issues so was curious how common this problem might be. Called my Chevy dealer for a quote to possibly fix it if that was the problem and about fell over when they told me anywhere from 2-3k. Needless to say I think if that was the issue it would be the red hot rod's demise and will be parked with a for sale sign in it.
 

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I bought a 96 Z28 convertible brand new and the VATS started acting up within 2 years of me having the car. Sometimes it would start and sometimes not. It was under warranty and my neighbor (whom I bought the car through - I got his discount) was a GM mechanic so he diagnosed it and fixed it right (bad module or something like that). Never had a problem after that.

I traded it in on a 2002 Z28 as that was the last year for the F-body and I wanted a bookend to my 67. I still miss that car...
 

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'Normally' ... A bad VATs system will cause starting issues vs. running issue. Not to say that the system couldn't/wouldn't cause an issue, with lack of fuel flow/pressure you're seeing, ... I've just not run into that yet.

There are plenty of threads and info on bypassing the system to prevent the no-start problem, but not sure if the same 'fixes' would address something happening once the system has said 'okay, sure' to the fuel system.
Again, bypassing the relay via jumper, or using a indicator light to monitor relay coil power, would be a quick check to see if it was dropping out during run conditions.

I've used a relay bypass to track down more than one problem on a modern system.
 

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Interesting suggestion of VATS affecting performance rather than starting issues as John suggests. Seems like it would be black/white, not gray.

Usual VATS troubleshooting, doesn't start, as in no starter motor working, remove key, wait min 3 minutes, then try again with same key, engine will start and run until turned off. Then cycles through again.

If jumper across fuel pump relay socket makes it work, then replace relay as it may have some carbon build-up across contacts creating a high resistance as this effect would reduce power to fuel pump.

A good troubleshooting tool is a test light with long leads,such as an older tail light socket, single filament, 1156 type. This way you can view the light, or loss of light inside the car while driving, of any circuit of your choice. Find a good ground inside, and alligator clip the remaining lead to chosen circuit and watch.
Seeing a light is better than reading a meter.
 

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Discussion Starter #20
Well it wasn't the vats. It was the ICM. Put a few washers on to keep it not so close to the head and it has driven beautifully! Took it today out and about most of the day with in town driving at 90+ degrees and no issues! Not sure if the problem is fixed so will continue to update. Thank you so much to EVERYONE for their input I so appreciate it and I have learned a ton already! Thanks again!
 
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