Need help fuel problem, maybe??
Thread Starter
Intermediate
Joined: Dec 2011
Posts: 33
Likes: 0
From: Greenville Nc
Need help fuel problem, maybe??
I'm having a issue with my 95 lt1, it will crank but won't start. After looking at the service manual, I started troubleshooting the fuel system. Based on the manual's steps I tested the injectors, I tested them on the wrong setting(at the time I didn't realize) and ended up buying a new set. While I waited for the set, I checked the fuel pressure which would be at about 40.5 or 41 psi after I turn the key to the on position. However it would slowly drop, the diagnostic flow chart goes to two problems in the end. One stating that it's a faulty fuel pressure regulator, if I clamp the pressure return line and the pressure holds. The other stating that if the pressure doesn't hold i should look for a leaking injector. After checking a few times, the pressure isn't holding leading me towards the second solution. However these are new injectors and it still won't start. Should my next test be the opti spark? Is there a easier way to test it without removing everything down to the water pump? Any advice would be appreciated, thanks in advance...
Advanced
Joined: Aug 2016
Posts: 55
Likes: 10
From: Plover WI
Check the temp sensor in the water pump. 94-95 LT1 cars are really sensitive to this bloody thing (ask me how I know), and if its failing, cold starts will be near impossible. Unplugging it can help, but not always.
Basically, it freaks out the ECM and keeps trying to switch maps while starting, resulting in a no start, or hard start.
Otherwise, Opti would be another shot. If the signal is bad, it will put the ECM into a fault mode and will refuse to start. It shuts off the injectors. Easy to test, see if it fires on starting fluid.
Basically, it freaks out the ECM and keeps trying to switch maps while starting, resulting in a no start, or hard start.
Otherwise, Opti would be another shot. If the signal is bad, it will put the ECM into a fault mode and will refuse to start. It shuts off the injectors. Easy to test, see if it fires on starting fluid.
Thread Starter
Intermediate
Joined: Dec 2011
Posts: 33
Likes: 0
From: Greenville Nc
Thread Starter
Intermediate
Joined: Dec 2011
Posts: 33
Likes: 0
From: Greenville Nc
Check the temp sensor in the water pump. 94-95 LT1 cars are really sensitive to this bloody thing (ask me how I know), and if its failing, cold starts will be near impossible. Unplugging it can help, but not always. Basically, it freaks out the ECM and keeps trying to switch maps while starting, resulting in a no start, or hard start. Otherwise, Opti would be another shot. If the signal is bad, it will put the ECM into a fault mode and will refuse to start. It shuts off the injectors. Easy to test, see if it fires on starting fluid.
Instructor
Joined: Jul 2016
Posts: 222
Likes: 11
From: Plymouth MI
Sounds like you got fuel pressure, but a slow leak-down when off isn't going to create a no start. It may crank a few more times as it pumps up but it should still start if you're hitting 40 PSI.
If you have oil leaks in the opti area its possible the connections that plug into the opti have become oil coated and no longer making contact. That's the main reason people have issues with the opti, as the cap and optical sensor are usually pretty tuff in a vented application.
If you have a non-vented distributor, they were known to collect slag from the arcing spark and that would damage the optic wheel which many call a "pickup", "cam sensor", or "Hall switch". Not only is spark controlled by the relation of this sensor, but fuel as well. So in other words, be sure the connections at the opti are not oil soaked.
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Thread Starter
Intermediate
Joined: Dec 2011
Posts: 33
Likes: 0
From: Greenville Nc
Just an update...
Been a little distracted with work, but I managed to do a few tests over the past few weekends. One was testing for spark at the coil...I did this a number of times, just to assure myself that I didn't botch the test. Got no blue light or spark when trying to crank it, in complete darkness. Next I tried the wires connected to the icm with a piercing wire probe. I read somewhere in the forum, that the coil and icm work together and are best replaced together. So I purchased replacements for both and threw them in last weekend..... still got no start, but it sounds slightly different.
So today, in preparation for working on it this weekend. I tried starting it up again, to figure out how to describe it. At first listen it sounds really sluggish. I waited a few minutes and turned the key to the on position, not trying to start the car again. And it seemed like the fuel pump is starting up, but slower than usual. So I tested the fuel pressure again and it went up to 41 on key turn, then dropped down within seconds... now I'm confused again about what's wrong with it....
Been a little distracted with work, but I managed to do a few tests over the past few weekends. One was testing for spark at the coil...I did this a number of times, just to assure myself that I didn't botch the test. Got no blue light or spark when trying to crank it, in complete darkness. Next I tried the wires connected to the icm with a piercing wire probe. I read somewhere in the forum, that the coil and icm work together and are best replaced together. So I purchased replacements for both and threw them in last weekend..... still got no start, but it sounds slightly different.
So today, in preparation for working on it this weekend. I tried starting it up again, to figure out how to describe it. At first listen it sounds really sluggish. I waited a few minutes and turned the key to the on position, not trying to start the car again. And it seemed like the fuel pump is starting up, but slower than usual. So I tested the fuel pressure again and it went up to 41 on key turn, then dropped down within seconds... now I'm confused again about what's wrong with it....
Racer
Joined: Dec 2010
Posts: 428
Likes: 125
There is a check valve in the fuel pump that is probably leaking down, but that wouldn't result in no-start, just slow start. No sparks is your issue. Probably that damn optispark. I've heard aftermarket ones are junk, but I also don't think OEM is available anymore.
Melting Slicks
Joined: Jul 2005
Posts: 2,649
Likes: 863
Even if you have a gradual drop in fuel pressure with the pump off - that probably won't prevent the car from running well at idle or under anything but heavy load. As long as the fuel pump can keep the fuel rail pressure at around 42 ish psi - everything will be good.
First thing - hook up the fuel pressure gage and start her up - is the pressure while it's running @ 42. If so - you need to look elsewhere. IF replacing the coil and coil driver didn't fix the problem - either you got defective parts (it has happened to other forum members), or you have an opti problem. Is the Check engine light on ??? (The check engine light will go on if either the Hi res opti output or the low res output is lost, but the other one is present. If you lose both - no CEL.
First thing - hook up the fuel pressure gage and start her up - is the pressure while it's running @ 42. If so - you need to look elsewhere. IF replacing the coil and coil driver didn't fix the problem - either you got defective parts (it has happened to other forum members), or you have an opti problem. Is the Check engine light on ??? (The check engine light will go on if either the Hi res opti output or the low res output is lost, but the other one is present. If you lose both - no CEL.
