Hard starting LT4
Thread Starter
Instructor
Joined: Jun 2003
Posts: 160
Likes: 2
From: Indiana
Hard starting LT4
In the past 30 days or so my LT4 CE is hard to start on occasion. It will crank for up to 10-15 seconds before it will turn over. Sometimes I stop cranking it, count to 3 and try again. It will start immediately. This doesn't happen every time, but more often than not. When it does happen, I get a strong smell of fuel in the exhaust. Thoughts??
Melting Slicks
Joined: Oct 2004
Posts: 2,510
Likes: 4
From: Austin Texas
Not a lot of info. here, but you may have a leaky injector(s). I would hook up a FP gauge, and check the bleed down rate, It should maintain ~40psi and stay there for quite awhile. A fast reduction in psi could be a leaky injector or a faulty regulator. Use the "search" feature and you can find many related threads on leaky injectors and bad fuel pressure regulators....
Safety Car
Joined: Sep 2006
Posts: 4,129
Likes: 1
From: Pasadena CA
In the past 30 days or so my LT4 CE is hard to start on occasion. It will crank for up to 10-15 seconds before it will turn over. Sometimes I stop cranking it, count to 3 and try again. It will start immediately. This doesn't happen every time, but more often than not. When it does happen, I get a strong smell of fuel in the exhaust. Thoughts??
Did you get a resolution on this? My LT4 has just started doing exactly this. Seems like fuel to me even tho it has a relatively new fuel pump which I can hear
Burning Brakes
Joined: Mar 1999
Posts: 1,150
Likes: 138
From: Raymore Missouri
Guess I'll add myself to the thread. Mine started doing the very same thing, cranks longer than normal but eventually starts. In fact I had it inspected (stupid Missouri MVI 
) and the service manager thought it was a joke. I wish that were the case... 
Edit: Forgot to mention mine has all original components. My first thought was fuel pump, but if you guys have changed yours, it might be something else. /edit
Mike
) and the service manager thought it was a joke. I wish that were the case... Edit: Forgot to mention mine has all original components. My first thought was fuel pump, but if you guys have changed yours, it might be something else. /edit
Mike
Le Mans Master
Joined: Jun 2002
Posts: 6,097
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From: Cincinnati Oh
Race Director
Joined: Dec 2006
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Have you given the fuel pressure regulator's vacuum line the sniff test?
Disconnect it, walk away from the car, sniff for strong gas smell. Of course visible wet gas means the diaphram is blown in the FPR w/o sniffing.
Disconnect it, walk away from the car, sniff for strong gas smell. Of course visible wet gas means the diaphram is blown in the FPR w/o sniffing.
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From: Texas
Le Mans Master
Joined: Jan 2006
Posts: 5,621
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From: Orlando FL
I have been working this problem myself for a while now but does not seem to be as bad as yours. I also just got a PM from someone else with the similar symptoms in regard to the same problem wanting to know if I solved it. Unfortunately I have never found a thing and it all looks good on my engine.
Sometimes it pops right off, or may spin for an extra 3 seconds or so. Just don’t know how deep I want to go on this since it’s a non-issue, but just an annoyance.
Sometimes it pops right off, or may spin for an extra 3 seconds or so. Just don’t know how deep I want to go on this since it’s a non-issue, but just an annoyance.
Thread Starter
Instructor
Joined: Jun 2003
Posts: 160
Likes: 2
From: Indiana
Well, I've been working with Jon from FIC to solve problem. Ordered a set of matched Bosch Gen III injectors for my LT4. Installed them yesterday. They work beautifully, smoothed out the motor, but that wasn't the problem. Fuel pressure goes to "0" immediately after turning off the car. Checked the fuel pressure regulator and don't think that's the problem but will replace anyway because of age. Jon thinks it is the fuel dampening valve in the gas tank. I will have my mechanic do that sometime soon. I am not that comfortable with messing with the gas tank.
Instructor
Joined: Mar 2008
Posts: 111
Likes: 0
From: York PA
Well, I've been working with Jon from FIC to solve problem. Ordered a set of matched Bosch Gen III injectors for my LT4. Installed them yesterday. They work beautifully, smoothed out the motor, but that wasn't the problem. Fuel pressure goes to "0" immediately after turning off the car. Checked the fuel pressure regulator and don't think that's the problem but will replace anyway because of age. Jon thinks it is the fuel dampening valve in the gas tank. I will have my mechanic do that sometime soon. I am not that comfortable with messing with the gas tank.
Thread Starter
Instructor
Joined: Jun 2003
Posts: 160
Likes: 2
From: Indiana
My pump, filter and injectors are now all new. I will be replacing the regulator, but we don't think that is the issue. That only leaves the fuel dampening valve. Maybe I will try to take on that task, but will want to do my research first.
Thread Starter
Instructor
Joined: Jun 2003
Posts: 160
Likes: 2
From: Indiana
Finally got around to pulling the fuel filler door off and doing the "clamp the supply and/or return hoses" to determine the problem. It was not the FPR. It was the fuel dampening valve. Took awhile to get it and a fuel sending unit gasket in to my local dealer. I did the work today. Had to wrestle with the supply hose to get it to budge, but prevailed. Everything went easily thereafter until I got to replacing the fuel strainer. This was my first time messing with a fuel pump and/or strainer so I had no experience. When I removed the strainer it pulled off of the flange and left the collar in place. I didn't realize the collar should come off as well. When I went to the parts store to get a new strainer it didn't look like what I removed from the pump. Took me a bit to figure out what I had done!! That kind of detail is not included in any articles I read or the GM service manual. Oh well, that's what makes doing your own wrenching so fun. Anyhow, the new valve is in place and working beautifully. Thanks to Jon from FIC for his help walking me through the diagnostic. Go USA!!
Go USA!!
Instructor
Joined: Jun 2003
Posts: 158
Likes: 0
From: Somewheres in FL
I have the same problem on my LT4. Initial cold starting is hard til the fuel gets there........then runs fine. restart is much easier, if not almost normal.
So, I should check the fuel pressure regulator first, then the fuel dispensing valve.............anything else prior to the fuel dispensing valve?........looks like a project to get to it.
So, I should check the fuel pressure regulator first, then the fuel dispensing valve.............anything else prior to the fuel dispensing valve?........looks like a project to get to it.
Last edited by bgrant_12002; Aug 10, 2008 at 10:45 AM.
Instructor
Joined: Jun 2003
Posts: 158
Likes: 0
From: Somewheres in FL
I replaced the fuel pressure regulator, after it failed the sniff test. Pulled the pulsation damper and bypassed it today. Still having same problem. Cold start has fuel pressure low. Have to pump the pedal to get the 1996 LT4 started. Runs fine after that. Something is slowly letting the pressure bleed off. Is the next step to replace the Fuel pump--does it have a backflow valve in it as well??
Last edited by bgrant_12002; Aug 13, 2008 at 03:29 PM. Reason: update
Burning Brakes
Joined: Mar 1999
Posts: 1,150
Likes: 138
From: Raymore Missouri
Anyone gotten this problem totally fixed? I have not had time to mess with mine, but I wondered if anyone had found a resolution. I guess I need to find some time to start taking it apart.
Thanks,
Mike
Thanks,
Mike
