Need some C4 wisdom...
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Joined: Sep 2011
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From: Woodbury MN
Need some C4 wisdom...
I have an '85 coupe. It has the stock 350 with a 4+3 trans and 99,000 miles on it. In the last 6 weeks I have put rebuilt Bosch injectors in, new fuel pressure regulator, EGR control valve relay solenoid, new gas filter, plugs, and a new idle air control pump or valve. I took the car 2,270 miles last week from St.Paul to Colorado Springs and back. It ran pretty good at 75mph and the air on most of the time and averaged 27 mpg. The problem is that when I try to start it when it is warm it cranks over and over and over for a long time before it even things of firing. Sometimes I have to turn the key off then hold the pedal to the floor then start it that way. When it does start it acts like it's flooded and it puffs out the exhaust until it clears out. I have wondered about timing but I don't imagine that it has changed since before the work done when it started pretty good warm. I would appreciate any wisdom from y'all. Thanks, Jay
Le Mans Master
Joined: Mar 2004
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From: Dublin CA
Start by testing the fuel pressure. Hook up the gauge and turn the key on, pressure should almost immediately build to about 36-39 PSI and hold.
A bad injector or fuel pump will cause the pressure to quickly fall. Get back to us with what you find.
A bad injector or fuel pump will cause the pressure to quickly fall. Get back to us with what you find.
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When the throttle is held wide open during the start cycle, the ECM goes into "flooded mode". It turns OFF the injectors to help clear the cylinders. That should explain your success with starting on a wide open throttle.
Need to check the FP as everyone above has suggested.
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Need to check the FP as everyone above has suggested.
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Last edited by JrRifleCoach; Jul 1, 2012 at 01:14 AM.
Thread Starter
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Joined: Sep 2011
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From: Woodbury MN
Hard starting
Hi John, I talked to the shop that did the work on my car and the mechanic told me the fuel pressure built up and stayed there. When the injectors were changed the cold start injector wasn't. Looking on ebay the cold start injectors run about $150 but the cold start injector sensor is around $30. I would probably start with the sensor and see if that works. I don't have a fuel pressure gauge but if I get one where would I hook it up to do my own test? one more note... it used to start right up when cold. Now it turns over for a long time weather cold or hot.
Any thoughts would be appreciated. Thanks, Jay
Any thoughts would be appreciated. Thanks, Jay
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Joined: Jun 1999
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From: Merritt Ils Fl
Most chain parts houses have fuel pressure gauges they will loan at no cost. Look on the passenger side of the fuel rail, you will see what looks like a tire valve, should have a screw on cap. That is where fuel pressures are measured.
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Joined: Sep 2011
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From: Woodbury MN
Problem resolved
So today I went to Autozone by my place and got a fuel pressure gauge on loan. When I screwed on the fitting on the fuel rail I tightened it with a pliers. When I tested the pressure with the key on it only registered about 10 pounds. The same when it was running. So in a phone conversation with John and Cole at Fuel Injector Connection where I bought my injectors they helped me understand that the fuel pump was probably the culprit. So I went to NAPA and got a Carter fuel pump and screen. I was surprised how easy it was to change. When I put the gauge on again with the new pump it said the same 10 pounds. Then the mechanic from next door came over and loosened the fitting on the fuel pressure gauge and it went up to 40 and held there. Then he wondered what the pressure was really like with the old fuel pump. I hated to think I just spent the money on a new pump if I didn't need one. The bottom line is that the car starts right up when hot and it didn't do that with the old pump so I'm happy. Now I can start to think about spending my overtime money on fun stuff, not fixing problems. Thanks to everyone who pointed me in the right direction. Jay
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A bad regulator diaphragm will cause this too.
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From: Woodbury MN
Hi John, I have another question about my '85. This is a problem I thought I had solved by putting a new fuel pump in. My car doesn't start for a long time either hot or cold. It cranks and cranks but doesn't fire for 10 to 15 seconds. I can't figure out what's going on. It acts like it isn't getting any gas. Here is a list of parts that have been replaced in the last 6 weeks; Fuel injectors, fuel filter, fuel pressure regulator, fuel pump, plugs, alternator, idle air control valve, EGR control valve relay solenoid, and this is my second tank of premium gas. I used to use regular. Can you think of any other reason the car won't start well? If I hold the peddle to the floor then turn the key it starts but runs loaded up for a few seconds. Any thoughts would be appreciated. Thanks, Jay
Burning Brakes
Joined: May 2011
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From: Louisville Ky
if you hear the pump run for the 2 secs prime when key is turned to run, the pump if operating. I don't believe pump is likely to be part of hard starting issues, normally. over rich, yes. my 91 is sensitive to timng being retarded, causing long crank times.
as you see, it didn't fix the OP problem, either. start a thread describing your problem, year of vette, etc. you can replace a dozen components and still have the problem.
if you think it is too rich, try holding throttle WOT while cranking to see the reaction. that will point you to a solution.
joe
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Took the car to my buddies house and he had a fuel pump ready to install. As soon as he opened the hood, he said the fuel regultor was leaking. $54 later, I have a smooth running Corvette. Amazing what a little item can do for perfomance.