1999 GP 3800SC into 1986 GT. cars has been swapped for few years. turn on the key, fuel pump runs a few seconds crank it over, Won"t start. If I crank it "continuously" for about 10-15 seconds, the oil pressure builds and it starts up and runs fine. Both my other swaps(3800Sc) start right up with just a turn of the key IMMEDIATELY. WHY does this one have to "Crank" for so long before starting ?? HAS new fuel pump Relay AND oil Pressure sender. fuel pressure 55 PSI. Thanks
Does the fuel pressure come up and stay there? Or does it drop back off until cranked again. Most swaps on 3800 bypass the oil sending unit and run the fuel pump relay directly off the PCM. This way, fuel pump is turned back on as soon as the PCM sees ignition pulses. If the pressure is going back down it could be a leaky injector or most likely a leaking pressure regulator. When the regulator leaks the fuel can come out the vacuum fitting, loading up the intake with fuel causing a flooded condition causing long cranking time. Pull off the vacuum hose after pressure had came up and see if there is any fuel in it. If so it is bad. And if it is using the original wiring to the fuel pump, cranking time can be extended further due to pressure not coming back up until the sending unit turns the pump back on. Another possibility but rare is a weak crank or cam signal. Being both are hall effect switches on 3800s and not signal generators, like a pick up coil on a 2.8, they normally just fail.
I was wondering about the regulator, because before I replaced the oil sender, the fuel pump ran "full time" with the engine Off, and I could actually HEAR the fuel running through the lines, sounded like the fuel was running in a loop non stop ! Will a bad regulator let the pump pick up the fuel, send it through the lines and put it back in the tank" Non Stop" ??? that what it sounded like. I'll have to put the gauge back on to see if it does hold pressure after the 3 second run. Thanks
OK first let me try to give you a general idea how that regulator works. Hang with me here. It might sound stupid, but you will get the picture. If you take a Bic pen, take the stuff out of it until all you have is the tube. Then take that tube and put one end on something very flat. Try blowing through the other end. The pressure just builds up. Now on the other side of the flat object you put a spring. Now when you blow through it nothing comes out until you overcome the spring tension. That gives a "regulated" pressure. But we have to put another bone in there. You want the pressure at one area unless you are hammering on the gas and then you want a little more. So, you put a rubber diaphram on that flat object, enclose it in a air tight housing and at on end of the housing you put a vacuum fitting on it. Now when you have high vacuum (idle) some of the spring tension is taken off the flat part and the pressure is lower. Soon as you hammer the throttle, the vacuum drops, slamming the the full tension of the spring onto that flat piece, raising the pressure. So now that you have a idea what is really going on in it you can visually understand how they can fail. Remember that diaphram? Well that is the most common failure. It will get little cracks around it. Causing full pressure all the time and at the same time fuel is sucked into the vacuum line. The spring is still against the flat part. Then the second failure. That area between the tube and the flat part. A piece of debris(dirt, rubber from hose) gets stuck between the tube and the flat part and causes the pressure to drop back down and a lot of fuel is returned right back to the tank. That is one of the reasons I recommend filters so often.
That brings me to something else. On older cars with lower pressures. It was not a big deal to run most of the pump load off the oil sending unit. Kind of gives a safety function to stop the pump if the engine dies. But anything that I have worked on with higher pressures uses the relay exclusively, driven by the PCM. If you are using a PCM that normally runs the fuel pump relay, I highly suggest wiring that way. Higher pressures also mean higher loads on that circuit. The relays can normally handle the load better than a sending unit.
[This message has been edited by cmechmann (edited 12-16-2018).]
so, at idle, or with the key just turned on,motor not running the regulator is letting more fuel go through and back to the tank, right ? because what this sounds like is if there's a line from the tank, through the injector lines and straight back to the tank, sounds like there nothing even slowing the fuel Flow down . Reg totally shot ? I'm going to take a old one I have and take it apart. then I'll know exactly what I'm dealing with. Thanks
Lou, I think you may be chasing the wrong animal here. I posted in another of your threads on this subject. The Relay get's a 3 second turn on from the ECM to prime the engine, and then the ECM turns the relay off until it gets enough pulses from the Crank Position Sensor telling the ECM that the engine has started running. At that point, it turns the relay back on until such time as it sees no more pulses, or the ignition is turned off. The Oil Pressure sensor is a back up to the relay. It sounds like your ECM is not getting the required signal to re-energize the relay, but the Oil Pressure sensor is getting enough PSI through the cranking process to close the switch and allow power to the pump directly, thus after some cranking the engine starts and runs.
I would focus on this signal, since it seems like it is not present based on your other posts. I no longer have my wire diagrams, so I can't help you trace it, but it's there.
If you are seeing 55 psi at your regulator, it sounds like it is OK. You can test it by seeing if the pressure bleeds off quickly. If it does, it still could be a stuck injector, so then you clamp off the return line, and re-test. You should see more like 70 psi on this test ( confirming that the pump is strong), and no bleed down if the regulator is bad ( It's bad in this case only if you had rapid bleed down earlier. This is also the test for a good pump). If it bleeds down with the hose clamped, then you have a leaking injector.
WHERE IT IS now. turn the key ON, has 50psi "non running". Does Not "bleed down". Crank it until oil pressure is 20 pounds "non running yet", and then it starts with the oil pressure up. still holding 50 PSI Fuel and 60 PSI oil pressure . Shut it off, and it will still be holding 50 PSI fuel pressure after 20 minutes, does not bleed down, (not even 1 psi). For some reason, it has to have Oil Pressure Before it will Start ! checked the" ign switch" and thats OK. I thought "Maybe" the switch was not giving spark "While cranking", but it IS.
What goes back to the tank is the fuel that is not used while keeping the pressure up. Different loads will change the amount going back to the take. Even at full load some of the fuel is going to go back to the tank. But something does not make sense here. You pressure readings are near normal. You should get about a 5 lb drop when vacuum is at the regulator. Even with that. You have plenty of pressure to get it started. If you have standing pressure of longer than 20 mins, I doubt you have a fuel delivery issue. You may be chasing a ghost at looking at the oil pressure. Is this something that just started happening? Or is this something that has always been an issue with this car? Are you sure it runs fine after started? Doesn't act like it is loaded up with fuel?
Just a shot in the dark here. The ignition module should have it's own 12v feed from the ignition switch and should be full 12v anytime the key is on. It don't make sense to have it's supply hooked to the sending unit. But I have seen stranger things. On Darbysan's input. The Ignition module sends both the crank shaft and cam shaft reference signals to the PCM. Then the PCM sends a signal back to the module when to fire. PCM uses the cam signal to determine which coil and which injector. The module also has a voltage regulator to supply the cam and crank sensors voltages. That subsystem relies heavily on good grounds.
[This message has been edited by cmechmann (edited 12-17-2018).]
any idea" what color wire" the HOT is supposed to be at the ign module on the 1999 GP 3800 ? (I'll have to look up which it is on the GMTuners chart) so I can check to see if there IS power ANY time the key is on.
I'm watching your other post too. For the Ign. module you should be using the pink or pink/black wire from the C500 connector that originally went the 2.8 coil. Or to the module on a distributorless 2.5. Make sure it is not shared with the injectors. They can pull the voltage down because it is such a long run. If the voltage drops, it may not be getting enough voltage until you let off the starter and momentum of the engine is enough to get it started. The injector 12v feed should come from the C203 inj1 and inj2 circuits. Even if this both are not in the rear side of the C203 connector, there should be both running to the fuse box. I used inj1 for the front bank and inj2 for the rear bank. If i remember I'll kook at my car to see what color the 12v is on the module side of the ignition connector, but I am getting absent minded in my old age. Also a very good wiring reference site http://www.cowspatoot.com/fiero/wiring/http://www.cowspatoot.com/f...nd_Knock_Sensors.gifhttp://www.cowspatoot.com/f...rom%20phonedawgz.jpg The 2 sites that Darbysan posted are very thorough. However on the 3x,18x and cam sensors I would only use a scope or an LED. You can use an LED. A led will draw much less than a noid. On side to ground and the other to the signal return for each. If you don't get a flash the first time, turn it around. And do it at the ICM connector not at the crank cam sensors. Remember the cam signal has to rotate 2 rotations for one flash. And please remove power from the fuel pump while doing ignition checks. You don't want it to fire up while testing. The 3800 ignition after 92 has to be one of the most reliable I have worked on. Of course coils and wires. But most of the rest is very robust. Except for mechanical damage, an occasional cam sensor. Pre 92 had to bad habits. The Motorola coil pack module sucked and they also had a habit of dropping the magnet off the cam gear. It stayed virtually the same from 1992-2005. How was VATS disabled? In the tune or with a signal generator? I'm just knocking down possibilities.
[This message has been edited by cmechmann (edited 12-18-2018).]
May or May Not be related. before "starting" the car, key off, tach at zero. turn key On, tack moves a little. start it up and idles ,tack at about 900prm. But, Rev it, and it will not go above 1000 rpm ! ( like I said, don't know if this has anything to do with starting issue)
Latest, still must Crank till there"s oil pressure, BUT, if Spayed with" starting fluid", it starts IMMEDIATELY ! Why would it Have to Have OIL Pressure ? It Maintains 50 PSI of FUEL Pressure the entire time from as soon as the key is turned on !
