A quick question for the 84 gurus...
Thread Starter
Melting Slicks
Joined: May 2007
Posts: 2,382
Likes: 2
From: Kathleen FL
A quick question for the 84 gurus...
A long time childhood friend of mine finally decided to pick up an 84 for the steal of a lifetime. $3000 got himself a pristine bodied 84 with the Z51 suspension, performance axle, A4, with 51k miles. It has been sitting in a garage for about 5 years collecting dust, so obviously it couldn't be started and had to be trailered back to his house.
Just for luck, we changed all the fluids in it, e.g. oil, trans fluid, coolant, brake fluid, Amazingly it started up as soon as we picked up a battery for it. But here's the issue. We drove it around town for awhile like maybe 2 hours enjoying it and suddenly it shut off on us. We restarted and it restarted just fine, and it kinda idled higher than normal, though smoothly, but will sputter, backfire and stall if we give it any throttle. So basically we had to idle it home back to our street. I was wondering if there was a CEL set but its not on when the problem starts. There were no codes set and it will just do this every time it starts up.
I know this is not the same car in the video, but it does EXACTLY this, even as soon as it starts up, warm or cold:
http://www.youtube.com/watch?v=dxQsPwVznSU
Any help would be perfect!!! Thanks for this forum!
Just for luck, we changed all the fluids in it, e.g. oil, trans fluid, coolant, brake fluid, Amazingly it started up as soon as we picked up a battery for it. But here's the issue. We drove it around town for awhile like maybe 2 hours enjoying it and suddenly it shut off on us. We restarted and it restarted just fine, and it kinda idled higher than normal, though smoothly, but will sputter, backfire and stall if we give it any throttle. So basically we had to idle it home back to our street. I was wondering if there was a CEL set but its not on when the problem starts. There were no codes set and it will just do this every time it starts up.
I know this is not the same car in the video, but it does EXACTLY this, even as soon as it starts up, warm or cold:
http://www.youtube.com/watch?v=dxQsPwVznSU
Any help would be perfect!!! Thanks for this forum!
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
After you check the fuel pressure, the spec is from 9 to 13 psi, start looking for vacuum leaks. It is not uncommon for a vacuum leak to develop between the intake manifold lid and base.
RACE ON!!!
RACE ON!!!
Thread Starter
Melting Slicks
Joined: May 2007
Posts: 2,382
Likes: 2
From: Kathleen FL
Update:
So I checked the spark plugs. The Autolites in it actually don't look bad at all!. I found a couple of receipts in the car and actually the spark plugs and the plug wires were changed in 2001. But the plug wires still look very nice, almost new after I wiped the dust off them!
The fuel filter was replaced in 2003 according to another receipt. Could these things just suddenly go bad after time?
When I was checking the timing, it was over spec at 10 degrees. I put it to 6 degrees and it started to run rougher and had some idle surge. So its back at 10 for the time being.
The vacuum is actually stable on start up. But it goes from 18" at idle to 3" when you blip the throttle. But it will maintain 17-18" at a high idle. Seems to wanna idle at 1200 rpms. Any lower it will run very roughly and stall out. Fuel pressure is 10 psi and dips down to almost nothing when you slightly rev it. Might seem like a combination of things, e.g. fuel pressure regulator, vacuum leaks from somewhere, possibly a leaky fuel system or weak fuel pump, etc.....
So where are the potential places for fuel leaks on the 84s? I did smell some very noxious gas fumes from the engine bay and almost passed out...
So I checked the spark plugs. The Autolites in it actually don't look bad at all!. I found a couple of receipts in the car and actually the spark plugs and the plug wires were changed in 2001. But the plug wires still look very nice, almost new after I wiped the dust off them!
The fuel filter was replaced in 2003 according to another receipt. Could these things just suddenly go bad after time?
When I was checking the timing, it was over spec at 10 degrees. I put it to 6 degrees and it started to run rougher and had some idle surge. So its back at 10 for the time being.
The vacuum is actually stable on start up. But it goes from 18" at idle to 3" when you blip the throttle. But it will maintain 17-18" at a high idle. Seems to wanna idle at 1200 rpms. Any lower it will run very roughly and stall out. Fuel pressure is 10 psi and dips down to almost nothing when you slightly rev it. Might seem like a combination of things, e.g. fuel pressure regulator, vacuum leaks from somewhere, possibly a leaky fuel system or weak fuel pump, etc.....
So where are the potential places for fuel leaks on the 84s? I did smell some very noxious gas fumes from the engine bay and almost passed out...
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Michael S. Palmer
Team Owner
Joined: Aug 2000
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From: San Pedro CA
after sitting for 5 years, it's anyones guess.
the fuel filter could get clogged that quickly buy the goo that has built up in the tank. I would replace the filter, but also, as CFI said, drain the tank...get that crap out.
It could be the FPR... no question... or a bad vacuum hose. I would take some carb cleaner and start hitting the various things on the intake, if the idle picks up and it starts to run better, you have just found it.
I would first drain the tank...
the fuel filter could get clogged that quickly buy the goo that has built up in the tank. I would replace the filter, but also, as CFI said, drain the tank...get that crap out.
It could be the FPR... no question... or a bad vacuum hose. I would take some carb cleaner and start hitting the various things on the intake, if the idle picks up and it starts to run better, you have just found it.
I would first drain the tank...
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
The right front TB has a fuel accumulator in it, with a diaphragm. The left rear TB has the fuel pressure regulator, of course, with a diaphragm in it, also. Those are the only two, exclusive to the Crossfire, potential leak points that come to mind. Like all of the C4s there is a section of fuel hose, both supply and return, under the hood to accommodate engine movement. The steel fuel line tubing seems pretty bullet proof. You can check for lose fittings, but in light of all the extended sitting, I would start looking at (sniffing) the TBS at the diaphragms I spoke of.
RACE ON!!!
RACE ON!!!
Thread Starter
Melting Slicks
Joined: May 2007
Posts: 2,382
Likes: 2
From: Kathleen FL
I'm assuming that both diaphrams should not squirt any fuel at all before start up when fuel pump is primed. Pressure builds to 9-10 psi but is all lost in 1 minute. Looks like the diaphrams might be bleeding out some fuel pressure and leaking out elsewhere.
Thread Starter
Melting Slicks
Joined: May 2007
Posts: 2,382
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From: Kathleen FL
I'm pretty sure there is no backpressure because the main cat was replaced with a big 3" pipe, and the mufflers were cut and elims where put on. Plus we were driving the car for about 2 hours before the car started acting up.
Instructor
Joined: Jul 2007
Posts: 229
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From: FT Lauterdale Florida
ive heard about spraying carb and choke cleaner around areas you think have vaccume leaks? the idea is the engine will stumble when you spray it in a vaccume leak because choke cleaner is not flamable?
id check manaflod top plate all the way around, as well as all other things up on the manafold.
also I want to know ( for my self as well ) how to go about hooking up a fuel preassure guage, and possibly being able to "bench flow" the fuel pump in the tank, by un hooking a fuel line up by the engine, and re routing some rubber fuel hose back to ? a 5 gallon gas tank or something? see how much fuel is pumping out, like how many gallons per minute / or half minute, maby able to eliminate or varify faulty or dead fuel pump
id check manaflod top plate all the way around, as well as all other things up on the manafold.
also I want to know ( for my self as well ) how to go about hooking up a fuel preassure guage, and possibly being able to "bench flow" the fuel pump in the tank, by un hooking a fuel line up by the engine, and re routing some rubber fuel hose back to ? a 5 gallon gas tank or something? see how much fuel is pumping out, like how many gallons per minute / or half minute, maby able to eliminate or varify faulty or dead fuel pump
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
A fuel pressure gauge can be teed in at the fuel filter. I believe the professional gauges connect at both the front and the rear of the front TB. I have permanently installed a tee fitting with a Schrader valve in the fuel line between the two TBs. There is no need for a "bench flow" test of the fuel pump. The regulator returns unneeded fuel back to the tank via the return line. The pump can be powered up, anytime, by running 12 volts to terminal "G" of the ALDL. You can test the pump volume by going for a test drive while observing the fuel pressure gauge. If the pressure doesn't drop, while you place the greatest demand that you can on the fuel system, the volume is sufficient. If the pump can't meet the demand, it is time to trouble shoot why. It may be as simple as a fuel filter, the sock, a kink in a fuel line, or it may be time for a pump.
RACE ON!!!
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Safety Car
Joined: Nov 2005
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From: Arizona - If you don’t know CFI, STOP proliferating the myths around it...
then set it to 14psi and do the same thing". It's better to replace the pump to an 85 pump if your stock pump "can not" provide a constant 14psi. The higheer the RPM, the larger the load. If you blip the throttle while watching the FP gauge and the needle drops, the pump is probably weak or the filter/sock is partley blocking the fuel or all the above.The FP gauge is normally installed between the front and rear TBs and is adjsuted at the rear TB via FP regulator as long as the anti-tamper plate in the regulator is removed.
A TB rebuild kit can be bought from Autozone that will do both TB completely "including diaphrams" from about $45, PN 96-629
Vacuum leaks are very common as mentioned and some bolts on the top plate may be only finger tight...it happens, so tighten them up. I would have also drained the tank after that many years of old gas, even with STABIL gas treatment in the tank.
Last edited by Buccaneer; Aug 1, 2007 at 07:41 PM.
Le Mans Master
Joined: May 2006
Posts: 9,226
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From: Irvine Ca
Also note, the electrical system is also suspect. You may just want to look under the distributor cap for burn marks
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by Buccaneer
The higheer the RPM, the larger the load. If you blip the throttle while watching the FP gauge and the needle drops, the pump is probably weak or the filter/sock is partley blocking the fuel or all the above.
RACE ON!!!