5.0 ho cold start and idle surge issue - Ford Mustang Forum
 
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post #1 of 14 (permalink) Old 03-17-2009 Thread Starter
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5.0 ho cold start and idle surge issue

Maybe someone here can help, im a chevy guy by nature (i know boooo) but have taken on a mustang "project" for a co worker, and rest assured no good deed goes unpunished, to make a long story shorter here is the rundown of the problem and the things i have checked and or replaced.....

the basic problem is two fold and i believe related, the first is cold start, it will not start cold and idle, it just shuts off, if you hold the rpm up and build a little heat it will sort of idle, which brings us to the second problem, once warm, it will idle fine, and then all of a sudden drop or stall all togeather, if you blip the throttle it will recover and idle fine for another few mins....the motor acts like its idling rich tho it doesnt belch the tell tale black smoke when you whack the throttle, here are a list of things i have checked or replaced and adjusted

new plugs and wires
new tps (voltage adjusted key on engine off green/black wire to .999v)
proper map sensor is verified (i dont know how to test functionality)
new thermactor
new appearing iac motor (ive heard it called iapv) when disconnected the idle still surges
correct mass air sensor, cleaned, and proper for a 19lb system (dont know how to test functionally)
new 19lb injectors
new fuel pressure regulator
egr valve appears to be working, but the idle still surges weather its plugged in or not
new o2 sensors
i have checked and replaced all the applicable vaccum lines and there is not a vaccum leak that i can find, and its not leaking from the brake booster either

i have the feeling that someone before the present owner chased this problem because the mass air sensor and the iac motor appear to be new, the temp sensors appear to work, but i have no idea,
to be blunt im in over my head,
my snapon mt2500 scanner, will not communicate with the eec iv thats in the car...im lookin to the distributor module now, and possibly the eeciv itself, any ideas or things i may have missed, im not a ford guy but will be by the time this is all done
thanks in advance
Bill
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post #2 of 14 (permalink) Old 03-17-2009
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What year is this car? Have you checked the throttle body itself? It may need a trip to a Ford dealer, might save you a ton of time, which is money in my book...
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post #3 of 14 (permalink) Old 03-17-2009
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is engine light on? what codes does it read? is it stock? wats the timing siting on what degree? stock is 10 degree how does it drive does it ride lost of power? hows the fuel pressure? how many miles on it does it have oil on the sparplug?
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post #4 of 14 (permalink) Old 03-18-2009 Thread Starter
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What year is this car? Have you checked the throttle body itself? It may need a trip to a Ford dealer, might save you a ton of time, which is money in my book...
the car chasis is an 89lx, i feel the car is a conversion, and yes the throttle body was a donor off a working car. Agreed about the ford dealer, except i get the feeling that the local dealers dont want anything to do with cars over 10yrs old, and an inexperienced tech on my dime gets expensive quick
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post #5 of 14 (permalink) Old 03-18-2009 Thread Starter
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Quote:
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is engine light on? what codes does it read? is it stock? wats the timing siting on what degree? stock is 10 degree how does it drive does it ride lost of power? hows the fuel pressure? how many miles on it does it have oil on the sparplug?
the engine light is intermittent, and i havent been able to get the codes, gonna work on that today or tommorrow, i have no way of knowing if it is stock, it is possible that someone put a cam in the motor before i got ahold of the car, the timing is 12* which is supposed to be stock for the ho motor, fuel pressure is unknown, and the plugs were replaced when i had the motor out (replaced all the gaskets, rear main, oil pan etc....) but i'll check them
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post #6 of 14 (permalink) Old 03-18-2009
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Take any Vacuum readings?
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post #7 of 14 (permalink) Old 03-18-2009
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you could try setting the idle
Attached Files
File Type: pdf idlesettingprocedure.txt.pdf (145.0 KB, 491 views)

1988 Mustang GT, TTops, 306, AOD with 4r70w gears, shiftkit, E303, FR Shorties, BBK H-pipe, Flowmaster Cat Back, 3.73's, Trac Lok with F150 spring, Eibach springs, B&M Tork Master 2400 Converter, C&L 76mm Mass Air, Accufab 70mm TB, TMoss Ported Explorer Intake, K&N Air, Wix Oil, Mass Air, Subframe connectors, Poly Bushings, AFR 165 Heads, 24lb injectors, Scorpin 1.6 RR = 270HP, 296TQ at the tires.
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post #8 of 14 (permalink) Old 03-18-2009 Thread Starter
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yes, at 1k its pulling 14kpi (i think thats the right designation), at 800 about 10,

a little more history, when the car arrived at my house, it was leaking everything from everywhere, vaccum leaks, all over, oil, coolant, tranny fluid, i pulled the engine/trans, and resealed EVERYTHING, valve covers, intake (upper and lower) throttle body, smog spacer, new oil pan and gasket, new rear main, new trans seals front and rear, new trans pan gasket, new rack and pinion, all new hoses, (coolant and vacum)

The car had this problem before i took it all apart, i figured vaccum, combined with a sensor or two, but now im reasonably sure there are no vacum leaks and as reasonably sure the sensors are good, new map, new thermactor, new iac, new tps, and a mass airflow sensor from a known working car (yes its the correct working car)

im in the process of trying to get the codes, and am waiting on a donor distributor and computer (also from known working car) im just at wits end, i was hoping this was a common ford thing, but apparently not....
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post #9 of 14 (permalink) Old 03-19-2009
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With motor at idle vac pointer should hold steady between 16 and 22. A steady low reading (10) indicates late ignition timing or intake manifold air leak. Is there any aftermarket parts? Heads or intake?
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post #10 of 14 (permalink) Old 03-19-2009 Thread Starter
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Quote:
Originally Posted by gbmust92 View Post
With motor at idle vac pointer should hold steady between 16 and 22. A steady low reading (10) indicates late ignition timing or intake manifold air leak. Is there any aftermarket parts? Heads or intake?
one of the problems with the vacum reading is the car wont hold a steady idle, it is constantly surging (in about a 10/15 sec cycle) between 600 and 1100 rpm, if i drop the high (1100) down to 800 the motor stalls, but to answer your questions,
the heads and intake are stock, the cam however is suspect, it lopes at idle, and its not from missfire or dropped injector, if the person before me put a (big) cam in it, it would deffinately drop the vaccum numbers, as well as monkey the rest of the works, my understanding with these cars is you cant arbitrarily change something of that nature without modding the ecs profile to match the cam....
the ignition timing, has me concerned, if the distributor is bad (out of spec or funky internal electronics) that would certainly account for my problem.....
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If it's the cam, I don't know if that would account for a drop in vacuum all the way down to 10...my understanding is that you'd probably be around 14-15 and you'd have some very slight oscillation of the needle to show the different valve lift/overlap. I have to agree with above; if you're down as low as 10 at idle (which should usually be around 750-800, so I would be a bit more trusting of a vacuum number you see at that RPM), it sounds like you still have a leak somewhere in the system, whether you've done the extra tuning to the electronics or not.

As another example, I'm currently dealing with a '86 Bronco with essentially the same engine (definitely all stock) that has a slight surge issue, but even when it surges low the vacuum NEVER drops below 15.

Maybe a combination of issues with the timing AND the cam?

1983 Mustang GT convertible -- under restoration
Previous models owned:
1980 3.3L I6 notchback (my first car...sigh)
1996 3.8L V6 coupe
(NOTE: the '96 replaced a '95 coupe I had that was thoughtfully totaled...after I had owned it all of 6 days...by a lady who was thinking about Christmas shopping instead of driving)
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Or what if the valve timing itself is screwed up? Is there maybe some slack in the timing or something that, even with a stock cam, could have screwed that up and gotten it off just enough to cause the issue?

1983 Mustang GT convertible -- under restoration
Previous models owned:
1980 3.3L I6 notchback (my first car...sigh)
1996 3.8L V6 coupe
(NOTE: the '96 replaced a '95 coupe I had that was thoughtfully totaled...after I had owned it all of 6 days...by a lady who was thinking about Christmas shopping instead of driving)
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post #13 of 14 (permalink) Old 03-19-2009 Thread Starter
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thats something i havent thought of, thanks, i'll retime the motor from scratch when i install the new distributor, it is possible, there is a vaccum leak, but if there is i cant find it, as i said before, i have resealed and replaced all engine components even remotely capable of leaking anything, on the plus side it doesnt leak any fluid anywhere any more....yay
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post #14 of 14 (permalink) Old 04-01-2009 Thread Starter
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Finally! Success!

Ok, figured id share what the ultimate problem was, since i hate reading threads that have no resolution....

The winner is the fella who said vacum leak..ding ding ding

there are six bolts holding on the upper intake to the lower intake, the front and rear were not oem bolts (unbeknownst to me) and were bottoming out in the holes, nt allowing the manifold to torque properly, so i spaced em up w/ a few washers and then discovered that somehow the upper (or lower) was slightly warped, so instead of tearing it all down, and sending it out to the machine shop, i took a trick from outboard motors, i replaced the gasket with a new one, and used some gel seal (loctite 518 anerobic gasket maker) on both mating surfaces, and voila, sealed up fine, car runs right as rain.....

Thanks to all who offered advice and help, it was appreciated
Bill
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