Cold start problem after a swap
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Cold start problem after a swap
I swapped a 93 4.6 into a 48 IHC. With alternator off it starts and runs like a dream. With the alternator hooked up, it starts and dies or has major lope before dying. After 4-5 min, it works great. Any ideas?
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cold start
All of these are in order. the key appears to focu on a change in voltage from around 12 before the alternator kicks in and 14.6 after. additionally, once the engine warms a little it runs perfectly regardless of voltage input.
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Originally Posted by terrys
All of these are in order. the key appears to focu on a change in voltage from around 12 before the alternator kicks in and 14.6 after. additionally, once the engine warms a little it runs perfectly regardless of voltage input.
The alternator puts out A/C voltage (alternating current) which is passed through the rectifier bridge and changed to pulsing D/C (direct current) like the battery.
If there is resistance between the battery and the alternator, and somewhere in the middle is the PCM (ECU/computer), the ripples from the alternator charging can drive a computer crazy.
Check all your grounds... the PCM may not be grounded correctly, and it's getting interference from the alternator. There should be one from the battery to the engine, and from the engine to the body/frame. Where is the PCM grounded to? If it's to the body, run a ground wire directly to the (-) side of the battery and see if that helps.
With the alternator disconnected, if you put any sort of load on the motor (like putting it in drive with an auto, or putting it in gear and slipping the clutch slightly), does it stall out? That will tell you if it's a load-related problem or an electrical/alternator problem.
Keep it coming!
art k.
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Thanks, some great info. I swapped in all of the engine compartment wiring and was very concerned about grounds. PCM ground is located on a post on the firewall, this ground is also connected via a grounding cable to the engine block. Connections are all soldered with shrink wrap and are secure/checkout well. I am not able to check under load yet but based on the acceleration. and other characteristics I suspect it is good. The only difference appears to be a cold engine with alternator working
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What size wire did you use for the grounds?
I'd still like you to try ground the PCM directly to the battery instead of going to the firewall, and then to the engine, and back to the battery.
For that matter, where's the +12V for the PCM coming from?
I'd still like you to try ground the PCM directly to the battery instead of going to the firewall, and then to the engine, and back to the battery.
For that matter, where's the +12V for the PCM coming from?
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The wire is the stock #14 Black-white (If I remember right - cct 875) I will re-ground to battery as you suggest. PCM feed comes via the standard ford circuit. Main power to PCM relay is from eng compt fuse box (Yellow feed), Actuating feed is supplied via ignition to red - green through eng compt fuse box as per Helm diagram. Voltage from battery and alternator is constant with no apparent fluctuations.
Keep the ideas flowing, I appreciate the help and insight. What would you think about changing the charge to battery temporarily via a charger?
Keep the ideas flowing, I appreciate the help and insight. What would you think about changing the charge to battery temporarily via a charger?
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If the original ignition used a resistor wire, any chance you left that in there somewhere?
Just throwing out ideas at this point.
I don't know about using a charger seperately... you could try it ...
Just throwing out ideas at this point.
I don't know about using a charger seperately... you could try it ...
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I have checked grounds, put a ground wire direct to PCM ground, re-evaluated fuel supply by changing the feed pump and have disconnected the battery temorarily to restart the PCM. The first items made no change but I am hopeful the the rebooted PCM is going to work. I will try another cold start in the morning to assess changes in the computor
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I built the fuel system to function as an original; 3/8 feed line, 5/16 return and carbon canister as well. Main Fuel pump pump is stock '89 ford inline 40-45 PSi and fed by a Carter high volume low pressure. I have tried another pump with even lower volume but this made no difference. I believe the cause has to centre on the cold start but am not sure where to go next. The fact that it runs terrific once a basic warm up of 4-5 minutes is complete really mystifies me.
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Your MAF could be out of range, and with the lower voltage without the alternator the readings could be down to where they should be.
Is the MAF in correctly, (facing the right way), do you know for sure it is working correctly, is it clean?
I don't know if this is for your engine, but the 95 T-Bird 4.6 MAF voltage readings are as follows:
Voltage between wires A & B is 10.5 volts.
Voltage between wires C & D is .34 to 1.96 at idle.
Is the MAF in correctly, (facing the right way), do you know for sure it is working correctly, is it clean?
I don't know if this is for your engine, but the 95 T-Bird 4.6 MAF voltage readings are as follows:
Voltage between wires A & B is 10.5 volts.
Voltage between wires C & D is .34 to 1.96 at idle.
Last edited by yardbird; Nov 22, 2005 at 03:47 PM.