90 SC power loss WOT

Well, battery tests low CCA, confirms bad battery 75% health 12.4V charge engine off. ALT is putting out 14.3V at idle, 15.1 @ 2000rpm. Not sure what you mean by EMI? Factory unmolested harness, seems all intact, however about the grounds... does the factory small ground on the chassis in front of the battery have a link in it? So seems that my factory ground cable on the battery does no grounding at all. Hence the other grounding that I have put in place. I would like to get my hands on an EVTM or factory manual... however I have neither, only a Haynes manual, which has some useful info but not specific to supercoupe and doesn't help much.

So now you mentioned grounds, I may just check into that factory battery ground... then check grounds to the EEC and signal to the DIS. Tach is working fine, but you got me onto something, this is good. I hope it's something simple. And new battery is in the mix tomorrow as well.
 
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then check grounds to the EEC and signal to the DIS.

In that case....see http://mnharms.com/tutorials/disnostart/

EMI: see https://en.wikipedia.org/wiki/Electromagnetic_interference

At least one of the wires in the front/upper harness leading from the crank sensor is wrapped in shielding/foil. When that protection is removed/compromised, signals to/from the EEC can go out of spec and cause various issues, from misfires to no-start.

Donate that haynes to goodwill (it may be the one with the incorrect firing order, so...) and grab factory manuals. Google for sources, or try eBay.
 
So, grounds are all good, tested AMP draw from fuel pump while driving. Goes from 5.5A idle to 3.3A under load... which looks to me as if the fuel pump is not pushing like it should and may be on the way out. High Amperage would state a blockage in the filter as it's working too hard. Going to replace the fuel pump, and if that's not it, looks like an EEC issue that's causing a power drop across all sensors. See what happens when I get to it now I guess.
 
Goes from 5.5A idle to 3.3A under load... which looks to me as if the fuel pump is not pushing like it should and may be on the way out.

Quoting off the 'net "Mechanical resistance inside the pump can result in higher-than-normal average pump current. A clogged fuel filter or fuel line restriction will also increase pump current. Electrical resistance, either in the pump or elsewhere in its circuit, lowers available pump voltage and reduces pump current."

If in fact you did see 5.5a at idle and a reduced current of 3.3a under load (vs. 3.3a/idle & 5.5a/loaded), that would indicate high resistance in the circuit, which is not uncommon on these cars at the fuel pump connection/harness. If you do replace the pump (good idea regardless once you've dropped the tank), be sure to validate the wiring/connections, which might be the only real issue.
 
Yes I want to make sure good contact at and in the tank, however, the car ran great up until i changed the fuel filter... which is strange as it should have had better flow, and filter is the correct direction. I know grounds, power and everything at Bothl ends of the plug at the tank are good. My buddy told me should be around 5-7A as a good reading. Looking into a spare EEC just in case something there is going bad. Board looked good, traces good both sides. But the part that makes me think EEC is amperage drops at the FP at WOT, MAF voltage drops at WOT, TPS voltage drops aft WOT, losing everything after 5 mins driving under load at the same.points. It'll run at 60kmh in 5th at idle all.day long with no WOT issues, only when it's been seeing boost or load on the road. It's definitely a new issue I've never come across. All sensors are 100% just blowing me away on this one
 
No, just waiting to get pressure tester tomorrow, nobody has one here. Buddy going to lend me his.
 
So fuel pressure test is done, 38 psi at idle, under load drops to 19-20psi at the rail while driving. Comes back to 40psi when I let off throttle. Shut car off for 2 seconds, restart and fuel stays at 40psi for about 30 seconds under load then drops to 20 again. No vac leaks. That's where its screwy, if the pump was 100% on the way out, why would I get pressure back after key off and restart and have good fuel supply again. And in the meantime, my MAF and TPS read low voltage at the same time and follow the exact same trend as the fuel pump. It's like a total system voltage drop across everything.
 
issue resolved

So, after a poor fuel pressure rating, I found the pump to be defective. Swapped pump and no more issues, however, it was a new factory ford sending unit with a walboro pump (factory pump from the looks) and the last owner had a shop do the work. The connector on sending unit was broken to bits, so they tried to solder the terminals on the sending unit. Green death all around, and there was some sort of resistor installed between positive and negative pump wires to the sending unit. Not sure why that was done, but eliminated that and replaced the connector. I'm thinking that connection was the cause of the failure of the pump due to a man made short to ground.
 
Glad you sorted it out, thanks for the followup.

Wondering if that resistor had something to do w/the fuel gauge.

Was it reliable before and still ok now?
 
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