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Canuck Tech
Canuck Tech, Auto Service Technician
Category: Ford
Satisfied Customers: 536
Experience:  Red Seal Journeyman Technician, 20 Years experience
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I have a 88 mustang 5.0... I've done a complete over haul

Customer Question

Hello
JA: Hello. What seems to be the problem?
Customer: I have a 88 mustang 5.0... I've done a complete over haul with trick flow upper kit... when I turn my a/c on it dies at idol
JA: Are you fixing your Mustang yourself? What have you tried so far?
Customer: Mostly myself but a few mechanic friends when available
JA: Anything else you want the mechanic to know before I connect you?
Customer: No that's about really
Submitted: 1 month ago.
Category: Ford
Expert:  Canuck Tech replied 1 month ago.

A couple of possibilities. I'm assuming that it all worked before the modifications. The idle air control valve allows extra air into the engine when a load such as the A/C is placed on the engine. If the idle air control system isn't functioning properly, either because it was removed, or the valve itself is faulty, or there is a wiring issue, the engine will stall when the AC is turned on.

I'm also assuming that if you are driving down the road, and you turn on the ac, that the engine carries on, and the AC works! This would rule out a seized AC compressor.

The engine computer also needs a signal to tell it to increase the idle speed. You have made no mention of computer or wiring modifications.

If the system worked before the engine modifications, then something happened during the installation.

Hope that helps. Send me a note if you need more information. Canuck.

Expert:  Canuck Tech replied 1 month ago.

How is your Mustang repair going?

Customer: replied 1 month ago.
It was the one of the only things I haven't replaced on the new setup.. it was original to the car when I bought it.. the car didn't have a compresser when I bought the car so I replaced everything when it. Ike's to the A/C except the idol control.. so I'll definitely pick up a new one to see if that fixes my issues..
Customer: replied 1 month ago.
I've run into another problem before I even know if that idle air control.. The car died after going down to zero RPMs after being at a high rpm coming to a stop sign and we cannot get the car to crank back up now... we have gone through so many scenarios trying to get the car to crank but with no luck.. we have power to the coil but no spark
Expert:  Canuck Tech replied 1 month ago.

OK - so does the engine turn over by the starter, or it won't crank over at all?

Expert:  Canuck Tech replied 1 month ago.

Have you checked for spark?

Customer: replied 1 month ago.
After days of trouble shooting it turns out the distributor was bad even though it was only a few months old.. it cranked up immediately once we put the new distributor in... the IAC seemed to have fixed the A/C dying at idle but the car is still running flat in second and wants to die when the rpm drops going into neutral as you start to slow the car down to a stop before you down shift..!
Expert:  Canuck Tech replied 1 month ago.

Checked fuel pressure? Verified ignition timing with the new distributor? Cleaned the mass airflow sensor?

Customer: replied 1 month ago.
Fuel pressure is at 40.. times no is around 14
and checked the mass air flow.. this has been my main problem that we've been trying to fix before I ran into the situation that we first talked about..
Expert:  Canuck Tech replied 1 month ago.

14 psi fuel pressure?

Expert:  Canuck Tech replied 1 month ago.

i see - timing is at 14...

Expert:  Canuck Tech replied 1 month ago.

After looking at the wiring, I don't think this car has a mass airflow sensor... I'll check again...

Customer: replied 1 month ago.
I did a mass air conversation
Expert:  Canuck Tech replied 1 month ago.

OK. I'm assuming there was a computer change to go with the mass air conversion...

Customer: replied 1 month ago.
Correct.. A9L
Expert:  Canuck Tech replied 1 month ago.

Is there still a vacuum line going to the fuel pressure regulator?

Customer: replied 1 month ago.
There is
Expert:  Canuck Tech replied 1 month ago.

when you snap the throttle, does the fuel pressure go up?

Customer: replied 1 month ago.
I haven't noticed to be honest
Expert:  Canuck Tech replied 1 month ago.

The idea with the fuel pressure regulator is that as manifold pressure goes up (you are stepping on the throttle) the fuel pressure needs to go up as well. Should be about a 7 psi difference between closed throttle idle, and key on, engine off. Under what conditions did you measure 40 psi?

Customer: replied 1 month ago.
When we hooked up the fuel pressure gauge to the fuel line in was at 40
Expert:  Canuck Tech replied 1 month ago.

key on, engine off? Or engine running?

Customer: replied 1 month ago.
Off
Customer: replied 1 month ago.
Could this have anything to do with the mass air conversion and the VEhicle speed sensor
Expert:  Canuck Tech replied 1 month ago.

Alright. So we need to verify if the regulator is working. If you can get a number with the key on, engine off, and then a number at idle, that is a good start. The system also needs to be able to hold pressure, which if it doesn't can be an indicator of other fuel system issues. Typically, an engine going "flat" indicated a fuel delivery issue - going lean for some reason -

Expert:  Canuck Tech replied 1 month ago.

Do you have a functional vehicle speed sensor?

Customer: replied 1 month ago.
I put a adjustable fuel regulator in a 225 per hour liter fuel pump
Customer: replied 1 month ago.
I'm just hearing about the VSS sensor today from a friend.. so I'm not very familiar with it
Expert:  Canuck Tech replied 1 month ago.

OK. So we still need to verify the fuel regulator is changing the fuel pressure as the throttle is opened. VSS is an input to the computer.

Customer: replied 1 month ago.
Ok would it be better when I'm arounf the car
Customer: replied 1 month ago.
Oh ok.. the sensor that's goes into the transmission?
Expert:  Canuck Tech replied 1 month ago.

You have many variables in this car. Could it be the mass air conversion? Possibly. But check out fuel pressure first. I would like to see about 45 psi key on, engine not running, it holding pressure, and then down to about 38 psi at idle. Let me check on the vss wiring...

Customer: replied 1 month ago.
Let me know when you want to do a phone call
Expert:  Canuck Tech replied 1 month ago.

I don't know that the vss would give you the symptoms you have described. I see on the diagram that this car did come with a mass airflow stock.

Customer: replied 1 month ago.
I have a 1988 model which was still the speed density year... 1989 and up is when they became mass air
Expert:  Canuck Tech replied 1 month ago.

OK, so it has a different computer, and that was part of the mass air conversion? Is it a larger mass airflow sensor? I'm also wondering about the computer and its compatibility. I want to have some answers before we chat, because at that point... you are committed with cash! LOL

Expert:  Canuck Tech replied 1 month ago.

Ok. I'm looking at a 1988 diagram, and its got a MAF, but all good.

Customer: replied 1 month ago.
I put it the mass air conversion offered by LMR
Which required a 89 or newer ECM.. which I did all of that.. I hand 30# ***** which my mass air meter is calibrated for
Expert:  Canuck Tech replied 1 month ago.

Let's verify that fuel pressure... so long as the processor has a program for those injectors, it should work out. As part of the conversion, did the MAP disappear?

I've gotta take off for awhile, but I can check in later if that is OK...

Customer: replied 1 month ago.
Yeah no problem.. will you be available during the day when I can be at the car?
Expert:  Canuck Tech replied 1 month ago.

Yes, to a certain extent. You can do the fuel check and get back to me tomorrow. No problem.

Customer: replied 1 month ago.
Will do
Customer: replied 1 month ago.
Thank you for your help
Expert:  Canuck Tech replied 1 month ago.

Happy to help. I'll check back in periodically today.