Hard starting problem (Page 1/2)
Mike in Sydney AUG 06, 09:12 PM
I’ve searched the archives and haven’t found a definitive answer so I’m asking for advice.

My ‘86 SE with 45000 miles has a hard starting issue. Before I purchased it, the car had been sitting for 10 years. When I took possession l replaced the brake system completely, new cap, wire, plugs, distributors & ICM. It has a new fuel tank, pump, sending unit, strainer, filter, lines etc. Timing has been set correctly (with the jumper in place ).

The fuel pump primes when the key is turned and the system hold about 40 psi when stopped.

When cranking, the car takes several attempts to get it to fire. When it finally starts you have to play with the throttle to keep the car running. When warm, the car cranks and starts easier but it’s not a as easy as my ‘86 GT with 106,000 miles.

I’m thinking I have 1 or more faulty injectors. I have a new set of 6, 15# injectors I’m thinking of installing. Before I get into this, is there something else I should look at ?
Patrick AUG 06, 10:15 PM

Mike, I'd make sure the Manifold Air Temperature and the Coolant Temperature Sensors are both reporting the correct temperature to the ECU. If either one or both are reporting erroneous high temperatures, the air/gas mixture won't be rich enough for a cold start.

If they check out okay, make sure the cold start injector switch and the cold start injector are doing their job... but I would suspect one or both of those sensors first.
Mike in Sydney AUG 22, 09:27 PM

quote
Originally posted by Patrick:


Mike, I'd make sure the Manifold Air Temperature and the Coolant Temperature Sensors are both reporting the correct temperature to the ECU. If either one or both are reporting erroneous high temperatures, the air/gas mixture won't be rich enough for a cold start.

If they check out okay, make sure the cold start injector switch and the cold start injector are doing their job... but I would suspect one or both of those sensors first.




MAT and Coolant temp sensors appear to be working fine. The car is starts easier when warm but you have to play with the throttle. If you give it too much gas, it stumbles and dies if you feed the gas in slowly until it reaches 17-1800 rpm then it takes off and drives like it just came off the assembly line.

There are no codes from the ECU other than the 1-2 code confirming the ECU is o.k.

I have to say, I’m stumped. I’m wondering if the Idle Air Control is faulty or out of adjustment. I haven’t replaced fuel injectors yet but I’m not discounting that…

[This message has been edited by Mike in Sydney (edited 08-22-2024).]

Patrick AUG 22, 11:42 PM

quote
Originally posted by Mike in Sydney:

The fuel pump primes when the key is turned and the system hold about 40 psi when stopped.



How long does it hold that pressure when the fuel pump stops?


quote
Originally posted by Mike in Sydney:

If you give it too much gas, it stumbles and dies if you feed the gas in slowly until it reaches 17-1800 rpm then it takes off and drives like it just came off the assembly line.

I’m wondering if the Idle Air Control is faulty or out of adjustment.



IMO, the IAC would have nothing to do with those issues mentioned above.

My next guess (if the fuel pressure isn't dropping too quickly) would be the MAP sensor. It's been suggested many times over the years here to temporarily unplug the MAP sensor (I'm assuming the reference is to the electrical connection, not the vacuum line) and see if the engine runs any better in a limp mode default setting for the MAP. That test has never worked for me, as my engine(s) wouldn't run at all with the MAP unplugged... but try it and see what happens.

[This message has been edited by Patrick (edited 08-22-2024).]

Mike in Sydney AUG 23, 09:38 AM
Car has a new fuel, tank, pump, sender, etc. I can hear the pump prime and continue to run when the car is started. I need to check the residual pressure and how long it takes to leak down. Ive also installed a new MAP sensor. I’ll try unplugging it to see if there is any change. It could be faulty out of the box.

I have to admit, I’m stumped. It doesn’t act like a typical vacuum leak because after it it warm the idle drops to 8-900 when it is in neutral. Doesn’t like to hold an idle while in gear. Sometimes it idles higher but a tap on the throttle drops it down. When cold, putting it in gear is an issue. It dies unless you give it some throttle.
Patrick AUG 23, 03:50 PM

quote
Originally posted by Mike in Sydney:

Doesn’t like to hold an idle while in gear. Sometimes it idles higher but a tap on the throttle drops it down.



Have you checked the TPS to make sure it has no dead spots?
Mike in Sydney AUG 23, 08:49 PM
Car has a new fuel, tank, pump, sender, etc. I can hear the pump prime and continue to run when the car is started. I need to check the residual pressure and how long it takes to leak down. Ive also installed a new MAP sensor. I’ll try unplugging it to see if there is any change. It could be faulty out of the box.

I have to admit, I’m stumped. It doesn’t act like a typical vacuum leak because after it it warm the idle drops to 8-900 when it is in neutral. Doesn’t like to hold an idle while in gear. Sometimes it idles higher but a tap on the throttle drops it down. When cold, putting it in gear is an issue. It dies unless you give it some throttle.
Patrick AUG 23, 09:07 PM

quote
Originally posted by Mike in Sydney:

Car has a new...



Mike, whatever you did while posting... don't do it again.

Mike in Sydney AUG 24, 08:12 AM
Freakin’ iPad.

(That’s my excuse and I’m sticking to it!)
Mike in Sydney AUG 25, 11:05 AM

quote
[B]Originally posted by Mike in Sydney:[/B

I’m wondering if the Idle Air Control is faulty or out of adjustment. I haven’t replaced fuel injectors yet but I’m not discounting that…




Well, it ain’t the IAC. I replaced it and there was no change.

I had the distributor replaced sometime back. The old one was badly rusted from sitting. (I purchased the car unseen and had my mechanic in the U.S. do some work to get it ready for shipment back home to Oz.). I’m now wondering if the mechanic may not have ensured number 1 was at TDC when he installed it. Number 1 position on the distributor appears to be further clockwise (3 o’clock vs. 1 o’clock) than on my GTs .