1986 944NA strange idle, hesitation issues
06-22-2018, 06:31 PM
#1
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Thread Starter
1986 944NA strange idle, hesitation issues
Hi,
I had a leaking fuel injector in my 1986 944 NA. I bought new OE injectors and installed those. While doing so, I noticed the vacuum line behind the Y-connector running back from the fuel dampener and pressure regulator was melted/crushed. I replaced the vacuum lines from the rail back to the their origin at the control valve.
After everything was done, the car fired up as normal, and idled smoother and at lower RPM (from 1100 to 900) than before the changes. I took it for a 10 minute drive and noticed a bit more hesitation during acceleration than before, but nothing too drastic.
The next day, I started the car and it started...weakly. It had to turn over 5 or 6 times, then when it started it didn't "fire up" but sort of whimpered to life, and idled at about 600 RPMS (example:
).
After a couple minutes of idle like this it smooths out, maybe after giving it a bit of gas (
) .
However, the engine than goes into mode 2 (
). The engine starts to almost quit, rev up, almost quit. It does this for about two minutes, then smooths out.
After smoothing out, it idles at about 1000 RPMs and is fairly smooth (
) . It does seem to miss here and there. When driving, I have to give it quite a bit more gas when starting in first gear than I used to, or it almost stalls. Acceleration is hesitant between 2 and 3k RPMS, then seems to smooth out. Power is about the same as before.
The car is drivable, but not at its best. It also sounds like it has a big vacuum leak, though I'm doubting myself on how it sounded before I made the changes. I sprayed carb cleaner around everything I could reach and found nothing. Today I fixed a couple exhaust leaks, and no changes. Before changing the injectors and vacuum hoses, the car would start fine after two cranks, sputter at bit at first, then idle at 1100 RPMs (none of the almost stalling behavior).
Thoughts on where to start?
Thanks!
Brennan
I had a leaking fuel injector in my 1986 944 NA. I bought new OE injectors and installed those. While doing so, I noticed the vacuum line behind the Y-connector running back from the fuel dampener and pressure regulator was melted/crushed. I replaced the vacuum lines from the rail back to the their origin at the control valve.
After everything was done, the car fired up as normal, and idled smoother and at lower RPM (from 1100 to 900) than before the changes. I took it for a 10 minute drive and noticed a bit more hesitation during acceleration than before, but nothing too drastic.
The next day, I started the car and it started...weakly. It had to turn over 5 or 6 times, then when it started it didn't "fire up" but sort of whimpered to life, and idled at about 600 RPMS (example:
After a couple minutes of idle like this it smooths out, maybe after giving it a bit of gas (
However, the engine than goes into mode 2 (
After smoothing out, it idles at about 1000 RPMs and is fairly smooth (
The car is drivable, but not at its best. It also sounds like it has a big vacuum leak, though I'm doubting myself on how it sounded before I made the changes. I sprayed carb cleaner around everything I could reach and found nothing. Today I fixed a couple exhaust leaks, and no changes. Before changing the injectors and vacuum hoses, the car would start fine after two cranks, sputter at bit at first, then idle at 1100 RPMs (none of the almost stalling behavior).
Thoughts on where to start?
Thanks!
Brennan
06-23-2018, 03:04 AM
#2
Rennlist Member
If you have not yet already, suggest you replace all of the 3mm vacuum lines under the hood. After 32 years, all of the rubber bits/vacuum lines are suspect, including the 10mm line from the brake booster, the 10mm lines going to the idle control valve [ICV], and the J-boot [which develops crack on its underside].
Speaking of the ICV, sounds like yours may be gummed up. Folks have had varying success attempting to clean it with carb cleaner...certainly can't hurt to try.
Speaking of the ICV, sounds like yours may be gummed up. Folks have had varying success attempting to clean it with carb cleaner...certainly can't hurt to try.
06-24-2018, 01:04 PM
#3
AutoX
Thread Starter
Update: When I replaced the vacuum lines, I noticed the original line behind the T-connector running to the fuel regulator and damper was melted shut. Therefore, no vacuum had been going to either part on the fuel rail prior to this.
I pulled and blocked both vacuum lines from the rail and the car started on two cranks like it did before. I reconnected the lines, and let the engine warm up. When it got to the point of almost stall, rev up, almost stall, rev up, I again pulled and blocked those lines, and the idle smoothed out immediately. I'm thinking my fuel pressure regulator is not supplying a constant pressure.
I pulled and blocked both vacuum lines from the rail and the car started on two cranks like it did before. I reconnected the lines, and let the engine warm up. When it got to the point of almost stall, rev up, almost stall, rev up, I again pulled and blocked those lines, and the idle smoothed out immediately. I'm thinking my fuel pressure regulator is not supplying a constant pressure.
07-08-2018, 10:51 AM
#4
AutoX
Thread Starter
RESOLVED:
It finally occurred to me to check the resistance across the terminals of the injectors I had installed. They are high impedance 16 ohm injectors! I got a new low impedance injector (measured 2.5 ohms) and put the three good originals + the new one and everything is fine now. Car is running much better with four correct injectors + the replaced and properly connected vacuum lines.
Brennan
It finally occurred to me to check the resistance across the terminals of the injectors I had installed. They are high impedance 16 ohm injectors! I got a new low impedance injector (measured 2.5 ohms) and put the three good originals + the new one and everything is fine now. Car is running much better with four correct injectors + the replaced and properly connected vacuum lines.
Brennan
