Vader inside, follow up to rich running problem...
03-30-2002, 06:43 PM
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Vader inside, follow up to rich running problem...
this is in continuance to the thread at https://www.thirdgen.org/techbb2/sho...threadid=84477
i finally got around to getting you those readings you asked for, and here they are:
fuel pressure:
12 psi - car off, ignition on
15 psi - car on, cold, idle
map readings:
from the two wires (purple and green)
4.62 volts @ 0 HG
1.30 volts @ 18 HG
from the two outside wires (purple and gray)
5.02 volts @ 0 and 18 HG
engine vacuum readings: (with vacuum line to MAP disconnected)
20 HG @ 1300 rpm, idle, cold, in park
16 HG @ 750 rpm, idle, cold, in gear
19 HG @ 750 rpm, idle, warm, out of gear
i used the vacuum line from the map sensor to take my vacuum readings, should i have left it connected and taken it from a different spot?
also, you said i should have at least 4.8 volts at 0 HG and i have only 4.62, is that out of spec enough to suspect the map sensor?
i finally got around to getting you those readings you asked for, and here they are:
fuel pressure:
12 psi - car off, ignition on
15 psi - car on, cold, idle
map readings:
from the two wires (purple and green)
4.62 volts @ 0 HG
1.30 volts @ 18 HG
from the two outside wires (purple and gray)
5.02 volts @ 0 and 18 HG
engine vacuum readings: (with vacuum line to MAP disconnected)
20 HG @ 1300 rpm, idle, cold, in park
16 HG @ 750 rpm, idle, cold, in gear
19 HG @ 750 rpm, idle, warm, out of gear
i used the vacuum line from the map sensor to take my vacuum readings, should i have left it connected and taken it from a different spot?
also, you said i should have at least 4.8 volts at 0 HG and i have only 4.62, is that out of spec enough to suspect the map sensor?
03-30-2002, 07:53 PM
#2
Lucas,
Idle vacuum looks good at hot idle. The fuel pressure looks a little above specification, and the MAP may be a bit on the low side. Under perfect conditions, the MAP signal should fall within these ranges:
Unfortunately, the MAP is not a perfectly linear output device. Theoretically, you should read 5.0V from the MAP at 1 BAR (no vacuum), and 4.78V is the tolerance (5%). The signal level seems a little low, so if you are only a little rich, that could be contributing. Couple that with a slightly high fuel pressure, possibly sluggish or cold O² sensor, a TPS that is adjusted a little on the high end of the range, maybe a little PCV blockage, and some injector wear, and you could be on the rich side.
Since your '88 should still have an adjustable TPS, have you tried to set it a little toward the low end of the range? Try 0.48-0.54VDC for an idle setting.
A new MAP sensor should get your signal back to a little better level, although the voltage at hot idle with 18" Hg appears to be very reasonable.
The fact that this is an intermittent problem is more confusing, and may be related to a poor electrical connection at the CTS, MAP, oxygen sensor connections (or ground), or even the remote possibilities of ground leakage in the injector circuit, sticking injector(s), or a sticking fuel pressure regulator. It's a lot easier when they just outright break.
Have you had an A/F ratio test to determine just how rich it is? It may be an option, and probably should have been done by the testing shops.
I'm just throwing out possibilities, since I would have actually expected a lot lower MAP voltage as part of your problem. You are running stock injectors, correct?
Idle vacuum looks good at hot idle. The fuel pressure looks a little above specification, and the MAP may be a bit on the low side. Under perfect conditions, the MAP signal should fall within these ranges:
Unfortunately, the MAP is not a perfectly linear output device. Theoretically, you should read 5.0V from the MAP at 1 BAR (no vacuum), and 4.78V is the tolerance (5%). The signal level seems a little low, so if you are only a little rich, that could be contributing. Couple that with a slightly high fuel pressure, possibly sluggish or cold O² sensor, a TPS that is adjusted a little on the high end of the range, maybe a little PCV blockage, and some injector wear, and you could be on the rich side.
Since your '88 should still have an adjustable TPS, have you tried to set it a little toward the low end of the range? Try 0.48-0.54VDC for an idle setting.
A new MAP sensor should get your signal back to a little better level, although the voltage at hot idle with 18" Hg appears to be very reasonable.
The fact that this is an intermittent problem is more confusing, and may be related to a poor electrical connection at the CTS, MAP, oxygen sensor connections (or ground), or even the remote possibilities of ground leakage in the injector circuit, sticking injector(s), or a sticking fuel pressure regulator. It's a lot easier when they just outright break.
Have you had an A/F ratio test to determine just how rich it is? It may be an option, and probably should have been done by the testing shops.
I'm just throwing out possibilities, since I would have actually expected a lot lower MAP voltage as part of your problem. You are running stock injectors, correct?
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