TurbosaurusRX

iTrader: (3)

I've been trying to track down some FD problems in the past few weeks and I believe I'm getting closer to a fix. My problem at this point is a buzzing ISC valve.

Just as a background, my car has been sitting for quite some time and I've turned my attention to finding out the source of the problem. The problem started when I took the car out for a drive one day. After warming it up, I took it down the road, hopped on the highway, and suddenly the backfires began. I couldn't accelerate at all... any press of the gas pedal resulted in backfiring. I limped it the short way back home and parked it.

Fast forward to now. The car started last week, idled for 2-3 minutes then began sputtering. The idle would drop and, right before stalling, shoot up again. This cycle would repeat with the idle dropping lower each time until it finally stalled... and would not restart. The car turns over after sitting for few days it seems, but the symptoms are the same (dropping idle, no restart afterwards, etc). FYI, I'm tuned on a Power FC, 850cc primaries and secondaries, full non seq.

I've checked a few things up to this point:
- Installed a fuel pressure gauge (jumpering F/P to ground results in a 38psi reading which is solid according to the FSM. Hold test checks out. After 5 minutes, fuel pressure is still above 21psi.)
- Compression test (with a conventional piston tester) results in even bounces during the test

On to the ISC valve info:
- The valve has been soaked in carb cleaner overnight
- The valve operates just fine when connected directly to a battery
- Resistance across the valve is within spec according to the FSM
- The connector wire to the ECU has continuity
- Key 'On' shows voltage within spec at the ISC valve wiring

What is boggling me is the buzzing sound the ISC makes only after I've tried starting the car (can be heard in my video ). I back-probed the pin on the ECU to see what was happening during the buzzing and the voltage drops down to around 2.6V.

If any of this info is relevant:
- My dashpot is not touching the throttle at any point
- My Rev/Idle settings in the PFC are as follows:
F/C A-E 1100
F/C E/L 1150
F/C A/C 1250
Idle A-E 900
Idle E/L 930
Idle A/C 955

I don't have a datalogit currently, so I can't view or post logs up. Does anyone have any thoughts regarding the voltage drop/buzzing issue? I'm at a bit of a loss on where to attack next.

Peruvianrx7

iTrader: (25)

I would try another isc

TurbosaurusRX

iTrader: (3)

Oops, I completely forgot to mention that in my first post. I do have a second ISC that buzzes in the exact same fashion. It's certainly possible they are both somehow faulty, however the resistance tests within spec for both. I understand the ecu should be adjusting voltage to the ISC, but the 2-3 range doesn't seem right to me. Also, if I only crank the car for a short time then stop, the voltage doesn't drop (along with no buzzing).

Turk82

iTrader: (17)

I had my motor built about a year ago and when I got it back I noticed this same thing happening. My idle would surge as you said until it nearly died or did die and then the buzzing would start. I got the car to idle correctly and rev nice for 1 day and that was it. The next time I worked on it the idle did whatever it wanted and sputtered and misfired when the throttle was touched. I am curious to find out if this is the culprit.

TurbosaurusRX

iTrader: (3)

Turk, I'll definitely keep this thread posted on my progress. Hopefully it helps you figure out your issue as well.

Also, I don't know how I overlooked this before, but the B/W wire to the ISC valve comes off the EGI Main Relay. I'll check this wiring when I get home and see what may be going on there. Maybe there is an issue with the relay or even before the relay...

TurbosaurusRX

iTrader: (3)

Well the B/W wire coming off the ISC is getting 11.8V before and after cranking, so there doesn't seem to be any issue with the EGI Main Relay.

I'm completely confused by these scenarios and maybe I'm just not thinking about it correctly.

A) W/ the ISC valve plugged in:

Before cranking
1) Voltage is ~11.8V at the input wire (B/W)
2) Voltage is ~11.8V at the output wire (L/G)

After cranking and releasing key (ISC now starts buzzing)
1) Voltage is ~11.8V at the input wire (B/W)
2) Voltage is ~2V at the output wire (L/G)

(This scenario makes me think the problem is with the ISC valve... but what about the cranking creates this problem? It functions fine before cranking)

B) W/ the ISC valve unplugged:

Before cranking
1) Voltage is ~11.8V at the input wire (B/W)
2) Voltage is 0V at the output wire (L/G)

After cranking (same as above ~11.8V input / 0V output)

These values seem all correct to me. No ISC valve allowing power to flow across it, hence no voltage reading on the output side.

Now to what is flustering me. In scenario B, after cranking... I plug a completely separate ISC valve in and this one starts buzzing. This ISC valve was not even on the car during the cranking.

I can't for the life of me comprehend this. My thought is that the ECU is not supposed to send any voltage through this wire, but rather close the ISC valve circuit. But then how is the voltage supposed to change during idle?? (5V-11V according to the FSM) And if it is a signal wire, then why is no voltage sent to the ISC connector with the ISC valve unplugged (nor is there a voltage reading at the ECU during this time)??

As you can tell, I'm not an electrical guru, so my thinking could be completely off base here. Any thoughts on these scenarios or my logic??

Smokey The Talon

iTrader: (33)

Were you able to get any resolution to this? I'm having a VERY similar problem and have a different used ISC coming to me to test out. When driving the car lost power similar to running out of fuel so I thought that was originally the issue until I heard the ISC buzzing when I got it back in my garage.

Was the ISC your culprit alone, or was there another wiring/electrical issue you had to solve?

Smokey The Talon

iTrader: (33)

As a follow up I did 2 things regarding this issue
1) replaced the ISC with another used unit
2) re-routed the engine wire harness so that there was more slack on the ISC plug. I noticed that the wiring for the plug was very tight and pulling on the wires so I worries that might be causing issues.

So far I've only had the ISC buzz one time on me when the engine stalled but it was not the cause of the engine stalling. Otherwise it's been good and I've run an entire track weekend so plenty of heat and abuse. Keeping fingers crossed.