**Updated in 'Reply' - Possibly MAF?**

Symptoms:
-Driving down road at constant throttle it feels like it is cutting out intermittently.
-While vehicle is moving or idling less than 2 minutes, the engine races @ 1500 -1900.
-After idling for a minute or two, the idle repeatedly drops right to the point of stalling then picks up a bit.
-Eventually stalls.

Notes:
No codes
No EGR, AIR, or Cat
52mm TB, Ported Plenum, Headers, & Corsas
New ECM, Street Chip, IAC, and MAF Burnoff Module (Injector Control Relay)
I can feel the injectors firing and they ohmed out cold last tank.
Fuel pressure was normal and adjustable last tank.

Ideas?

I plan to verify that the TPS is still set properly and that the IAC ohms out.

 

TPS: .54v - 4.6v - Check
IAC: 0 Ohms, 0 Ohms, Infinite, Infinite - Check
MAF Connector (MAF not connected): 12v Power, 5v signal (should be .5.?), 0v Burn or Analog - Check(?)

Disconnected MAF and started. Idled PERFECTLY. Threw a Code 33 (MAF signal voltage out of range - Probably high) Ummm... Sounds like a MAF problem, but I am concerned about getting a high signal with no MAF connected and getting a 5v signal from the ECM to the MAF connector.

Thoughts?

MAF FUBAR?

 

I still say vacuum leak.

 

I suppose that having a steady idle with the MAF off would be a good time to do the carb-cleaner/propane-torch test.

Tomorrow. I'm tired! Just adjusted the throttle and tore down my lawnmower. Much better run!

 

I don't know if runnin' w/o the maf plugged in will give you a steady idle. I would still crank it up to 1100 rpm's, just to make sure.

 

Would a vacuum leak cause the brief cut in power at cruise?

Interesting:
I plugged the bypass port between the TB butterflies with my finger. Good suction. No change in idle. (Obviously the MAF was off.)

 

I don't think a leak in the intake would affect rpms at speed at all. That bothers me.

 

Intake/vacuum leak also should NOT drive idle up to 1500 - 1900 either.

'Cutting out' doesn't sound like a leaky intake.

No codes (if all electrics are functioning properly), is a dead ringer for the intake leak. I would focus on that first, and see what goes after that.

 

Not so much a cut-out (like a non-fire) as a dip in power (like the throttle was jumpy).

I'll double check everything, but a very respected tuner looked for a couple hours and found no leak. He did the spray and the torch method. I'll check about in the morning.

If I find nothing, what are we thinking next?
Ohm injectors warm? I feel each one gets a pulse @ idle, but maybe they're not firing well?
I wish I had an analog volt meter to check the IAC pulses.
Pinch vacuum lines after each connection?
Could be a worn purge valve?
Rattle in the TPS?

 

How's the temps? Faulty fuel delivery at speed might make for a leaner burn, and possibly higher runnin' temps.

He might be a better tuner than us all, but if he didn't get the high steady idle first, it's hard to say 'NO leak'.


Next? I don't think spark, since you're sayin' no 'miss' at speed. That just sounds like air. No EGR, no AIR could be the problem.

Fuel? Dunno'. Besides fuel pressure check... You have checked at idle with vacuum, at idle without vacuum (FPR disconnected), and pedal down pressure on the highway, with a long connector on the pressure guage, and taped to the windshield???

 

fuel pressure testing...

 

With the 160 stat and chip, I have a steady coolant temp of 165 at cruise. Oil rarely breaks 200 and only when I'm having a little 'fun.'

For a while, he thought it was shrinking harness wire insulation at the relays. It used to 'surge and dump' wildly then stall. Tinkering with those wires seemed to stop it. The high idle happenned after a hiway trip and would only stop if I jumped on the gas pedal for a couple seconds. Removing the EGR seemed to work. It has been running great for a couple months. Now this...

Is it possible that I have fluctuating fuel pressure? I wonder if too much pressure was causing too much fuel and keeping the idle high until a stomp reset the AFPR? Low idle might be causing a starvation? The low idle happens after the high idle situation, which might be the fuel rail going from too high pressure to too low pressure... Cold starts are perfect. Prime for 2 seconds, turn the key, and BAM! It on and eager.

Hmmm... To the tester!

 

My mustang was doing the same thing. Replaced the MAF and good as new.

 

OK. More info.

Fuel Pressure (PSI):
Prime - 42
Cold Idle - 40 Vac On, 45 Vac Off
WOT - 46
Warm Idle - 36 Vac On, Right after run
Seems Normal

Leakdown (Minutes - PSI)
0 - 44
2 - 44
8 - 40
10 - 38
14 - 32
18 - 26
20 - 24
Seems Normal

Removed belt. All pulleys spin normally. No catching.
Car runs worst when fan comes on.
Pulled 2 plugs. Look clean. A little fuel on the threads.

Drive:
At low throttle/cruise, there were intermittent times of a dip in power.
At stops, engine varied from racing @ 1900 to 500 and trying to stall out.
Mild acceleration caused dip in power, sporatic as always.
Car stalled while backing into garage - CODE.
3 times a restart failed immediately. Restart with throttle kept it running.

Code 34 - MAF issue. Signal voltage probably too low.
That makes a code 33 with MAF disconnected and a 34 with MAF connected. Wires in tact. 'Ford Test' inconclusive.

Ohmed MAF:
AB - Infinite
AC - 14.5
AD - Infinite
AE - 4.5
Normal? I have no idea.

I have a HyperCrap MAF I might try, but it undersenses airflow and causes problems. (Bad design according to my tuner).

 

Runs worse when the fan comes on. ...
Because of the electrical draw? Or because of the temp that it has reached? Neither one jibes with maf/air problem...

Good fuel pressure at WOT HAS TO be an air mis-measurement - maf.

Google your maf ohm specs, before you drop cash...

 

MAF test; I don;t think it applies here tho', but give it a read over...


On second thought, a regular vacuum leak causes only idle problems, whereas this thing says failed MAF causes ALSO driveability problems ???

 

OK Get this:

Put in a HyperTech MAF I had on the shelf. Idle and driveability SOLVED.

Go for a hiway drive:
When I return to side streets, idle is @ 1700 until I put it in reverse, back into the garage. Then normal. Drive on the highway and the idle is high, again. What the heck?

FYI:
While I let the new MAF idle for a few minutes, I checked the old MAF.
AB - Infinite
AC - 17 hot, 14.5 cold
AD - Infinite
AE - 4.5 cold, 8.5 hot
That can't be right.

 

Vibration? Heat? Is it possible that the wires run in the same bundle and have rubbed together enough to cause a leakage?

 

Well, you're 100% sure it runs worse when the fan comes on?

If so, fire it up again with the fan disconnected, and watch the guage to see if the quality changes @ the fan trigger temperature.

If it stays the same, it's a power draw problem (again, IF it really does get worse EVERY TIME the fan trips on).




jibes = goes along with / indicates the same problem, as opposed to indicates a DIFFERENT problem.

 

With the other MAF, it was instantaneous. Fan comes on and the idle started dipping & fluctuating until it stalled. This MAF has not experienced this, yet. I'll go give it a try in a few.

If it does misbehave with the fan disconnected, what should I look at to fix? What if it doesn't? Is it probable that wires are getting leakage onto each other? Where would this be?