North American Turbocoupe Organization



Diagnostics help
Walsted Offline
Posting Freak
#1
The car has been intermittently hesitating on me. If I floor it to get on the road, it acts like its not advancing timing until I get up to about 5psi, and then it takes off and jolts my head back into the seat. If I'm accerating to highway speed, it is scary, and I get my head jerked four times on my way to fifth gear. It does it more when it is hot outside than when it is cool.

Pulled codes, no KOEO, CM was 27, 41, 42, so I adjusted and tested the TPS, and it would stall out during KOER. Timing is at 10 without SPOUT, 27 with SPOUT. FPR didn't seem to be leaking when I sucked on the vacuum line.

Outside air temp was about 105F when I ran codes, and air density was equivalent to 6000 feet at standard atmosphere. Does that make a difference?

Any suggestions on what else to check?

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Mike Walsted - NATO member
1986 5-speed TurboCoupe with a few upgrades.
Mike Walsted - Sold my 1986 5-speed TurboCoupe
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trashline Offline
Posting Freak
#2
hmm not to scare you but sounds like my car when it blew the HG. and it also sounds like my car when it gets below a 1/4 tank of gas

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1966 mustang
1988 tbird
Brian

www.BCPCustom.com

06 Cobalt SS
66 mustang 289 C4 handfully modded

Stingers IC install and tbird photos
http://community.webshots.com/user/trashline
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Walsted Offline
Posting Freak
#3
Full tank of gas, no oil in the water, no water in the oil.

I am leaning away from head gasket at the moment, since the problem goes away under boost. I am also leaning away from a fuel system problem, since the gas used matches what the tripminder says I used. Gas mileage is about 2 mpg lower than usual.

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Mike Walsted - NATO member
1986 5-speed TurboCoupe with a few upgrades.
Mike Walsted - Sold my 1986 5-speed TurboCoupe
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Joe F Offline
Posting Freak
#4
Have you checked your fuel pressure? maybe there's a problem there with delivery. Just a thought.

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Joe F.
JR's Place - My 87 TC
JR's Place - My '87 Turbocoupe
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JT Offline
Posting Freak
#5
You have the upgraded LA2/3 EEC in your '86, right? Code 27 is a VSS (vehicle speed sensor) sensor/circuit issue.

Having both rich and lean CM codes would point to a possible o2 sensor circuit issue or possible a VAF issue. It would not be limited to that, though.
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Walsted Offline
Posting Freak
#6
Yes, I'm running the LA3. I had a mental malfunction and thought VSS=TPS. Obviously wrong. I'll check the VSS wiring tomorrow.

I'm doubting fuel pressure is a problem, since I've gone through two tanks of gas and the tripminder fuel used matches the amount on the pump.

Haven't checked the VAF, yet. Thanks. That will be done tomorrow as well. I didn't see the methodology in the FAQs or tech articles - does anyone know off the top of their head which two wires need to be probed to check for voltage values?

Thanks for the help.

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Mike Walsted - NATO member
1986 5-speed TurboCoupe with a few upgrades.
Mike Walsted - Sold my 1986 5-speed TurboCoupe
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Jeff K Offline
Administrator
#7
VAF wires: BK/W = SIG RETURN, W/BK = VAF output. When I suspect a problem with the VAF, TPS, etc, I will tap into the circuit, and run a long pair of wires to the cabin so I can monitor the suspect components output while driving.



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Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 23 psi, forced air intercooler, water injection, bypass valve, Ranger roller cam, subframes, etc., etc.. // 86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP nitrous, ignition, gears, suspension, etc., etc.... // 91 Escort: Bone stock winter car // 04 Taurus Duratec (wifes car) // 91 Topaz (daughters first car)
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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Joe F Offline
Posting Freak
#8
How exactly does the tripminder work? Does the ECM "tell" it how much gas has been metered to the engine? If so, IMHO you still might have a fuel delivery problem, but I've been wrong before. Good luck!

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Joe F.
JR's Place - My 87 TC
JR's Place - My '87 Turbocoupe
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Jeff K Offline
Administrator
#9
Quite true, Joe, a fuel pressure test is THE way to rule in / rule out fuel system problems. Just because the MPG indicared by the tripminder is reasonable really doesnt provide any useful info.

Tripminder gets fuel used info via the DOL (data output link) from the EEC. EEC measures fuel consumption based on injector pulse width, and knowing the injector flow rate, and assuming fuel pressure is near stock 39 psi base, so the injectors flow their stock lbs/hr. Tripminder gets updated roughly once per second on fuel use for the instantaneous MPG feature, and tripminder basically integrates total fuel used over time since last reset to calculate average MPG. Of course, tripminder gets distance traveled and speed input from the VSS.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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JT Offline
Posting Freak
#10
Possibly could be fuel delivery issue, but when you have both lean and rich codes stored, looking at the VAF's input and o2 sensor/circuit is the top 2 on the list for a condition like this. However, as i mentioned and acknowledged, it is not limited to just those 2 things and it could be a fuel issue. Just in my experience, a fuel delivery issue is more likely to give you one side or the other.

But it's not best to rule things out unless tested, so i wouldn't rule out fuel delivery either. Good luck.
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