Trying to diagnose what seems to be a fuel delivery issue

[davidlkirby]

I'll start out by saying I don't have a lot of mechanical experience working on cars. I've been driving my 87 7mgte for 9 years now, and my do-it-yourself list of accomplishments is: starter, alternator, radiator.

This car has been very reliable for me, I run the boost at a conservative 9lbs with a 3inch exhaust and thats it.

Lately, I've been experiencing an issue that starts when I run WOT. It's starts out with what feels like blips in the power curve above 4k rpm Once I feel that, the next pull drops power somewhere after 4k. I have a lot of experience with fuel cut when the turbo is too high, that cut is jerky and violent. This is not the same. It feels like someone has pulled my foot off the pedal when I haven't. To be sure, it happens when I run the turbo at 6lbs too. Also want to mention that building boost feels normal. It doesn't feel like a boost leak, which I've experienced years before. After this has happened at WOT, I experience this same rpm drop off even when accelerating at 2-3 rpm just to get to 30mph. I've been able to make it home, fortunately.

On a separate drive, I drove like a granny for 30 minutes and never had an issue.

I've tried searching for what this might be.
Fuel filter too old and clogged to deliver enough fuel at high rpm?
Is there a 2nd (high speed) relay for the fuel pump that might be bad?
Problems with AFM, how could I go about knowing?

Any ideas or suggestions? I think I need to go to a shop for this and would like to guide them as much as I can.

Thanks so much.

 

[ghostmkiiiturbo]

Check your CPS wires/connector.

 

[ghostmkiiiturbo]

Edit: That was vague.

CPS = cam position sensor

Its on the left side of the engine(facing toward the front of the car.) Behind the water neck.(Where the upper Radiator hose goes on the engine).

Also check your engine codes to see if anything is stored up if so post the codes here. If you need to know how to check codes, look under the EFI fuel injection section of the TSRM.

 

[davidlkirby]

Thanks for the clarification, ghost.

I connected and disconnected the wire harness for the CPS. Everything looked in order, no suspicious looking wires and the connector still snaps in place correctly.

I don't have the check engine light on to indicate codes, but just to be sure, I shorted the diagnostic pins and confirmed that the light flashed on and off evenly to indicate 'normal'.

Still think I should suspect CPS? Would I be able to drive it like grandma just fine (always starts perfectly) if it was a problem?

 

[BryanDyer]

How old are the plugs/wires/coils. Maybe you could possibly be getting ignition break up in the higher rpms when under load.

 

[ghostmkiiiturbo]

Probably not the cps then. Like bryan said Δ I think its an ignition/timing issue. Have you noticed a difference I fuel consumptionsince the issue started?

 

[davidlkirby]

Bryan, those items aren't newer than 9 years, and not more than 50k miles on them. Do you think that the 'ignition breakup' would trigger the computer to cut off the engine the way I described without throwing a check engine light?

Ghost, since this car isn't my daily driver, I didn't want to get stranded if it was something to do with a clogged fuel filter or dying pump. I took it out twice with hard driving to experience the issue and 30 minutes gently to a shop (who didnt have anyone with the expertise to diagnose) then home. I don't know how much gas consumption may have changed, but the car seems like if drives normal when driven gently.

I'll see if I can make a video.

I found another shop who may have someone with the experience to help me fix it. Should I ask them to change my plugs, wires and coils to start?

 

[ghostmkiiiturbo]

You can replace the plugs and wires relatively easy with no experience if you have the tools. I recommend ngk plugs and wires. The coils can be tested with a multimseter(or just an ohm meter) can get a cheap one at harbor freight $5 or so. The #6 plug is the worse to get to. Use the tsrm for the procedurs and acceptable range for texting the coils.

Your issue is mainly at WOT or when accelerating hard. Does the car jerk or kind of stjtter/shake like your not getting enough fuel?

 

[ghostmkiiiturbo]

You can replace the plugs and wires relatively easy with no experience if you have the tools. I recommend ngk plugs and wires. The coils can be tested with a multimseter(or just an ohm meter) can get a cheap one at harbor freight $5 or so. The #6 plug is the worse to get to. Use the tsrm for the procedurs and acceptable range for texting the coils.

Your issue is mainly at WOT or when accelerating hard. Does the car jerk or kind of stjtter/shake like your not getting enough fuel?

 

[super51fan]

I agree you shpuld repalce your plugs and plug wires first. Normal wear items. Good luck.

 

[Nick M]

Do you think that the 'ignition breakup' would trigger the computer to cut off the engine the way I described without throwing a check engine light?

No. And that is a very unlikely problem. Some here comment on it, but are/were likely wrong. There is a reason the mixture under boost form the factory is 9.5:1. Pull codes. Enrichment is a much more likely issue than ignition break up.

 

[supraguy@aol]

He said he had no codes. But i agree that afr is more likely the issue, especially if the power just subsides, rather than becomes a jerking or shaking.
You didn't mention the mileage of the motor. Has the filter or pump ever been replaced under your ownership?

 

[davidlkirby]

215k on body. Probably 150k on engine. About 70k since last head job in 2003. Don't think filter or pump has been touched on this body at least not since 2000. The power loss doesn't feel jerky. It feels like the engine gets shut off for a split second. Will get a video up tonight

 

[davidlkirby]

Thanks for your patience and input everyone. I got a video uploaded to youtube and paid closer attention to what was happening. The sound is pretty decent as long you're using headphones.

Heres the video:
http://www.youtube.com/watch?v=x7vGDasJNSQ

Description of whats happing during the video:
This is after a 5 minute drive keeping the rpm low. Engine warmed and acting normal so far.
At 30 seconds, I'm downshifted into 2nd at 30mpg and give it full throttle. At 35 seconds the car stops pulling for me and I keep the throttle fully open until 40.

I try another attempt at 2nd gear, this time the car gives out at 3k rpm (46 seconds) and I continue to hold the throttle down until 53 seconds with no response.

Suggestions and input much appreciated.

 

[stew_7mgte]

Been a while since i have posted on the forums but after watching the video i have never seen that before. I personally would check fuel pressure. try the 12v relay mod to the fuel pump or even better pull the fuel line at the rail route it into a container. then jumper the fuel pump from the diagnostic block. The spec for how much fuel should flow is in the tsrm. That will tell you if theres a problem with fuel delivery. Also maybe check your accelerator pedal. Have someone push the gas pedal down all the way and you watch the throttle plate so make sure its opening all the way. I have had some worn out / stretching cables do some weird things.

 

[davidlkirby]

Thanks for replying, stew. I feel very confident in the physical operation of my throttle linkage and plate, but I will keep it in mind and check it.

In an attempt to rule out my TPS, I disconnected it and my battery overnight. Left the TPS disconnected and drove again and had the same results. (except now it idles at 1k instead of 600) Do you think that rules out my TPS?

Tonight had an interesting twist, car gave out like it did on the video 2-3 times. I turn onto a side street and after I'm turned around and pull back onto the road, my car stalls out on my as I hit the gas from a stop. I tried to crank several times and couldn't start it. There was plenty of battery juice and the engine kept turning over and over. After taking a break and contemplating how I will tow it home, (5 minutes) it starts after 2 seconds of cranking and I drive home as safely as possible.

EDIT: I don't think it was my disconnected TPS that cause my car to stall in this case. In previous years, I've had the connector be faulty resulting in driving it for months disconnected without ever having such an issue.

I think checking the fuel pressure should be my next step, too. In the TRSM fi-73, I only see the pressure there should be and not the quantity of fuel that should flow. Does anyone have experience hooking up a fuel pressure gauge where the cold start injector is? Do I need the specific SST for that or can I grab something that will work at autozone?

Thanks for your input

 

[davidlkirby]

CONCLUSION: FAULTY FUEL RELAY!

After looking over the TSRM and searching the forums, I decided to hook up a multimeter to my fuel pump to read the voltage during this issue. I had read about the 2 voltage modes this car uses, 9 for low and 12 for high. After connecting a wire from the 'Fp' bank in the diagnosis box to my multimeter, I was able to drive and see the voltage:

http://www.youtube.com/watch?v=wXRb42Z6VOg

As you can see, my fuel pump voltage never goes over 9.5 volts! First suspect is the fuel pump relay, which controls whether power to the fuel pump gets sent through a resistor. I was able to follow these simple continuity tests found in the TSRM page FI-114

http://cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&P=114

Test A. a. on that page failed, my relay would not pass power to 'FP' which is the 12v line to the fuel pump.
Test A. b,c and B. a,b,c passed.

With nothing to lose on my broken relay, i pulled it open and discovered that the spring had popped off it's position! I put it back in place, reconnected the relay and now I'm driving will full power through all my gears!

Relay with spring back in it's correct position:

Thanks to all for the help and suggestions, it's much appreciated. Hopefully this will help someone experiencing similar behavior in the future.

 

[supraguy@aol]

Nice deductive work. Most people just keep replacing parts till they A) get lucky, or B) run out of money and sell it.
Never heard of that issue before, either.

And PS- Thank you for posting your remedy.
MANY people begin threads, where possible causes and solutions are tossed around by helpful members, and when the person resolves the issue, he goes on his merry way without posting the cure, since he doesn't 'need the forum's help' anymore. Posting the solution makes this thread useful to the next person that may need to correct his fuel issue, rather than a dead end.

 

[super51fan]

^^ Thanks for showing us what you found.