I'm out of ideas on this one...

I bought the car without any HVAC installed and over the past week reinstalled all the HVAC components (blower, AC core and heater core/main control). I also installed stock heater lines. Everything works great with the car sitting still, but it drives slightly bogged down and has significant hesitation at 3.5-4k (boost seems fine). My fuel pump died a few months ago and the car drove the exact same way. Since the pump is only two months old, I feel that I screwed up something electrical and now the fuel pump isn't getting proper voltage (stock wiring). But, it could be something different entirely.

I've checked and rechecked everything, mainly focusing on electrical connections and grounds. Do you guys have any ideas?

 

I figured I must have disconnected/broke something when I added the heater hoses, but nothing stands out at this point. I just checked the ignition and replaced the plug wires, no change. I also bypassed my twin power, still no change.

One more symptom that's leading me to believe it's electrical... When the lights are on, I'm getting an intermittent buzzing sound coming from the drivers side rear speaker. It only seems to come on after a minute or two of driving, then it's essentially constant. It's pretty loud.

Is there any interior wiring that, when screwed up, could cause the car to hesitate badly? Such an annoying issue, there's only 6 plugs that connect to the dash, it's kind of hard to mess them up.

 

First you have to go over all the areas where you were working and look for mess-ups.

Verify that the fuel pump speed relay circuit is OK by checking the voltage at the fuel pump at normal idle. I think it is about 9 volts?? Then pull the speed relay and put a jumper across the back 2 contacts (towards the engine). This should give above 11vdc.

If that works you then can do a similar test but when driving to insure the speed relay is being activated.

 

When I read the post title my first thought was "ground wires". Check your grounds, especially the one right there at the ECU.

 

Thanks guys... I felt it was the grounds too. I checked all them initially, but I'll look again around the ecu.

cewrx7r1, that's a good test. I'll give it a try. Can you be more specific which contacts to jump at the speed relay? Thanks.

 

You need to learn how to use the FSM!

 

yea bro find the vac hose tha runs to the firewall and plug it off at manifold and c if hesitation goes away if so vac hose loose inside someware

 

Looks like I should jump C & D, right?

 

Yep. Jump those and you will bypass the fuel pump resistor.

Steve

 

See, that was not hard!
We original owners only had the FSM and similar manuals to learn from.

Then check and verify that the map sensor has the vacuum/boost hose connected to it.

 

I agree that you probably have a problem with the current going to the fuel pump so hopefully it's just the resistor and if you need one let me know.

If it's not the resistor I'd lean toward some aftermarket electronic part added to the car and go from there. Things like stereo equipment, alarms, electric locks etc....

 

Nope, not hard, I was just being lazy . Thanks for the suggestion to jump the terminals, I didn't think of that at all. Map Sensor is definitely connected. I'm pretty confident that everything I can visually check has been checked 5 times .

Fritz, thanks. The car has no aftermarket electronics besides a boost gauge and pfc. Although the stock stereo is totally shot, maybe I should just unplug it completely...

I'll test the resister as well as the fp circuit and see where that leads.

 

Minor update - I searched around tonight and found an unplugged connector that I missed. It's under the drivers side dash behind the side kick-panel (in front of the left foot rest). It was shoved into the hole that leads to the fender harness pass-through.

I don't see anywhere that it connects to, do you guys know what it is?



Also, my relay box is under my V-Mount and a complete bitch to get to. So I unbolted a things on the V-mount and got it out. I re-tested the FP speed relay and it clicked and help held continuity through a voltmeter with no issues. However, the TNS relay has something rattling around in it, so I'll replace that. I'll jump the circuit to check FP voltage tomorrow when the wife and kids are awake...

 

Did some more testing... any feedback is helpful at this point:

1) At idle my voltage to the pump is ~6.8 volts, when I jump the Fuel Pump Speed Relay it goes up to 11.00 flat. I'm not sure what these should be, but that seems a little low (was expecting ~9 and ~12)

2) The resistance of the Fuel Pump Resistor is .6 ohms and is in spec.

3) I tested the connectivity from pin 1K at the ECU to the Fuel Pump Speed Relay and they connect fine (see below Z-28 from the electric manual for reference).

4) I inspected the pins and opened up the PFC ECU and saw nothing unusual.

5) I did the test on F-100; jumped GND and F/P and turned on the ignition. The Manual says I should see battery positive voltage at the pump, but I see ~5.8 volts. Looking at the diagram below, it looks like this wouldn't close the Speed Relay. Since the resistor is in the loop, I shouldn't see Battery positive voltage, but something less. Am I misinterpreting the manual (pic also attached)?

 

Hi Matt,

looks like your mystery plugs is for CPU2, for the flashers and hazard lights:



The unit is located tucked back behind that mess of wires, perpendicular to the dead pedal and back a bit towards the door.

 

Thanks Rich! I'll take a closer look, but the flashers work fine, does that make sense?

At this point, I'm just going to rewire the pump. At least I can debug these problems more easily than tracing down issues with the ignition system (and I really don't care if there are issues given that everything else seems to work fine). I'll probably upgrade the alternator too at this point. I don't want to deal with electrical issues any more, they are a pain in the ***.

One question on the fuel pump rewire, though - can I just jump the Speed Relay slot (terminal C & D) in the relay box and reuse the stock speed relay for the rewire? In searching, no one seems to mention anything about bypassing the stock speed relay...

 

I rewired the fuel pump using the Dale Clark method (wired the main fuel pump relay to the battery) plus added an additional 10 gauge ground. The voltage with the resistor in the loop at idle went up from 6.8 volts to 7.6 volts and with the speed relay jumped it went from 11.00 to 13.00 volts at idle. So there was a definite improvement there.

Went for a drive and nothing changed... As soon as I hit 3300 RPMs with boost, I get a massive hesitation, then just doesn't want to do anything by 4k. I then jumped the speed relay thinking that the ECU just wasn't grounding it under load; again no change.

I'm going nuts on this issue. Is it possible that my 150 mile, 2 month old, supra pump failed or am I just focusing on the wrong problem? I also have to assume that this has nothing to do with the dash at this point and is likely a coincidence.

 

Is that when your secondary injectors are supposed to come on? If so, then maybe they aren't, or only one is.

 

Yes, it's likely when they come on. There's more background on this. I had this exact same issue back in the fall (Oct 2012). I tested everything then including both injectors (I applied 9 volts to to the ecu harness pins and they both snapped open). Also they only have about 500 miles since being flow tested and cleaned. Out of ideas, i replaced the fuel pump and everything worked perfectly.

The car got tuned and drove amazing. Then it sat for for about 6 weeks due to winter (i idled it here and there). Then i added HVAC and heater lines and the issue is back.

 

One more symptom to call out, when I jumped the speed relay at idle, the voltage went up to 13 volts, but the fuel pressure was at a constant 38 psi. Shouldn't it have gone up?

 

Sounds like the car is going into limp mode

As soon as you try to boost it falls flat on it's face (no boost and can't rev past 4500 or so) and you can't accelerate correct?

Did you plug the plug back into the CPU #2 I don't think the car will go into limp mode with that unplugged but it couldn't hurt to plug it back in.

Are you using a PFC? If you are I don't think the car will even go into limp mode.

Check the ECU connectors to be sure all the pins are pushed forward or making could contact with the ECU and anything else that could be disconnected etc.....

Check the knock sensor and OMP connections. Basically any connection that could cause limp mode.

 

With no boost, I can rev freely and go well past 4k in second gear. As soon as boost hits, the hesitation starts. I keep thinking a soon as boost hits, the secondary injectors open and the pump can't keep up. Also, the car makes boost fine. The pins on the pfc are all good and clean and straight. I could be wrong, but I don't think the PFC has a limp mode.

Also, that black plug doesn't go to the CPU #2, both plugs were in there and looked good. The black plug only has a 3" reach, and barely reaches the CPU #2 as well. Maybe it's for a touring (sunroof) or something?

The knock sensor is a great thing to check that I haven't looked at yet, I visually checked it, but that's it. What are the symptoms of a bad knock sensor?

 

As mentioned if you have a PFC I don't think limp mode is a question at all.

I'll check that plug on one of my cars when I get home later today if someone hasn't already checked it out.

Did you check the spark plugs?

 

Knock sensor wont do it. I have a buddy that road races an FD w PFC with it disconnected

Sorry for the false diagnosis, It's tough to tell in the pics without being there. If you reach the end of your rope, I know of an 'ok' FD shop in north-central NJ

 

So the knock sensor was plugged into the PS plug (PS removed)... I connected it properly and (as expected) nothing changed. I also visually inspected the Fuel Pump and all the connections looked good as did the o-ring.