Noob needs ideas!

I'm tossing this out to the masses after searching for hours with no real solid clues.
My car is 1990 NA GTU 5 speed - 140K miles on car with about 30K on a rebuilt engine from a AT vert that we just installed a thousand miles ago.

We took our time and did everything as good as we could on the engine swap and were rewarded with a GREAT running car... For about 800 miles....

Then I winged the engine up to about 7000 rpm it popped - through the exhaust, busting the cat into pieces that clogged it up. THAT was an easy fix. My (now empty) cat rings like an old oil drum now!

Then the weird stuff started... It seemed like each time the fuel tank got down to below half the engine would not rev past 4500 - it would go mushy then hit a brick wall. Well after dealing with that for a week or so, I began to notice that the car ran fine (it would rev above 5 grand easily between shifts) that is... until it had been up to full temperature for about 15 minutes or so - then the brick wall at 4500 rpm started again. As I continue to drive the car and it warms up even more the rpm at which the engine will not rev past creep lower and lower - down to 3500 rpm at times! It's kinda hard to drive like that - but when it cools off again, she'll pull hard again - for only about the first 10 miles.

Dad and I thought "Fuel Pump or Filter" right away, but started consulting the board on this site too. We haven't run the ECU codes yet but after tons of reading, and some late night exploring we have more clues.

Fuel Filter has only 1000 miles on it - but we took it off and flushed it out then blew it and the fuel line out with 100 psi of air while we were at it.
We took the pump and pickup assembly out and... Yes the tank had some crap in it - but not too bad... so we cleaned it out as good as we could with a magnet. The baffle for the sump is intact and we totally cleaned out the fuel strainer sock too. We cleaned all the connections to the pump, level warning thermistor and gauge sending unit. The pump seemed to run fine - so we put it all back together, added a 20 oz bottle of gum-out injector cleaner and 10 gallons of fresh gasoline.

So... Did that 5 hours of work change ANYTHING? Hell NO !!!! - As soon as it warmed up, it took a dump at 4000 rpm - just as before.

Question to the rex-gurus here:

Are we chasing the wrong thing, or is my fuel pump just a tired old turd that gets hot and cant push enough fuel anymore - So I gotta replace it?

If a replacement pump seems like the most likely, what's the word on a recommended pump for a stock 1990 N/A engine - please consider my very limited high-school budget though.

Thanks for any ideas and help!

Sorry for the baZillion word post...

Redrocket1990

 

Sounds like a pump could be a likely culprit. Get one off the for sale section here, you can probably get one for very cheap.

 

Yeah man, if you do find it's the pump, just get another one from an NA in the 2nd gen parts section for dirt cheap.

 

Sounds like a typical series five car gone into limp mode. Pull the codes and I'll bet you find a OMP code there.

OMP goes bad...............car goes into limp mode after warming up and a short drive.

 

Thanks for the suggestion of buying a Pump from someone here - If I find out fosure it's the pump that's this first place I'll look.

Hailers, I pulled the codes and I had codes 12,18 (TPS) and 34 (Bypass air Control Valve)

Could either of those cause a "limp home mode?"

Also, on a discovery mission, I pulled the secondary injectors and the front one's green plastic pintle cover had broken, but most (if not all) of the pieces were laying down on the diffuser - I pulled the pieces out carefully. Also, the rear one's filter screen had a ton of dark brown, super fine crap in it - enough to coat the center of my hand when I turned it over and poured the fuel out of it. Luckily, I have a couple of spare injectors on hand from my old blown engine. I've cleaned the spare injectors by using carb cleaner and 45 psi of air injected into them as I pushed on the pintle with a small rod. I did this about 5 times fro each injector. They seem to blow clean with an even pattern. I'm installing them tonight and checking for leaks. Then I'll disconnect the battery to clear the codes and try starting her up again.

What does the BAC do that is vital?

 

Its unclear to me if the full and narrow range TPS are out of range that the car will go into limp mode.

That said, I'd fully warm up the engine and backprobe pins 2F and 2G and see if your meters reading match the FSM's figures. See CONTROL UNIT of the FUEL AND EMISSIONS SECTION of the FSM.

Narrow range, pin 2F should read approx 1vdc at idle and the Full range, pin 2G should read approx 0.8vdc at idle (fully hot engine idling). Leave all plugs on the ECU and either backprobe the wires at the plug or pin ***** the wires at those locations.

If out of range, then turn the TPS screw til the Narrow range reads one volt dc. That should take care of that.

If 2F or 2G read 4.5 to 5vdc, then most likely the wires are open bt the TPS and ECU. Not likely at all.

Then again, your fuel injectors etc sound crummy. Change the strainer on the end of the fuel pump along with the fuel filter.

 

Bahhhhh !!!

I'm getting frustrated here. We're 18 hours of investigative and back breaking work into this puzzle and we're getting shutdown every time! (Backbreaking from leaning over the engine and gas tank for hours.)

We worked on the car that is just laughing at our efforts last night till 1am.

Hailers, we did a static (engine not running, TPS disconnected) check of the TPS - using as a reference, the resistance values from the 1989 FSM that we found online - I hope it's close enough to the correct values for the TPS on my 1990 engine. Both pots were within range.

Next, we replaced both secondary injectors with good used injectors from another engine, cleaned out the secondary fuel rail and replaced (2nd time) the fuel filter as well. Checked for leaks and disconnected the battery to clear the codes then TRIED starting her up.... NOTHING. But, after cleaning up the plugs and clearing a flooded engine (That's the first time THAT has happened to me- but Dad knew what to do. It probably flooded from accidently forgetting the jumper wire was still in the connector from checking the injectors for leaks when we first tried to start it) We finally got it started and let it idle and warm up to full water temperature. We took the car out for a test drive and it ran great (revving clean up to 6500rpm) for about 3 or 4 minutes and then suddenly it started hitting that brick wall at approx 4000 rpm again!!!!!!!!

We drove it back to Dad's shop and checked for codes - the TPS codes were not present but the BAC code 34 was set again. Is THAT code supposed to cause the ECU to "Limp?" Okay Okay, we check the BAC valve according to the FSM next.

Hailers, since it was so late, we didn't back probe the TPS for the voltages that you wrote about yet - but we plan to. We should do this with the engine running right? And are the 2F and 2G terminals that you refer to also at the F and G terminals of the TPS connector? Or are you talking about checking at the ECU?

Why can't this be easier??? There's so many trees to bark up - we're both going nutz trying to pick the best place to look next

Could this whole problem be a weak fuel pump? That would make this much less difficult!

Dad thinks I should have picked a 75 Toyota Celica as my first car - I'm beginning to believe him.

Thank You.

 

Any old car will have problems, end of story.

 

Yeah I catch yer drift farberio... I'm just getting anxious to boot it again and have it RESPOND! Thanks for keeping me honest.

Love my Seven.

Gonna crank on it tonight some more.

LateAhh,
-Redrocket1990

 

F and G on the ECU. Jpg attached. Shows the pinouts of the ECU and the view is looking at the wire side of the connectors with the connectors on the ECU. All backprobing should be done with all plugs attached to the ECU.

Second jpg shows a page from CONTROL UNIT pages of the FUEL AND EMISSIONS section of the FSM. It gives values for each pin of the ECU.

Fand G can be read at the ECU either with or without the engine running. Key to just ON or at idle, makes no difference.

BAC can't cause your problem. It's just a idle control item and only idle.

Will this car drive over 4000 rpm if you gently apply pressure to the pedal? Like slowly accelerate past 4000 to over 5-6000rpm? IF you can do that, then the problem sounds like a secondary injectors not coming online when commanded.

Secondarys only come online if the ECU senses a LOAD and at the same time the rpm are over 3800 rpms. Sooooo, if a car is driven gently, no LOAD will be seen by the ECU and the engine will accelerate to over 5000rpm without the secondary injectors ever being commanded to ON.

 

Thank You to Hailers for clarifying your suggestion on how to check that the TPS was within range - and thanks too for the time it took to add the indicating notes to the pin-out on the ECU for us - That made it perfectly clear!

Here's what we found:

With no adjustment of the TPS (Pin 2F Idle) 1.5v
With no adjustment of the TPS (Pin 2F Full throt) 4.5v
With no adjustment of the TPS (Pin 2G Idle) .95v
With no adjustment of the TPS (Pin 2G Full throt) 4.5v

Narrow range adjusted at Locking Screw on TB shaft
Then:
Post adjust: (Pin 2F Idle) 1.0v
Post adjust: (Pin 2F Full throt) 4.5v (no Change)

We did not adjust the full range Pin (2G) because it was "close."

How do you adjust the Full range pot? Can the actuating cam on the throttle shaft be adjusted for position? We were afraid that after spending 30 minutes getting the Narrow range adjusted to spec we'd have to take off the adjusting levers for the narrow range pot to get to the cam (in order to see if it was even adjustable) It was late again and Dad & I were really tired so we didn't pull the narrow range levers off the shaft to investigate.

Do the above voltages seem within range? The FSM says "approx." Is 4.5vdc enough at full throttle? Neither pot (Narrow or Full) would allow any higher voltage at full throttle - even when pushed in all the way by hand.

It was raining hard at midnight - and to get the car out of the basement garage we have to drive over the already squishy grass from rain two days ago - so we didn't do a post adjustment road test of my car last night.

One thing we did find is that ECU block connector #3 had the keeper clip broken off. So the connector pulled out really easy - I'm wondering if the secondary injector actuating pins (3X & 3Z ?) were not making contact. My Dad says that when a block connector is about to fall out of any electronic device it's the side pins that usually brake contact first - and by the 3x & 3z pin-location along with the harness having to make a tight turn around the edge of the ECU right at that very location - it kinda sounds like a possibility huh?

Anyhoo, I guess our next step is to rig some LEDs to ascertain that power is getting to the secondaries under load.



- Red

 

The figures you gave for post adjustment of the TPS are good to go. As long as the engine was HOT when you did it and not COLD when you checked it. The HOT or COLD matters because of the water thermowax which MOVES the throttle linkage as it cools off and in turn that effects the setting of the TPS (set when the engine is HOT so that the water thermowax will have completley come off the roll pin).

I'm in favor of LEDs on the secondary injector wires at the ECU. Another way I used several yrs ago, was to backprobe the secondary injector wires with a digital meter, at the ECU and then go for a ride. The secondary wires will read alt voltage up and until the time you stomp on the pedal to put a load on the engine and reach over 3800rpm. At that point the alternator voltage will drop like a rock to ??? depends, usually in the 7-8vdc range as they are activated. Been there, done that a lot in the past for amusement. I"ve used LED lights also which work very well. Just remember that the injector wire will be the gnd for the LED and you have to find a source of power for the LED's other wire.

Secondary injectors batch fire so it would matter not if you got the fwd secondary injector plug put on rear secondary injector. And vice versa.

While your there, check the voltage of the boost/pressure sensor at idle and compare it to the Control Unit page.

Is this all stock wiring in the car? Best of your knowledge will do.

 

Craaaap! Hailers, You told us to do this test hot - but we forgot! We had started the car several times but it never got up to temp - we just plain glossed over your suggestion (requirement) to do test while the engine is hot.

Well, I foresee another TPS adjustment session coming up...

Even if it is still a muddy marsh in the back yard and we can't pull the car out, we have exhaust removal tubes in the shop with suction - so we can warm the engine to full (idle) operating temp - we'll just wait for the thermostat to open before we check it - about 10 minutes of idling ought to do it.

By the Way: The car is a N/A - not a turbo. So I don't think it has a pressure sensor.

Wiring is stock (but...) The transplanted engine was from a 1990 N/A automatic transmission convertible. It came with both drivers and passenger's side wiring harnesses delivered with the engine.

The original engine harness for my car had been hacked up by the idiot that owned the car before me.

When we replaced the engine, we decided to use the harnesses that came with the 1990 'vert engine - they were factory perfect... It had the optional airbag wiring within the passenger side wiring harness. We took the airbag wiring out - and re-bundled the harness. On the Driver's side engine harness, we took the auto-trans wiring out and subbed the manual trans wiring from my original 5 speed harness into it.

Dad used the FSM (from an 1989 S5) to rebuild them and to make certain that both sides were all correct and we then cleaned and tested every wire and connector. He's a recording engineer, so he's waaaay "****" with the wiring stuff....

Remember, this car worked/ran perfectly until I had been driving it for about a thousand miles. Then it started it's 4000 rpm Brick wall sh*t...

For the record - Front and Rear injector plugs ARE in the correct position.

We haven't checked continuity between the secondary injector plugs and terminal 3X and 3Z on the ECU though. And I guess all 4 injectors get their positive voltage from connectors on the trailing coil- I'll check the wiring continuity from the secondary plugs to BOTH places ASAP.

Thanks again for following my ramblings.

-RedRocket

 

No. If you pull the ECU plugs off and check each injector wire in the plug, with the key to ON, you should find batt voltage on each of the injector wires. This would PROVE the wiring to each injector plug is good by seeing the batt voltage on them.

Power for the injectors goes thru the Main Relay to each injector........passes thru each injectors coil, and ends up at the ECU plugs. The injectors work by the ECU pulsing a gnd on the injector wires.

Check the voltage at pin 2H for the pressure sensors output. All plugs connected to the ECU and key to ON. The figure you read should match the figure in the FSM ...Control Unit pages. IF not, then that might be the problem.

 

Man, NOTHING seems to be obviously wrong with this car! But it still falls flat at 3800-4000 rpm.

Hailers, on your suggestion, last night I checked and rechecked a bunch of things.

Pressure sensor is dead on perfect voltage at pin 2H (with and without vacuum applied.)

Sec Injector connectors (both wires on each connector) register batt voltage when the ignition is on.

Brought engine up to operating temp and rechecked the TPS adjustment - they are both is the same basic rage that they were yesterday.

The engine has been freshly grounded extremely well to the harnesses, chassis & firewall and the ECU frame has had all connections cleaned and dialectric grease put on all bolts holding it down... But just cause I could, I grabbed a length of huge #5 gauge stranded wire and grounded the ECU directly from the engine block to the mounting bolts of the ECU.

Nothing! I still has no power above 4000 rpm. If I coax it gingerly, the car will run 90 miles an hour and run past 5500 to 6000 rpm but thats with very little power and a really long straight away. I did notice this morning as I drove it - that in second or third gear - if I coax it past 4000 rpm and hold the throttle in position as it's stumbling and barely making that speed the secondarys cut on for a short moment but within a half second or so it stumbles and gets weak again.

I'm still thinking the fuel pump just cant keep up with the needs of the engine,and when a little fuel does make it up to the secondary rail - as the car is motoring down the road , it hits the injectors and blammo a little burst of power!

I see three options:

LEDS on the secondary output pins of the 'puter two ascertain that the injectors are truly firing.

Getting a fuel pressure gauge that will read high enough and check the pressure while driving. Could I "rig" an oil pressure gauge for this purpose?

Pop for a new fuel pump....

Any more suggestions. Anybody... Anybody... Bueler... Bueler...........

Thanks for all the help on this bitch of a problem guys!

Redrocket1990:

 

I think a oil pressure gauge will work. I'd make sure that when your though, that you drain all the fuel out of it 'cause after a extended period of time (months/yrs), it'll start reading bad. Just my opinion. I've even used a compression gauge in the past for this (eventually RUINED that sucker from too much abuse). Just tee it into the rubber line b/t the filter and the engine hard lines.

Fuel should be flowing continuously thru the rails back to the fuel tank when you jumper the yellow two socket fuel pump check connector. Jumper it and listen.

I'd NEVER buy another fuel pump unless I observed a problem with the one you have (use a fuel gauge/oil gauge). Should read approx 28-31 psi at idle and when ON IT should read 37-39spi (non turbo car). When I use a fuel gauge I tie it to my windshield wipers and go for a ride and start at it.

Again, don't read the secondary injector wires at the injector plug, read the voltage at the ECU plug with the plug off the ECU. It should show batt voltage proving the circuit to and from the injector plugs is good to go.

I'd put the LEDs on the secondary wires at the ECU and go for a ride or backprobe either of them with a digital meter and go for a ride and watch the voltage to see if it drops from 13-14vdc down to 7-8 vdc when you GET ON IT above 3800rpms. LEds won't flash but will glow ON when you over 3800rpm.

 

Wow! It has been a crazy week. So sorry to act all disappeared and all - Huge school project and waiting for a part prevented much progress in the last few days.

Hailers, The compression gauge told the story!!!! We built a bracket like you suggested and using about 6 brass fittings adapted the comp. gauge to tee off, post fuel filter. We then went for a drive about midnight friday night with Dad holding a mini-mag flashlight focused through the windshield on the compression tester masquerading as a fuel pressure gauge.

Idle and cruise pressure was about 35psi - but when I got into it the pressure did EXACTLY opposite of what it should - it went down... So far down that it was just about zero psi for a moment. As soon as I let out of it, or just held the throttle steady, it would attempt a recovery and the engine would kinda accelerate and drop off within a second - as the fuel psi dropped down again.

We turned around and crept home... We didn't want to lean it out anymore than it took to diagnose a major fuel feed problem.

We we ordered a new pump (Bosch) and filter screen. It came in today - but I don't get paid till tomorrow... We'll replace it tomorrow night.

While we were waiting for the pump, we have cleaned, de-rustified and "RedKoted" the tank. That was a bit of a pain, but I think the coating took real well and I'll be running fuel that is not BROWN through my injectors soon.

I sure hope this cures my car of its weak-*** performance. Can't wait to find out!

 

If you want to test it to be sure it's a fuel pump, I have one you can throw on there and see if thats the problem. That way if its not, you can return the new one. I live in Pleasant Hill.

 

Wow... Life is good again!

First of all, Thank you so much to Hailers for hangin' with us throughout this ordeal and passing out a ton of really good suggestions. And thank you to a nearby Rotor Head, baughb'smx6 for offering a fuel pump to try before I spent an entire week's worth of cash on a new one. (It was a special order from NAPA on 7hwy, so they required me to lay down 1/2 of the money before they'd even order it for me - so I was pretty much into a new pump anyway) Again, thanks for the offer though. Finally, I am so glad this forum exists - I never, I repeat NEVER would have put my blown engine heap on the road with out all of your help! This depth of the info available at the search function key is amazing!

Okay here's the final chapter. IT WAS THE FUEL PUMP ALL ALONG!!!!! Dad and I were attempting to chase any and all problems that didn't cost money first - and that, by the way, is where Hailers and his experience with our cars came in so welcome.

Gawd, I've learned a lot in the last couple of weeks! Found several problems I didn't know existed (but would have kicked my car to the curb eventually - they were a Broken tip on a secondary injector, and a way rusty fuel tank that needed attention NOW) and learned the frustration and rewards of trouble shooting and finally that tenacity really pays off. Also I learned tonight that my ol' Dad can throw a kick-*** power shift!!!! He test drove the car with the new pump tonight (with me holding the mag-light on the fuel gauge) and got second and third gear scratch - a good solid bark in third as he went through the gears shifting at about 7 grand too! I had no idea he could (or would) do that in front of me - I think he actually was havin' fun. Me too...

Till next time,
To infinity and beyond! Redrocket out!