1adzam

87 GXL...

I've been chasing down a problem with my rebuild for weeks now with no luck in solving it. The problem is with a gradual increase of throttle to about 3300 rpm's the engine loses power and sounds like it's sucking for air. The port actuators retract at 3300 but if I go any further on the throttle they disengage because of the rpm drop.

The same thing happens if I go to about 3/4 throttle all at once however the rpm's will only hit about 1500.

I've checked for vac leaks, re-timed it about 4 times, made a ECU checker.. all fine no codes, checked AFM (replaced but no difference), grounded the beast to the point where I'm afraid to drive in an electrical storm. Checked compression which is 95 on the front and 101 on the rear. This is a new rebuild with about 8 hours of run time. The car idles perfectly at 800 rpm's and has no problem with a gradual increase in the throttle until about 3300 rpm's

Now it seems I lose power just about the point where the TPS is fully extended. As a matter of fact the same symptom will occur if I'm at 3300 rpm's after a gradual increase in throttle and push the TPS back in by hand. I checked the TPS with my code checker and adjusted until only one light is lit. What should I be checking next???? Could this be a mixture problem (seems to run rich)? Possible fuel delivery problem? (I need to get a fuel pressure gauge to check that), TPS issue? I'm at a loss and so is my car When do the secondaries kick in? Could they be a problem? Any ideas are appreciated!!!

black_sunshine

Check your TPS. Use a multimeter and make certain it's within specs.

A fresh rebuild will run oddly until it's broke-in. Why are you taking it over 4k when it's not broken-in yet (at least 500mi)? Patience is key....

Also, check the BACV. It's on the driver's side of the dynamic chamber. While you're at it, make sure the AWS solenoid (big air hoses to back of dynamic chamber; driver's side) is functioning and that you've got the two vacuum lines on the throttle-body between the firewall are connected, the three on the front of the throttle body between the alternator, the one on the back of the dynamic chamber, the two on the LIM that go to the air-control valve, and that single one on the LIM hidden under the primary injectors hooked-up. Make sure all the sensors are hooked-up; the water-temp sensor on the water-pump housing, the water-temp sensor under the oil-filter, the oil-pressure sender unit under the oil-filter, the air-temp sensor on the driver's side of the plenum (dynamic chamber), the AFM, the TPS, all the solenoids are hooked-up correctly and the two connectors on the oil-pan.

The secondaries should kick-in at around 3500, +/- 500 rpm. Sometimes later, sometimes sooner. I say these are most likely your problem. If you've grounded the hell out of everything, it's time to re-solder the ECU or get a replacment.

the TPS should illuminate both lights on the tester. You should be able to push the throttle down (in the engine bay) about 1/16 of an inch and have one turn off (along with a click of the appropriate solenoid), and then a little further and the other light turns off, along with the click of another solenoid.

Change your spark-plugs. Replace that O2 sensor. Anything else, and I'm out of ideas! Hope this helps.

Matt

1adzam

Thanks Matt. Most everything you've outlined here I have tried. I tried a new ECU but that didn't help. I have read that the TPS should be adjusted to have one light on after warm-up with the ignition to the on position. But anyway I will check it with a meter. Do you (or anyone) know what triggers the secondary injectors to start? Is it a signal from the TPS to the ECU?

Thanks again. Any other posts are appreciated.

hugues

Likely problems:
TPS
secondary injectors
clogged exhaust

The secondary injectors come on under three conditions:

1) the TPS is fully engaged
2) engine is under load
3) rpms are above 3,500 rpm

To check if they work, it's very easy to check:

- Disconnect the hose to the boot sensor (near the passenger side shock tower) [cap the end to avoid vacuum leak though] (this will make the ECU think you're under load)

- Disconnect the TPS (this will make the ECU think you are at WOT)

- Rev to above 3,500

You should hear the secondary injectors click (use a screwdriver to listen)

If they do click, that's good. It means the seconday injectors are operating correctly. Do the same experiment but this time don't disconnect the TPS. Do they still click. If not, then your TPS is shot. If yes, then your TPS is probably fine.

Have you tried just disconnecting the TPS and see if engine runs better (remember a disconnected TPS means WOT for the ECU, so possibility of plug fouling + cat fubaring + very bad MPG)

You could also have a clogged exhaust. Very easy to check. Rev to 4,000 rpms. Let go of the throttle. The vacuum should go down pretty fast. If slow to go down, clogged exhaust. You could also remove your O2 sensor and see if it runs better (this will open up your exhaust a bit if that's the problem but watch out for flames though)

Hugues -