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View Full Version : occasional hesitation when turbo is kicked in


Mikezippster20
09-04-2004, 09:37 PM
I am the original owner of an 87 GN with 36,000 miles. It is stock except for a KN air filter. I have just tuned it up ( plugs, wires, fuel filter, coil pack) and still have the following problem:
When on the highway or going up an incline and the turbo kicks in (@WOT- manually,or close to it-cruise control), I notice the turbo lights go on(yellow and red), the car will start to hesitate, the red turbo light will flicker and gray smoke will appear out the exhaust. If I let off the throttle and punch it again it's fine. :confused:
I am looking for a scan tool to monitor the problem when it occurs but not sure which on to get, and then understanding it ?? that's another story.
I would appreciate any help with getting my car back to normal.

Keller
09-05-2004, 02:19 AM
...turbo lights go on(yellow and red), the car will start to hesitate, the red turbo light will flicker and gray smoke will appear out the exhaust...

The yellow and red 'turbo lights' tell me this is a digital dash car. Have a boost gauge? Any idea what boost level (i.e. a pressure) you are running? Any fuel pressure numbers?

My guess from your description, is that the car is running lean under boost, and starting to knock. Under severe knock the computer will start cutting boost back. You also could have a leak in the air tract between the MAF-turbo-IC-throttle body that would cause the MAF to have erroneous readings. Or just have a bad MAF.

Original fuel pump? If so, it may just be not up to par anymore. They were marginal to begin with, and the factory strainer in the fuel tank has been redesigned.

A scan tool could tell you a LOT more about what is really going on.

Mikezippster20
09-05-2004, 07:25 PM
Scott,
I do have a digital dash. I don't have #'s on boost or fuel pressure(no gauge's). It is original fuel pump and strainer. With the K&N filter I have an aluminum air inlet tube from the MAF to inlet and pretty sure no leaks. I will replace MAF and try that. About adjustable fuel pumps. Do I need one If I plan on keeping the car stock? I have been told the Autoxray 2000 scanner has a 29 second recorder to monitor sensors during track runs or problems like this. Anyone ever work with one??? Thanks again for the info.

Danin
09-06-2004, 02:58 AM
Correct me if I'm wrong, but wouldn't black smoke be rich, rather than lean? In either case, the fuel pump could very well be the culprit, I agree, though I also must note that you may simply have a low voltage issue with the pump. I found, when I picked up my '87, that the voltage getting to the fuel pump was closer to 6v than 12v, so I re-wired it. I ran an 8-guage from the alternator to a new relay on the sidewall, then back through the frame rails to the fuel pump, cut the postive on the disconnect and hooked my wire there. Then for a trigger, I used the screw to mount the relay as a ground, and the green (?) plug on the wire harness to turn it on, via a male spade connector. The green trigger point is actually used by -most- to activate their stock pump, but I find it works perfectly to activate your own relay. It cost me, in all, less than $30 to do this. I've also heard of people putting a relay in the trunk, with trigger wires and whatnot back there, but I found this easier.

Regarding the scantool question, I would heartily recommend DirectScan, which I've already said once today in a separate thread, but it still holds true.. http://www.bmcomputersource.com/Qstore/directscan.html
You'll need a laptop to operate it, but an old 386 will do the trick great, and it has an update rate FAR faster than the OBD/ALDL stream for these cars, as well as more sensor readouts, and a minimum of ~1min 30sec record time.

Mikezippster20
09-10-2004, 11:41 PM
Keller,
I just checked the fuel pressure, It is 34 psi w/key on, 29psi at idle, 34psi at idle w/ vacume hose off regulator, and was not able to get a reading at WOT( hose not long enough to see while driving). I am told by a mechanic that these are correct readings. is this true? I am also getting a new MAF and trying that before replacing fuel pump(full tank).
Danin,
I ordered that software (directscan) and hope to receive it soon. I am also following your problem, they may be related?

Thanks

Keller
09-11-2004, 02:58 AM
Correct me if I'm wrong, but wouldn't black smoke be rich, rather than lean? In either case, the fuel pump could very well be the culprit

Sometimes you may see a grey or white 'smoke' during a lean condition. Given that he has the original (17+ year old!!!!) fuel pump, that was barely adequate for a completely stock car when new, I'm guessing its had its due.

Only downsides to DirectScan is that it is not transportable from car to car, and works only with the 86/87 TRs and 89 TTAs. Also, it may frustrate some with the steep learning curve to understand, but those people will likely be befuddled by all scan tools. It is a great tool, and benefits from the fast data rate. Beginners, and non-racers may like other tools as well. (i.e. Turbolink, OTC4000, etc.) The Turbolink website has a great comparison chart at http://www.turbo-link.com/

Don't replace the MAF until you get some data from you scan tool and do a 'tap' test on it. (i.e. tap it while running and see if the car 'stumbles')

Keller
09-11-2004, 03:01 AM
I just checked the fuel pressure, It is 34 psi w/key on, 29psi at idle, 34psi at idle w/ vacume hose off regulator, and was not able to get a reading at WOT( hose not long enough to see while driving). I am told by a mechanic that these are correct readings. is this true?
Thanks

Since it should be ~33 PSI (*with all the stock pieces*), hose off, it sounds OK. At least at idle. No telling what it does at WOT. Voltage to the pump may be the issue. The factory wiring to it is very poor, with many breaks/connectors in the circuit. There are solutions to this.

Mikezippster20
09-11-2004, 08:50 PM
Keller,
Any advise on which fuel pump to replace my original one with? Again I don't plan on running this car so I don't think a adjustable pump would be an option. Have one in my WE4 and its a pain (was in the car when I bought it). I'm open to suggestions. I will rewire pump over winter with heaver gage wire. I like the turbo link, impressive, will see if I can work that. Thanks again.

Danin
09-11-2004, 11:24 PM
Congrats on DirectScan, I completely love the thing. Keller has a point, it is a tad steep, but it's really fairly easy to figure out working with it for a little bit. As for portable from car to car, I either swap out the ECM completely (keeping the proper chip in the right car) or modify both ECMs, it's just a simple nip tuck on the metal casing. The thing you REALLY REALLY need to pay attention to is the plug! That thing will VERY EASILY go on backwards! If you have ANY questions on it, let me know, I've worked with it on several cars.

Note 2, our problems may very well be related. Upon checking elsewhere, I've discovered my issue may be DIS-related. Under higher cylender pressures, the DIS system naturally has a harder time firing, due to higher density. Requires more power out of the coils to spark across the gap..I can't believe I didn't think about that. I'm working on replacing my own, I'll certainly let you know.

I'm still gonna try to pound home here, check the voltage at the pump! I can't stress this enough. Mine was 6v, one of the locals was down to 9v.. I agree with Keller, the stock pump might be toast, but MINE is okay, so keep that in mind.. Email me, let me know what happens.

Keller
09-12-2004, 12:09 AM
Any advise on which fuel pump to replace my original one with? Again I don't plan on running this car so I don't think a adjustable pump would be an option.

Uh...adjustable pump? :confused: Regulators come in adjustable flavors, but not pumps. Nothing wrong with an adjustable. At least consider a Bosch 237 (nonadjustable) regulator as a minor upgrade.

I would recommend one of the Walbro pumps. Think the model numbers are 307 and 340; the latter being a higher-capacity unit for similar cash. Racetronix, one of the site sponsors has an kit with all the installation bits for a nice price. check 'em out!

Casper's Electronics has a wiring kit that fixes the stock pump wiring shortcomings with a fused and relay-switched circuit. All Packard Electronics (i.e. Delphi/GM) connectors and completely plug-n-play. A nice piece. There may be others as well.

There are *7* connectors in the stock wiring between the battery and the pump. That's why it gets a very bad supply to the pump and degrades over time.

Keller
09-12-2004, 12:11 AM
Congrats on DirectScan, I completely love the thing. Keller has a point, it is a tad steep, but it's really fairly easy to figure out working with it for a little bit.

At this point, DirectScan and TurboLink are in the same ballpark pricewise.