Getting slow when hot

[FinGN]

Yep, first post from me here! Anyways, my 87 GN (102 K miles) is loosing a lot of power when getting warm. It drives quite good for about ten miles and then when warmed up, it looses power a LOT! It's stock, except for "hot wired" Walbro 340, adjustable FPR (set at 3 bar) and free flow mufflers. Cat is gutted. The tranny also starts to shift like an old STW tranny when warm. Any ideas what to do? We only have around 10 of these cars in Finland and the car shops don't seem to know anything about these cars here. Thanks in advance.

 

[NastyGn]

A first guess would be to go to the gnttype.org site and do the spring cleaning as a start to make sure you have a base line.

The second thing would be you may want to get a scan tool like Turbo Link or something like that to see what the ECM is seeing.

With a scan tool you can see if the car is seeing knock and the ECM is retarding the timing or is something worse going on.

Good Luck

 

[FinGN]

Thanks! I did the spring cleaning and that part should be covered. The car was also just at a local GM dealer who checked it, because it didn't pass our local smog inspection. They checked it with tech (dealer scan tool) and set everything by factory specs except the fuel pressure, (3 bar now). Now it passed the inspection after they replaced the o-rings from the injectors which were cracked. The car has been losing power after getting warm all the time I've owned it, only driven about 3K miles with it. Unfortunately we don't have scan tools available here so I can't access one so easily. I'll try to get one somehow, but in the meanwhile, if someone could present an educated guess what might be wrong, I'd appreciate it.

PS. A guy with a 86GN suggested it might be because of the thermostat and it should be replaced with a 160 degree one. Also he noticed that it has the infamous crack on the drivers side header. Could these both cause this?

 

[blackbuick87]

My guess would be to look at the coolant temperature sensor. If it does not tell the ECM your car is warmed up the computer will keep dumping fuel in the engine like it would on cold startup. You will be running REALLY rich

Since your tranny shifts funny you might want to take a look at your converter and make sure it isnt slipping

 

[FinGN]

Thanks for the advices. I'll try to check these things during weekend, though I doubt it's the coolant sensor, because the car did pass the emission tests now and the previously hi HC went down from 1570 to about 260.

 

[grey1]

COLD AIR WORKS BEST

 

[dconnor]

3 bar = ~43.5 psi if my brain is converting it right, if you still have a stock chip in the car it's probably running a bit rich. A 160° (fahrenheit) thermostat will help the car run cooler... cooler engine = more power. Do you have a coolant temperature guage on the car? If so what temp is it running at once warmed up & after cruising around town a bit? Is it throwing any SES codes?

Doug C.

 

[FinGN]

The car still has the stock chip, but I'm planning on ordering a Trasher 92 chip for it. Unfortunately the car doesn't have any extra gauges on it yet, so I don't know the temperature either, but I'm getting a 160 degree thermostat today. It doesn't show any SES codes, the light goes off as soon as the car starts. Do you think the cracked header might cause symptoms like this. Maybe the high temperature causes the crack to open up when hot and when it cools down it closes again? Just my guess.. Also about the tranny problem, I've been reading that not many tranny shops in US know so much about these transmissions, so I bet it's going to be a pain to find some GN tranny expert here!

 

[NastyGn]

To answer your question on the header yes this will cause you some greef. It will also give your O2 sensor some wrong readings the more it leaks.

Something else I wanted to ask. Have you checked all your vacuume lines? With age these have a history of cracking around there connection points or bends and with heat would leak more than when everything is cold.

Good Luck

 

[FinGN]

I went through all the vacuum lines when trying to find the cause for high HC. I replaced the S shaped one after the EGR and now they are all OK. If I remove the one from FPR at idle the vacuum is really strong even when hot so I don't think that's the problem. I'll replace the thermostat and test it after that to see if it has any effect. Regardinig the sluggish transmission there are overhaul kits and converters from both TCI and Transtar (overhaul only) available here through a local parts store. Any experiences if these are any good for GN transmissions?

 

[Red Regal T]

Your throttle position cable must be adjusted properly for good shifting. Also, try a shift kit first before going to overhaul.

Look into getting a scanmaster from one of the vendors here. That way you can have some idea of what's going on. They are about $250 and well worth the cost. Look into it.

 

[FinGN]

Thank's for the advice. It might very well be the TV cable. Seems that it doesn't make any difference what's the cables position, so it's probably worn out as one mechanic already suspected. I'll try to get the scantool asap. Seems that otherwise it's just guessing after guessing.

 

[John Larkin]

If you can solder, here is a free scantool provided you have a window-based laptop to run it on. It works almost like a ScanMaster. Good for starters until you raise funds.

WINALDL Scan Tool

 

[1badTTA]

Definately get the scantool, these cars are almost impossible to work on without one. And my bet is that the cracked header is causing most of your grief since it is happening once the computer goes into closed loop. Reset the computer (pull the orange wires by the battery) and see if is does it right away, if not it is probably your BLM's being way off from an exhaust leak.

 

[machinegun]

Where are you located in finland. I might be able to help you out with tools as our companies headquarters are in Turku. Let me know and I can probably help you out some.

 

[FinGN]

I'm located in Espoo, in the capital area of southern Finland about 100 miles from Turku. Scan tool is probably the first thing I would need, right next to a new TV cable. After adjusting the cable friday night all my tranny problems went away, but it seems that the cable doesn't keep its adjusments. After driving a while, some of the problems returned, like not upshifting in time. Also, the feeling of loosing power was partly because of the funny shifting tranny, sometimes shifting way too soon and sometimes letting the engine over rev. Thanks for the tip on the free scan tool, but I think I'll go straight to a real thing.

 

[NastyGn]

Something you mentioned that might be going on is that your solenoid for the converter lockup is going. If this goes the converter will stay locked up more and now want to unlock.

This will make the car feel like it's not down shifting.

Take Care

 

[FinGN]

Thanks, the converter is also a question mark. The previous owner told me that it has been replaced. Nobody seems to know what converter it is, so the only choise is probably to open up the cover and take a look. Thanks everybody for your input! This is a great source to get information on these rare cars!!