Surging under load

[nitrofarm]

Hey guys my 93 has a strange surge under accel & wot. I know it must have the wrong thermostate in the engine. Cuz the engine never really gets hot.(havnt had time to pull housing yet) So I'm thinking this is allowing the car to stay in partial warm up mode? Engine idles great and it is not a engine miss. Its def fuel/eng magmnt. Does the VAF have any diagnostic test I can do? I know you can adjst TPS. But I dont see any test for the VAF? I'm hoping the correct eng thermostate will cure surge. Also anyone know when the ECM switches from closed loop to open loop ?Does it happen very quickly like back and forth when the engine is is fully warmed up? I noticed that the manual states that if the EGO fails it dont really effect driveabiltity. Your thoughts please. Thomas

[nitrofarm]

Update- Adanced the timing 2 deg which helped the surging. I really didnt notice it anymore. But the weather is warmer so that might be a factor. So I'm tossing the thermo thats in the eng now.And replacing it with a dual style. I have no idea what it is. But I'm betting its wrong !!!! I'll keep myself posted.....

[Pu241]

I know it must have the wrong thermostate in the engine. Cuz the engine never really gets hot.(havnt had time to pull housing yet) So I'm thinking this is allowing the car to stay in partial warm up mode?

So Mr.

How do you "know" you have the wrong thermostat and what do you mean by "the engine never really gets hot"?

[nitrofarm]

So Mr.

How do you "know" you have the wrong thermostat and what do you mean by "the engine never really gets hot"?

Uhhhhhh the Tempo gaugo never gets to half wayoo. And you can stick your tounge on the valve cover & not get burned.After reving it @ 6500 rpm for 10 minutes (sitting still). So I guess thats why I have a "HUNCH" that the thermostate is either stuck open.Or its the wrong part. You have any suggestions? Please let me know,thats why I'm posting here. We havent had this car long so what parts have been changed in the last 20 years is anybody's guess

[Flyin4stroke]

What have you done to the car? Have you given it a regular tune up... Plugs, wires, cap, rotor, oil change, seafoam if necessary. I would start here before changing a thermostat even if it doesn't heat up all the way that's good. Most people worry about over heating.

[nitrofarm]

What have you done to the car? Have you given it a regular tune up... Plugs, wires, cap, rotor, oil change, seafoam if necessary. I would start here before changing a thermostat even if it doesn't heat up all the way that's good. Most people worry about over heating.

I'm in Wisconsin Bro. We are forecasted for snow tonight. Car has 85,00orig miles Changed valve cover gasket last week. Valve train looked very very clean. Like I said its a fuel issue its not a miss. You can "Feel" the surge get faster slower. Not jerk jerk jerk like a spark miss. Cap Rotor wires plugs are good. And a cold engine is not a happy engine. Same as a hot engine is not good either. 210 deg thats what they should run close too. Weather its in Fl or WI

[Flyin4stroke]

Lol snow? What's that... Just want you to check your basics first. My car is turbo'd but I was having this issue right before my distributor went out last week. I guess the springs break inside the distributor and make it not advance like it should. I wouldn't rely on the gauges in the car. But that's up to you. My buddies car runs on hot all the time even after we have switched out the temp sensor. Runs like a beast though and doesn't get hot just FYI.

[Tom]

Put in a YELLOW bottle of HEET, not the red one. Moisture is like small B B's like you shoot in a gun. Actually smaller than that, more like the smallest of round steel bearings. About ten or twenty of to one BB. They can't pass through the jets when more gas is called for and bounce all around the fuel system causing countless havoc. The YELLOW bottle of HEET will go find and dissolve and neutralize these obstructions. Both summer and winter.

[Pu241]

Put in a YELLOW bottle of HEET, not the red one. Moisture is like small B B's like you shoot in a gun. Actually smaller than that, more like the smallest of round steel bearings. About ten or twenty of to one BB. They can't pass through the jets when more gas is called for and bounce all around the fuel system causing countless havoc. The YELLOW bottle of HEET will go find and dissolve and neutralize these obstructions. Both summer and winter.

Wow Tom, I'm not sure where to start!

Do you know actually know the difference between the "YELLOW bottle of HEET" and the "red one"?

In fact the yellow one contains isopropanol which also happens to be one of the prime components in Seafoam, a well regarded fuel system cleaner.

Moisture comes dispersed in gasoline in sub-micron particles all the way up to puddles in the tank, depending upon ethanol and dispersant's content of the gasoline. Primarily due to being mixed by the pump at the station. The longer it sits undisturbed in your tank the more of it will coalesce into larger drops and even a puddle on the bottom of your tank.

The OP has a '93 festiva meaning it is EFI, NO JETS!
So water just "bounces all around the fuel system causing countless havoc"?
I can only hope you don't work on other peoples cars.

The yellow or red bottle of HEET (methanol base and isopropanol base) DO NOT dissolve water. Both methanol and isopropanol form an azeotrope with water and gasoline so that the water can be safely injected into the combustion chamber and eliminated. It just so happens the isopropanol product (red HEET bottle) can handle more water than the methanol based (yellow HEET bottle).

[Pu241]

Uhhhhhh the Tempo gaugo never gets to half wayoo. And you can stick your tounge on the valve cover & not get burned.After reving it @ 6500 rpm for 10 minutes (sitting still). So I guess thats why I have a "HUNCH" that the thermostate is either stuck open.Or its the wrong part. You have any suggestions? Please let me know,thats why I'm posting here. We havent had this car long so what parts have been changed in the last 20 years is anybody's guess

Temp gage is a bad indicator of engine temp.
The gage is independent of the sensor that provides the ECU temperature data.
Unless the connections to the gage sender are very good and clean your gage will always read low.
The top of the valve cover is not a good indicator of engine temp.
check the upper radiator hose which moves water from the head to the upper radiator. If it remains cool or only warm after a 5-6 mile drive at 45-55MPH then you do have a temperature issue and could in fact be a stuck thermostat or possibly the thermostat was removed completely.

[Tom]

Wow Tom, I'm not sure where to start!

Do you know actually know the difference between the "YELLOW bottle of HEET" and the "red one"?

In fact the yellow one contains isopropanol which also happens to be one of the prime components in Seafoam, a well regarded fuel system cleaner.

Moisture comes dispersed in gasoline in sub-micron particles all the way up to puddles in the tank, depending upon ethanol and dispersant's content of the gasoline. Primarily due to being mixed by the pump at the station. The longer it sits undisturbed in your tank the more of it will coalesce into larger drops and even a puddle on the bottom of your tank.

The OP has a '93 festiva meaning it is EFI, NO JETS!
So water just "bounces all around the fuel system causing countless havoc"?
I can only hope you don't work on other peoples cars.

The yellow or red bottle of HEET (methanol base and isopropanol base) DO NOT dissolve water. Both methanol and isopropanol form an azeotrope with water and gasoline so that the water can be safely injected into the combustion chamber and eliminated. It just so happens the isopropanol product (red HEET bottle) can handle more water than the methanol based (yellow HEET bottle).

That yellow $.99 bottle of Heet, like sea foam, cures a lot of problems. -- A lot of problems. It's the first place to start. EFI or Carburetor.

[nitrofarm]

Temp gage is a bad indicator of engine temp.
The gage is independent of the sensor that provides the ECU temperature data.
Unless the connections to the gage sender are very good and clean your gage will always read low.
The top of the valve cover is not a good indicator of engine temp.
check the upper radiator hose which moves water from the head to the upper radiator. If it remains cool or only warm after a 5-6 mile drive at 45-55MPH then you do have a temperature issue and could in fact be a stuck thermostat or possibly the thermostat was removed completely.

Hey Pu241 good education on the "HEET" I never took the time to even look at the difference on the bottle.I always just used the yellow,but now I know. And I had no idea about the chemical composition being similar/same to Sea Foam. I will get my Raytek and get a temp reading @ the outlet of the radiator after taking it on a good beat run. And based on that we can make some decision's. I really Appreciate your guys help.
I still would like to learn this efi system better. I grew up on carbs. Got educated on Fan Jets,turbo props & Carb'd plane engines. They never use efi. But know its time to learn.It actually is a little less tough than I thought.Once I started reading I was like. Ohhhh so thats how these kids can keep their little rice burners running! Its basically all done for you! No messing with accelerator pumps,needle & seats, jets,points etc..
So my ECA only appears to have 3 main outputs. Injectors, Idle speed control bypass air, & canister purge. The "BOOK" says that "timing" is entirely controlled by the ECA. (So I dont know why they dont consider that four outputs?) But anyway if one of you Gents would like to help get mea little up to speed on efi that would be cool. I understand that the Base Engine Strategy has 8 different "MODES". And I understand 6 of them. But there are two modes where I'm a little shakey. "Closed Loop" & "Basic-Control Open Loop". It appears that when its in Basic Control Open Loop "Mode" that all is normal. But it seems likethe book is saying that the o2 sensor isnt in this mode at all? Is this right? It sounds like they are saying that the o2 sensor only gives the ECA input in Closed Loop "Mode".Is the ECA switching back & forth between these two modes during normal conditions after warm-up mode is complete? I know a lot of people think "Who cares's, if its working dont worry about it"! But by knowing how my system works. Is the best way I know how to fix it when its not working. Thanks again...
Your thoughts.... Thomas-
PS I'm really just like an old Ricky Bobby. I just wanna fast !

[blkfordsedan]

After reving it @ 6500 rpm for 10 minutes (sitting still).

:shock: You serious Clark?

[nitrofarm]

:shock: You serious Clark?

Hah ! No but I really did stick my tongue on the valve cover :confused2::confused2:

[Mike McKown]

Hey guys my 93 has a strange surge under accel & wot.

I went throught he same thing with thermostat, timing, etc.On this paticluar car, it's not like yours though. Mine had many, many miles on it. Lot's of blowby. The air intake had a lot of oil in it, even running down into the air cleaner element.

Aside from the blowby, I found the baffles in the valve cover for the fresh air intake were plugged with sludge. So, I cleaned them out and the surge went away.

Before I did this, the car would experience intermittent periods of blowing blue smoke under load, spark knock and surging, as in your case. Now, all it does is just use oil. The exhaust smoke is gone, spark knock is gone and the surging is gone. Bottom line is the engine is worn out and needs a rebuild.