7MGE miss or hesitation - Toyota Nation Forum : Toyota Car and Truck Forums

wambus · 07-27-2009, 12:58 PM

I have an annoyance I wish to address. I have not gotten on the engine with my multimeter just yet - I hoped to get some prime suspects in mind to shorten the process.

I have an 86.5 N.A. car. After the car is warm there is this hesitation; as if I had let off on the gas, even though I had not. I will mention that at certain speeds and situations (coasting between accellerating and decellerating) the car can start bucking. The coolant temp sensor is bad so I have capped off both ends of the connetor hose temprarily (since it was idling at 2100 RPMs when warm). I do not think it is the TPS as it only happens when the car is warm....?...

Any thoughts on what might be more likely to be the cause?

wambus · 07-29-2009, 07:26 AM

This hesitation is sort of a mini 'bucking'. I have found that it mostly goes away after a time, but then the engine does not have the power it should. It also pings a little in this state. The tach moves with the change in rpm only, not wildly jumping around.

I looked at the manual last night, but I am just not sure where to start. Distributor?

***bgrieger*** · 07-29-2009, 08:04 AM

checked for leaks yet?

wambus · 07-30-2009, 07:07 AM

Leaks from vacum or the intake (or both)? I have not had time as of yet. I hope to get a few minutes this evening to start poking around. Is it work pulling codes if no light is lit?

SupraTuned · 07-30-2009, 12:53 PM

Well, I think you should just take a day, and go through all systems like I did to find my engine problems. You should go through the distributor, check the points, check the spark plug wires, because when cold they will not arc (as much), and also if one is cracked it could be grounding somewhere, check your vaccume lines on everything, even the vsv's, test sensors with multimeter, just type in cygnus mkiii tsrm on google and you will find an online tsrm for our cars. They have all of the procedures for testing your sensors in there. Check for gasket leaks. It will be time consuming, but you may find what you are looking for. Hope this helps!

wambus · 07-31-2009, 09:46 AM

I replaced the cap and rotor a few weeks ago. I did notice a little better performance and much better gas mileage. I was planning of changing the plugs and wires just because... I also will change that coolant temp sensor and reconnect the related piping.

I have the factory manual so I have access to the values for various things.

One thing I noticed today. I have been using mostly Kroger gas (premium). This morning I put $15.00 worth of Shell gas (premium) in it. The bucking started as usual, but it quickly and almost completly died out. Hmmmmmmm. I have a can of WD-40 with me; this afternoon on the way home I will pull over when the bucking starts and spray areas that might have leaks and see what happens....

Jeeves · 08-03-2009, 05:04 PM

Gas does make a difference. I will also say that the coolant temp sensor is a relatively important engine calculation sensor. I wouldn't leave it broken long. That tells the engine when it's up to temp and adjusts fuel ratios accordingly.

wambus · 08-04-2009, 11:23 PM

So it is connected to more than just the 'choke'? I was thinking I need to go ahead and replace it.

wambus · 08-04-2009, 11:36 PM

There are 2 items on the housing for the thermostat. Is one for the temp guage and the other for the engine controls?

SupraTuned · 08-05-2009, 10:51 AM

The coolant sensor is the small spade one that threads into the side of the housing. Yes, a non working coolant sensor could mean all kinds of things happening, such as the car not running correctly in closed and open loop, the automatic advance not working properly, engine not burning fuel effectively....in truth, all kinds of things can occur when operating temperature is not reached relatively quickly and effectively. The problem is your computer does not know that it is getting up to temperature.

Jeeves · 08-06-2009, 08:48 PM

Thank you SupraTuned. It's been a very busy week at work and I hadn't made it back here yet.

SupraTuned · 08-07-2009, 11:14 AM

Thanks Jeeves. Figured I could shoot a little info in there quick to see if it would help!

wambus · 08-16-2009, 11:40 PM

I have replaced several vacum lines that were loose or appeared to have cracks or that were brittle.

I checked the coolant temp sensor - the one I checked has two prongs and is mounted higher on the housing than the one with the single spade (I thought that one was for the guage..?...

The resistance always seems very low, whether the engine is hot or cold. The manual says it should be something like 0.8 K ohms at 'normal' temp (I'm paraphrasing as I do not have the book in front of me...). I do not have a digital multi meter. When on the 1K setting, the needle drops well below 0. I want to be sure that it is really bad before I replace it...

I tried disconnecting the vacum from the EGR valve. Doing this made the bucking less harsh.

Also, the cold start injector time switch also appears to be bad. At 'cold' it reads 60 ohms. This is the low end of the range for the fully warmed up engine. When fully warmed up the meter reads 50 ohms - this is the upper end of the range for a cold engine.

I am focusing on coolant temp stuff because the problem exists only after the engine reaches normal operating temp.

What does the VSV do? How often do they fail

***bgrieger*** · 08-17-2009, 08:26 AM

The thermostat mounted BVSV opens the vent line from the fuel tank into the vacuum system so the engine can burn off any residual/extra fuel vapours rather than keeping them in the charcoal.

SupraTuned · 08-17-2009, 01:48 PM

I forgot to mention to you that your egr may be malfunctioning, which could cause these problems. Otherwise, in rare instances, the master cylinder could cause these problems as well. I see you have checked the egr already. Perhaps the master cylinder is acting up as well.