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So I've moved onto the throttle body. I've read a bunch of threads where people complain about their car running like **** after removing a whole bunch of idleing mechanisms (who would've thought hey?) so ideally I'd retain the non-emissions related functions. Upon inspection it looks like part of my thermowax system is damaged. Specifically some of the plastic nipples where vacuum hoses would slip over.
Is there any recommended way to fix this? Hoping the answer isn't to buy new ones
As mentioned previously that system is completely useless. In fact I'd imagine it is already broken: check if the double throttle diaphragm (the thing that line with the check valve goes to) holds vacuum. Most of them seem to have disintegrated by now. If it did thats is a very small vacuum leak when the car is cold, that I doubt affects much if at all. Just cap off the line going to the thermowax. The purpose of the system is to protect the engine from too much abuse by limiting the amount of throttle you can give it when cold.
If youre really concerned about it, Im converting my car to carbureted, and im sure mine are still good since it ran like a champ. I will send them to you for cost of shipping alone.
If youre really concerned about it, Im converting my car to carbureted, and im sure mine are still good since it ran like a champ. I will send them to you for cost of shipping alone.
Wow super generous of you I appreciate that. I guess I didn't fully understand what the thermowax system does. I certainly never intend on driving a cold car hard so I suppose I don't need it after all but thank you for the offer
Wow super generous of you I appreciate that. I guess I didn't fully understand what the thermowax system does. I certainly never intend on driving a cold car hard so I suppose I don't need it after all but thank you for the offer
Just to clear up any possible confusion, the thermovax itself is something you want (so you don't have to keep the pedal pushed when cold), but those vacuum lines are not needed. The thermovax also happens to open/close that line, thats about it.
OP, I would provide the opposite advice from above.
The throttle limiting system is there for a reason. It is true that it keeps some cold air from going in your engine and grenading it, but it is a mechanical safety to ensure that the ECU can accurately measure intake air temp at the throttle body. That thermowax putting vacuum to hold the secondary throttle valves shut doesn't take much additional engine heat to open up. However, if it is cold out, <~75 F, the intake air thermosensor isn't in the usable range for the ECU. That thermosensor is meant to operate at a higher temperature range, as noted by the inspection temps in the FSM. The coolant loop that runs up through the throttle body is used for the Accelerated Warmup System (the other thermowax), but that function could just as easily be allocated to a solenoid. The coolant is fed to the throttle body primarily to heat up and stabilize the Intake Air Temp sensor so that it can accurately measure the hotter, post-turbo air. The intake air sensor in the MAF sensor receives a much cooler air charge, ranging from freezing temps, up to ambient temperature. By preventing the secondary valves from opening, you limit the capabilities of the engine to produce boost initially, until the engine sensor temperatures are in a state for the ECU to accurately account for intake air pressure and temperature states. That system is more important if you live in a place that gets below 50F. If you live near the equator, it is less needed, but if you live anywhere it is cold, it is an important mechanical safety to make sure your ECU is properly controlling your fuel delivery.
I would advise making sure the system is working properly, check valve, thermowax valve, vacuum lines, and coolant lines. Ruining an engine can happen in a few milliseconds. If you would like advice on how it hooks up correctly, we can take some pictures and help understand diagrams. Did I miss anything greybeards?
Edit: Most definitely keep the coolant lines to the throttle body. They are there to help the ECU!
Last edited by professionalpyroman; 02-02-21 at 07:28 PM.
Just to clear up any possible confusion, the thermovax itself is something you want (so you don't have to keep the pedal pushed when cold), but those vacuum lines are not needed. The thermovax also happens to open/close that line, thats about it.
Hmm so the thermowax will still do the throttle adjustments even without any vacuum lines hooked up? What is the purpose/function of the vacuum lines and check valve if they are not needed?
professionalpyroman makes a good argument to retain the system. My engine is N/A so some of the turbo stuff he mentioned doesn't apply to me but having 90% of the system in front of me is somewhat motivational to just get it fixed up. Is it really not possible to glue, melt, epoxy, etc, a plastic vacuum nipple onto where the previous one had snapped off like in the pictures?
Yes the thermovax will work without the vacuum line, the line only actuates the double throttle. Did you check the double throttle diaphragm? If its broken you'll need to replace that too. All in all I don't see a point in removing this system, but I also don't see the point of performing costly repairs on it if it broke. With a car like this I'm already conscious about not trashing it when under operating temperature, but hey if you want the extra insurance go for it.
Now if the diaphragm is not broken or you are willing to spend the money, I'm pretty sure you can JB weld the nozzles back then sand it down to look presentable. Melting it together might work too, but I would not try that on the thermowax. These are not really under a lot of stress so it should be fine, just be careful when installing the lines.
You have two separate thermowax systems working at your throttle body. One of them is not pictured here, and is responsible for holding your primary throttle plate open until the engine is warm. This Accelerated Warmup System (AWS) is meant to raise engine idle when cold so that engine heat can bring the intake air thermo-sensor (previously discussed) up to operating temperature. It is directly bolted to the side of the throttle body and has a linkage that rotates the primary throttle shaft. It uses no vacuum lines
This system that we are examining here is the other thermowax system that is responsible for keeping the secondary throttle plates closed until the engine can warm up the throttle body. It uses manifold vacuum (produced when throttle plates are significantly closed) to actuate a vacuum diaphragm connected to one set of secondary throttle plates and keep them closed when the engine is cold (see cold air flow). In this state, the thermowax valve connects the two vacuum nipples, and closes off the outside air port. The air then flows out of the vacuum lines, placing the vacuum lines, the interior of the thermowax valve, and the vacuum diaphragm under vacuum. The check valve, placed between the thermowax valve and the intake manifold, directs airflow exclusively to the manifold so that if the throttle plates open while the engine is cold, a normal driving condition, and manifold vacuum is lost, that vacuum is maintained in the vacuum diaphragm. This keeps the secondary throttle closed under all cold engine throttle conditions. Once the engine warms up, the thermowax valve moves, separates the two vacuum nipples, and opens the vacuum diaphragm side of this system to atmospheric pressure. This negates the vacuum pressure that was holding the diaphragm shut, and allows full function of the additional secondary throttle plates. The check valve and associated manifold vacuum lines are still under vacuum, but are deadheaded and non functioning. Once the engine cools down, this system resets to the previous cold state.
As far as repairing it, I have the same opinion of "Why not fix it?" However, from a practical standpoint, you could JB Weld epoxy it back on, but that plastic will still be brittle and it will be a matter of time until it breaks again. If you can find one in better condition, you will be all the better. As far as the check valve, those are fairly cheap, 5 or 10 bucks or so. If you are enterprising, save this broken valve, and see if it is feasible to 3d print a new plastic casing (you'd need to save the metal parts). I have been thinking about getting a 3d printer to mess around with this summer, but I haven't had the work this past year for obvious reasons. It would be nice for the community to come up with a set of files on how to remake some of these obsolete parts, but I may be an overly wishful person. Long story short, JB Weld should get you by, I'd look to replace that assembly, check valves, and replacement vacuum lines are cheap.
Based on the image I think the valve you have broken is the delay valve not the check valve. Check valve is between thermowax and the manifold, while the delay valve is between the thermowax and the diaphragm.
When googling delay valve it looks like the valve I took a pic of but you guys probably know better than me. It looks like this thread is the same issue I'm having https://www.rx7club.com/2nd-generati...-valve-939142/
In that thread OP calls it check valve but RotaryRocket88 gives an explanation to why it's actually a delay valve.
But just to summarize, I can simply cap off the diaphragm that the valve connects to the thermowax and the thermowax doesn't require caps on its nipples since it works off vacuum instead of actually pulling in vacuum?
You need to cap it at the source of the vacuum, which would be at the intake manifold. As RotaryRocket88 explained you either want to cap at the thermowax or at the UIM, but your thermowax nipple is gone so that is not an option.
The thermowax does not by itself pull a vacuum: the vacuum is coming from the intake manifold, the thermowax just acts as a heat-regulated valve on the line. pyroman's images explain this nicely.
I'm 100% sure the delay valve looks like that, I'm not sure if the check valve also looks like that or not. If it came from between the diaphragm and the thermowax that is indeed the delay valve.
I'd agree that that looks like a delay valve, and not a check valve. Per the FSM F1-35, the manual transmission NA requires 1 check valve, and the automatic transmission NA requires a check valve and two delay valves. In both cases, the check valve goes on the manifold side of the thermowax valve, and the two delay valves for the automatic transmission go between the thermowax and double diaphragm. The thermowax valve in the first photo has (or is supposed to) have 2 nipples on it, making it a for a manual transmission car, while an automatic would have 3. DirtyVert, I think you have plenty of info from here for either route you choose to go. Best of luck, let us know what you need.
Per the FSM F1-35, the manual transmission NA requires 1 check valve, and the automatic transmission NA requires a check valve and two delay valves.
You are using the S5 FSM, while, according to his signature, OP has an S4. I was also mistaken (or rather, did not check properly) as there is no check valve at all. Short story: there is a single delay valve, between the thermowax and the diaphragm. I checked this on my car as well and it is as described.
Long story: '88 FSM 4A-58, image 106 (top) shows the M/T system, with the delay valve between the thermowax and the diaphragm. On the same page the check valve is labeled "A/T only", the next page (4A-59) provides the testing for the delay valves: This mentions one delay valve for M/T and two for A/T. Image 111 on this page shows the A/T system, with arrows pointing at the A/T delay valves and you can also see the A/T check valve.
Additionally on other pages, like 4A-55, you can see the M/T system, with the delay valve between the thermowax and the diaphragm.
Lots of detail and helpful information in this thread. Thanks to everyone who helped out I think I have a better understanding of where to go from here
01-26-21, 12:23 PM
