vegetarianpimp

Dear READER--- First of all, THANKYOU for welcoming me to this forum. My name is Donald, and this is my FIRST POST... I have a 1990 Honda PRELUDE "S" (1958cc/dual-carb/5-speed/189,000 miles/ALL STOCK/NO aftermarket modifications, whatsoever) with a STALLING/ROUGH RUNNING/LOSS OF POWER=ALL WHEN WARMING/FULLY WARM problem... The motor, itself, is mechanically sound (oil has been changed every 3000 miles, cylinders 1,2, and 3 each have 145 lbs of compression and cylinder 4 has 150 lbs. ALL cylinders hold compression well with no leak-down... Vacuum is 20 inches at idle and rock-steady... I loosened and re-tightened any grounds I could find... All 4 spark-plugs are clean with no fouling of any kind... Plug wires are good)... I live in Wisconsin and it is cold here at this time (20 degrees), yet the engine fires up instantly (within 1 or 2 seconds) and settles into an ultra smooth (I call it "Honda-smooth"--like a sewing machine motor) 1600 rpm "cold" idle... After about 3 or 4 minutes, the idle speed tapers down to about 1000 rpm (STILL ultra smooth)... THEN, at approximately the 5 minute mark (and WAY BEFORE reaching full operating temperature--the point where the cooling fans would come on), the engine speed suddenly drops down to about 200 RPM, the engine runs very rough, and it stalls (unless, I "catch" it with my right foot pressing down on the gas pedal)... I want to EMPHASIZE that this DROP IN RPM occurs SUDDENLY, as if some sensor or signal is activating or de-activating... This is a consistent scenario (same exact sequence of events, even during other attempts to start the car "cold")... Once the engine HAS warmed up to full operating temperature, it continues to run very ROUGH and has REDUCED POWER and gives off a strong GAS SMELL and will NOT hold an idle without help from my right foot on the gas pedal... By the way, the ECU "had" been giving off "code 6", which is for "COOLANT TEMPERATURE SENSOR", which I replaced and then reset the ECU by disconnecting the battery for 15 minutes... The new sensor made NO difference with regard to the stalling problem... There are currently NO check engine lights or codes (I checked again)... There is NO air in the coolant (I removed the bleed screw and the coolant was right up to the top of the hole)... The exhaust is NOT restricted in any way... The engine STARTS RIGHT UP "COLD" (runs VERY smooth) or "WARM" (runs VERY rough, but will only start "WARM" with "help" from my right foot on the gas pedal), SO, I am thinking that this is NOT an IGNITION problem, but more likely a FUEL or SENSOR problem... I previously owned an 89 ACCORD (carburated model), which ran GREAT (until an individual ran a stop sign and T-boned the vehicle right near the driver's-side/dashboard area and TOTALLED my car, BUT NOT ME, praise the LORD), and I still have the Honda Motor Company service manual for that car. I've been reading as much as I can about possible solutions, but don't have some of the test equipment that a Honda dealer would have... I also went to my local library and checked out a "Chilton" (not in the same league as the official Honda version) manual, which has been somewhat helpful... These motors are VERY complicated, with 50, or so, vacuum hoses--I don't want to just "GUESS" at what is wrong and throw "good money to bad"... I also have another car to drive, in the meantime, while I am trying to get my Prelude running properly again... PLEASE, HELP!... WELL, that's my POST... I look forward to receiving some insights into what is going on with this motor... THANKS, in advance, for your assistance, FORUM READER... signed, Donald

jlude90

First of all Donald, I want to thank you for the informative post. Its very rare that we get someone who gives that many details right off the bat, and that helps alot.

I have a 90 2.0S as well, and while I don't have that engine anymore, I know how much of a pain that is. And when I pulled it, I lost count at 64 vacuum lines...not fun.

As for the problem, it sounds like it could be the MAP sensor. I had a problem very similar to that on my new engine in the car. What I would do is dig into the vacuum box located on the firewall towards the passenger side, you'll see 6 or 8 vacuum lines running into it. Open it up and you'll see a sensor labeled MAP on it. Unplug that and see what the car does. It will trigger the check engine light, but thats OK. Let it warm up and see what it does. It should operate somewhat normal.

You can drive like this, but you'll be getting less power and poorer fuel economy as the ECU is putting in a fixed value instead of an input from the sensor.

Try that and see what happens. If not try www.prelude power.com and make a thread there, there are some knowledgable carb guys on that site.

vegetarianpimp

Dear jlude90--- Thanks, for your suggestion... I will plan on trying that... We had about 10 inches of snow, today, and my Prelude is out on the street... So, it will have to wait a bit... But, I will plan on getting back to you with the results... PEACE/OUT... Donald

Enzo15

This might be a stupid response, but why would a carb need a map sensor? The carb itself is supposed to meter the air and fuel. Im thinking the tuning on the carb would be off. With either too much gas being put in, or the carb not opening enough when at idle. Just a thought :D Definately check out wat Jlude was saying, I might be completely wrong XD

jlude90

If you've ever seen a B20A3 carb set then you'll know how over complicated Honda made carburation. There is still pressure regulation, all kinds of vacuum advance and retardations, and a whole butt ton of sensors. I'm actually using the MAP from my old carb motor on my H motor now, coincidentally.

But yeah, Honda wanted to make a carb setup as reliable and with as good fuel economy as an EFI motor, but I don't understand why they didn't just EFI-ize it.

Enzo15

Lol Ok. Ya I havent seen a Honda Carb, I just kinda thought it would be like a normal carb XD. Lol Ignore my advise lol, unless it has any potential XD

vegetarianpimp

Hey, jlude90--- Just wanted to let you know (months later!...) that I tried unplugging the MAP sensor but, unfortunately, it made no difference regarding the running problem... As it turned out, I listed the car on craigslist for $1050 and got about a dozen responses... the first guy to come over and look at it gave me my price... He was going to swap in a different motor, anyway... So, it ended well for both me and him... Thanks for your time... Don

92civlude

Im sure this car is running rich. Your best bet, Its in the carbs. Find someone who has experience in rebuilding these carbs. An older Honda Master Tech at a Honda dealership might be the right candidate. Replace the float sets, float valves, both economizer valves, and those two 10mm vacuum hoses on top of the carbs. If this doesnt fix it, exploratory examination while the carbs are apart will reveal the problem. Oh, I almost forgot, the vacuum advance diaphrams on the distributor always leak and retard the timing and cause a lean condition. This may cause a problem once the carbs are in order. Youre a smart one for selling it!

swin

having the same problem with my 88 2.0s ...started 2 days ago and i too adjusted the linkage...now it idles at @ 1500rpm..culd it be the egr valve?

Hotaru

Well I have the 2.0 S Engine and wanting to change it to the H22 later but I kinda need this car to run for me now, I have a similar but a bit different problem, I will get in my car and it drives fine and everything at first and will get up and go, I have out ran a 2009 subaru in it it has 103k original miles. here is my problem Drives great, and everything at first and everything the first time while it was still cold. but then I will stop and turn her off and go in even the convienent store, come out start her up---- sometimes she is hard to start sometimes she starts right away- this is I think that relay under the dash behind the Fuse box I will check that out but the other problem that concerns me is I will go driving down the road after I have gotten her started and she will shift into first and second fine and sometimes third but when it gets to fourth and after the initial shift and before the secondary it boggs down and just totally tries dying on me like it lost all its power and like I said it sometimes dose this in 3rd as well, there are other times where it won't do it at all.
things I have done so far are I have changed out both Fuel filters, I have checked the Fuel pump it is working strongI also have taken and Blown thru the fuel line at certain parts and cleared them out, so I know it is none of that. I have also gone thru the Spark plug wires and plugs as well as the Coil all of them are opperating fine I have not checked the Distributer its self but not sure that would be the problem, I was also kinda thinking it might be a sensor or something, I also have made sure it is getting Air into it and baught one of the STOCK style Air filters for $25 wix brand. if someone has some good sugestions on what I should look for or change out on this to get it to stop doing that I would really appriciate it, I also realize this is going on an old post so I was going to make a new one and copy it into it and change some stuff
Thanks

Hotaru

Thanks 1funryd I was actually looking at PP again and remembering my account for that site when I got an E-mail showing your post lol