Engine miss fire @3,500 rpm ???

[scooter55]

Majicwrench I did just what you said and tested the pressure while driving. The pressure never dropped. It was around 30+ lb the gage bounces around between 30 and 35 or so it pulses . If you are steady on the gas it stayed at 30 lbs
Timinator I did have a problem many years ago with tha ect it made the car run very rich intermently. Thanks for the tip I will change that out. How do you probe the ect ? I am guessing reading the voltage at different temps ?
Mark thanks for that tip I will wiggle all the connectors and try to get it to miss. I have not yet free revved the motor to see if it misses with no load . I will report back and let you know if it does. I promise to let you all know what was causing this mystery as soon as it is solved. Thanks for all your efforts. After rebuilding the whole motor I am so close to enjoying this great car again . Just this one last challenge .

[majicwrench]

"Just this one last challenge" yeah right. heheheheh it never ends......

[scooter55]

So true.... But ever the Optimus ..
The car has been extremely reliable for the last 24 years. And on the bright side you can actually fix These cars. I feel sory for people with modern performance cars when it comes time for a restoration. I think the cost of all the electronics would make it impossible to restore.

[scooter55]

OK I just changed out the ect and it had no effect I had high hopes for that. I did check to see if it misses when not under a load. It does not. It will however miss at 3500 in any gear once warm. When I say miss it may be misleading. It is a sudden change in the way the revs are building. Much like a rev limiter. I do not know if it is one or more cyl being effected. Seeing how it does this only under a load makes jigging wires and such impossible . PLease HELP I am at the end of my rope

[azruss]

may want to don your earplugs and disconnect the exhaust at the manifold and see if that changes anything. if your issue drastically changes then you have a restriction in the exhaust.

[scooter55]

I will give it a try

[timinator]

Testing fuel pumps requires two separate tests. One for pressure, one for volume. Try your volume test when it is missing and see how long it takes to fill a quart container. The pump manufacture will have data for volume per minute of unrestricted flow.

[majicwrench]

Dropping exhaust is tough to tell diff sometimes, they get SO LOUD!!!!! Better to run backpressure test.
Drill 1/8' hole in exhaust pipe in front of convertor. Get cheapy vacuuum/pressure and put on rubber nipple. Now have someone rev engine to about 3k and hold it there. Check pressue. SHould be 1lb or less. If pressure is more, you have problems. You don't need to worry about loading it. When done run sheet metal screw in hole.
Correct me if I am wrong, but in an early post you indicated sometimes it works fine. Is it constantly doing it under load?
Keith

[scooter55]

Well instead of dropping the cat ,I noticed that there was a pressure test bolt in front of the cat. I figured if I took the bolt out it would relieve any extra back pressure from a possible blocked cat. The hole is about a half inch across.I drove the car with the bolt out. Unfortunately the problem was not cured Do you think the opening is big enough to free up any potential back pressure? The car did seem to rev up nicer. But the miss reappeared as so as it warmed up in 15 min.

Keith , yes sometimes it runs fine even after it warms up. As a mater of fact sometime in between shifts it will not miss at 3500 and rev like normal. Then next gear shift it will miss at 3500 again. If I keep my foot down while it is missing it will very slowly gain rpms but it will seem to struggle to gain rpm. Then it might clear up and shift completely normal right through all the gears. When it is missing at 3500 if I keep my foot in it it will not clear up as long as I am accelerating in that gear. I will put a pressure gage in the port and see what it reads. You say it should not be over 1 lb when racing the motor to 3000 rpm?

Timinator I can't test the flow rate while it is missing because it only misses under load. I did install a new fuel pressure regulator today and it did not help. I already swaped out the fuel pump with another used one I had and it did not change the symptoms. It was however a used fuel pump so I do not know for sure it was up to par. I could order a new one but I hate to keep throughing money at it.
I put in a new magnetic pickup,when I rebuilt the motor, what are the chances it is faulty? It is one of the only pieces of the ignition that I haven't switched out with another. As you can tell I am getting desperit

[scooter55]

Another thing how is it possible that I have a 30+ year old exhaust system from the engine and including the cat. It has not rusted threw. As a matter of fact it looks great.What kind of metal did they use Mean while the metal they used for the car will rust if you look at it. Just saying....... Now back to my problem.....Help

[majicwrench]

Go ahead and test the pressure at that port. A lb or so is fine, if it is pluggin it will get to two lbs or so, let us know. But if it works good sometimes, heck you may not catch it even if something pluggin exhaust.
BUT if you want to get creative, rig a pipe fitting of some sort in there, and again, run a hose up to windshield, and put gauge up there. Now go for a drive, watch gauge when acting up. Whatever sort of hose you use is not gonna last very long, but should work for while.

Worked at a Honda dealer in the early 80's. A fellow tech was fighting one, intermittently would fall on its face. I happened to be walking behind the car, could hear it "put-put-put" out tailpipe, then "pu---ffffff" a baffle in muffler would flop up against the outlet.
Good luck, I am going to be out of town a few days, hope to hear some good news when I get back on my computer..
Keith

ps Fuel pressure and volume.............if you have good pressue under load that means pump is trying to deliver more fuel than the engine is using. You do not need to know volume.

[scooter55]

I dropped the cat and ran the car with an open pipe. To my surprise the car ran worse. It had no power at all and would stumble at idle . But I did not have a miss in the short time I drove it. I put in a different cat ( one that i had for 15 years sitting in my shop) and took it out for a ride. It did miss a couple of times but then seemed to clear up. I took it on the highway an did 70 mph for about ten min. When I stopped for a light the car would not idle. Just got the car home and looked at the cat. It was glowing orange! So I am thinking that it was miss firing or running rich and dumping fuel into the cat. I plan on making a test pipe out of one of the cats and see if the cars idle returns to normal. one thing I am thinking is I guess I can rule out bad fuel delivery ,seeing how the cat was glowing? Does this latest info shed any light on the problem ?

[timinator]

ps Fuel pressure and volume.............if you have good pressue under load that means pump is trying to deliver more fuel than the engine is using. You do not need to know volume.

Although this seems to make sense, it is just not true. It is not common, but once you have seen it happen there is no more discussion. Having changed pumps it seems unlikely. Might be interesting to you to see what happens anyway.


Glowing orange cat would indicate fuel burning in the exhaust. Was the strata in the old cat melted? Running without the exhaust would lean out the mixture. Could have been your problem all along. How well does your o2 perform. Do you have access to a wide band?

[chrisfiat]

have you looked at the plugs ? if not then do so and let us know what they look like, if so then how are they?

[scooter55]

Chrisfiat, glad you asked I just pulled them. 1,2,4, look the same a little fluffy black Down around the mettle part of the plug the ceramic holding the electroid is white . The plugs have only 100 miles on them,so I
Wouldn't expect to see a nice brown plug. But #3 plug is a different story it is shiny black all over. Not oily and wet,but a thin shiny black that looks like it could be fuel from an intermittent miss in that cyl. Which would explain the fuel burning in the cat. And the miss at 3,500. I am thinking that the injector is hanging open some how or not spraying a mist. Making the cyl miss. The compression is good across all the cyl. New wires, new rotor , magnetic pickup, new plugs, new cap . So I find it hard to believe it is ignition. What do you think?
Buy the way I made a test pipe and got rid of the cat.the matrix on both cats looked fine. I do not think they were a problem at all. But it should run better without once I get this problem solved.
Timinator I do not have access to a wide ban but the o2 is new. Why does it run lean with a straight pipe ? I never would have though that.

Edited for spelling