Fuel problem

[Saint]

Hey Hello my name is James,

I need a little help. I have a 1.7l DJET
that has a stu tt tt tter! I just replaced the throttle valve sw., it has a new Ignitor
pointless ing., and all new injectors. All other maintenance things (valves,oil,ff,...) I've just done. I runs GREAT, until it get hot, like in traffic. It gets real lean, and basing it on my 20+ years VW/Porsche carb experience I'd say it has a blocked jet. Some times it pops in the middle of acceleration. Also pops on deceleration bad.
You know like POP! No there is NO exhaust leak, I know better. If it could just stay cool like in the morning I'd be all set.

Please any suggestions/help would really help.

TIA

James Saint

[mejulihn]

How about starting with the head temp sensor located near the #3 cylinder (also known as "temp sensor II"). As the engine heats up this sensor sends signals to the ECU to lean the mixture. When disconnected in an FI car, you cannot start the car. Check for a loose connection or cracked wire leading to this sensor that may be causing an intermittent signal.

[HMeeder]

Yeah, gut feeling is the CHT. Check the connections and then if they seem good, you may need to replace it. They run around $20 or so.

------------------
Herb
'72 1.7 Tangerine 'Teen
'74 2.0 Red Rustmobile

[Jim Smolka]

Since you live in CA, you could bring it by Pelican and have them test your ECU also.

However, I would check the CHT first.

[pbanders]

Hmm. Like others have suggested, the CHT might be the cause. Since the CHT is a NTC resistor, its resistance drops with increasing temperature. One thing you might want to look for is to see if the spade connector from the sensor or some other exposed part of the wire is touching ground. Grounding the CHT produces a very lean mixture. Use shrink-wrap to insulate all exposed areas.

When hot, the CHT should measure 50 to 100 ohms. If you're measuring significantly less than 50 ohms when hot, then the sensor is likely bad. Check my D-Jet parts page for the correct replacement part.

Brad Anders

http://members.rennlist.com/pbanders/djetparts.htm

[Saint]

Thanks so much for repling so quickly.
So I went and checked the CHT sensor.
With my Fluke 87 she reads 1.643k Ohms at
approx 75 degrees cold.
I turn it on and ran it for 30mins. One quick note; the values I got while the car was running were OL(to start) and then dropped from 28.00M ohms down to 9.0Mohms.
(This is with the pos lead attached to the connector at the top of the pigtail.)
Readings with the car at 15 and then 30 mins:
15mins = 100ohms
30mins = 60.5ohms(this is where it settled)
So what do you think? Should I pull it? How can I "sneaky pete" it out. Also, how about the lead attached to the CHT. Does it disconnect from the top of the sens, so I can get a socket on it?

adv-Thanks-ance,
(thanks IN advance)

James

[mejulihn]

Paul can comment on the resistance values you measured, but it sounds within normal limits. The lead wire to the CHT sensor is permanently attached to the unit and has to be coiled up inside a deep well socket during removal/installation. I suppose you could cut it off on the old one you remove, but you will still have to deal with it when you install the new one.

[pbanders]

The hot and cold values look ok. If the wire and the connector are properly insulated against shorting, I'd look elsewhere for the problem. Perhaps your Pertronix has a problem when hot - try switching back to points and see if the problem goes away.

Brad Anders

[Saint]

It did it again to day. Only when it gets hot. All of the wires are o.k. I have a bad habit of always stripping, soldering, and shrink wrapping all of my repairs.
I have another question: Could it be my fuel
pump being mounted still in the back? Could the fuel be vaporizing at hi temps? Has anyone heard of it doing this? I know they were saying it helps with Vapor lock, and performance? Could the performance portion do this?

James

[Saint]

I have another question!! Could these be a stuck open AAR? Could this being open cause the very lean condition when hot? Could the stuttering be caused by the air box not having all of the vacuum it should, so the dist is not reading the load correctly?

Thanks for any Replies.....

James

[pbanders]

Originally posted by Saint:
I have another question!! Could these be a stuck open AAR? Could this being open cause the very lean condition when hot? Could the stuttering be caused by the air box not having all of the vacuum it should, so the dist is not reading the load correctly?

Thanks for any Replies.....

James

I don't think so. If the AAR were stuck open, you'd simply have air bypassing the throttle, and your idle would be quite high. The engine doesn't care if the air comes from the AAR or the throttle, and the MPS would sense the correct level of intake manifold vacuum. I still think it would be worth a look at your ignition. Some of the electronic ignition systems have a tendancy to cut out or work poorly when hot. Switch in your points and see if the problem goes away.

Brad Anders

[Saint]

It very well could be a ignition problem. When I first put the
Ignitor in the car it hung the dist all up. I had to take the whole
dist a part and clearance everything. After that it all worked
great.

I didn't know that some of those ignition
sys. have heating issues. I never would have changed
over. Is it a isolated issue or is it a manufacturer issue?
How can they sell their product as a "direct" points replacement?

TIA

James

[Saint]

So I wanted to update everyone. Mr Brad Anders wins the prize.
Yes, returning to the ATFII condition solved the problem. I runs great now. It's still not as smooth my old 914 with the carbs. Will it ever?

And also a big thanks to ALL who aided me.

Now, Pelican Parts,
I want my money back on the Ignitor!!

James

[pbanders]

James, I'd suggest seeing if Pelican will do a warranty exchange on your Pertronix. I've got a Crane XR-3000 in my car and it has worked flawlessly through the Phoenix summer, so there are electronic ignitions that do work when hot. Some people have had good luck with putting the Crane control box in the rear trunk and running the cabling through a hole in the plastic bucket for the top latch. Glad you were able to identify the problem!

Brad Anders