[jmcdoodle]

I have owned my 86 Daytona for 17 years, I love my car. I have done just about everything imaginable to keep this thing running over the years but I have finely hit a road block. Over the last 6 months I have been trying to hunt down a problem that I had with the car starting and running fine while at idle but stalling once out on the street. After replacing several components (throttle position sensor, idle air control valve, and fuel pressure regulator) I finely got around to finding out the issue was the fuel pump. I replaced the fuel pump, cleaned the tank out, replaced the filter then cleaned out all the fuel lines with an air hose prior to reinstalling a new filter, pump sock, new fuel pump, and the gas tank. Car started and ran great. Here's the new issue:

While driving down the road car runs great, after a few minutes of driving the car will start bucking and stall right after I push the gas pedal down to accelerate. It doesn't happen every time, just when I push the pedal down as if to accelerate quicker.

Initially, I thought it was an ignition issue, so I started replacing even more parts (ignition coil, wires, rotor button, hall effect sensor, distributer cap) with no luck getting rid of the issue. I took the car to a "mechanic" to see if he could pin point the issue. He said it was for sure an Ignition issue and had me replace the ignition control computer. No luck, same issue. It did, however, make the car run almost like new as long as it is at idle.

I have also taken apart and rebuilt the entire throttle body to make sure there wasn't a clogged fuel line, or vacuum line somewhere. This also improved the idle dramatically.

I am now at the road block listed above and cannot figure out what is causing this thing to stall under load. I am thinking it may be the Cadillac converter? Anyone had experience with this symptom and a bad Cadillac converter? Any other suggestions would also be appreciated. I am really stumped on this one and need some outside ideas.

Thanks everyone for your help!

Jeff

 

[Bob Lincoln]

It's called a 'catalytic' converter.

Do this first - check fault codes and report back what you get: http://www.allpar.com/fix/codes/index.html

It could be many things, but it sounds like the mechanic did not do a proper diagnosis. One possibility is the oxygen sensor. It is not used for the first two minutes after a cold start, but then can cause bucking and poor gas mileage (at least 1/3 lower than normal).

 

[jmcdoodle]

Yes catalyic converter, spell check got me.

I have checked the error codes periodically while I have been working on the car the past few months. I have not, however, checked them since rebuilding the throttle body. Codes before the throttle body rebuild were (25,33,52).

Ok, here are codes that I am getting currently:

12
25 - AIS Motor - I replaced this about 3 weeks ago. The error went away, the problem I'm currently having still existed. It has come back since then, I will need to check my wiring and vacume lines again. Maybe left something loose after rebuilding the throttle body.
33 - A/C Cutout Relay - Car was factory without A/C
55

I replaced the O2 sensor back in 2001 along with the EGR valve. I was getting codes back then indicating that they potentially needed changed, along with the engine running very rough. Changed them both and car ran well again.

Thanks.

 

[Bob Lincoln]

I'll bet that the wiring harness behind the valve cover has cracked insulation and wires are shorting. Check the whole length carefully. This is common.

 

[Bob ONeill]

Been there, done that. I've had my '86 for 27 years and have gone through the wiring and connector issues for some time now. Bob Lincoln and I traced my entire harness only to find a connection at the computer in the kick panel. I pulled the connectors and several of the spring connectors had lost part of their 'pieces'. I mean that part of the spring connector had fallen off. This made it nearly impossible for the connector to make solid connection to the pins. I replaced them and the problem finally went away.

I'm not saying that is your problem but between Bob Lincoln, you and me I'm sure we can solve these problems.

Check out the link in my signature for a page about error codes and drivability issues. Bob Lincoln and I co-authored this and hope it will help you solve your problems.

The harness in question here is the one which goes behind the valve cover. It's baked by the heat of the exhaust. In my case the insulation had flaked off the wires so they were either touching or grounding. I had to replace the harness or rewire it to solve the problem. Also the connectors at the ends of the harness throughout the engine compartment tend to tarnish and make bad connections. Consider disconnecting every one, one at a time, and clean the connectors. Tighten where possible each female connector and use some dielectric grease when reconnecting.

Please keep us informed as to your progress. One of my '86s (the one I've had for 27 years) has over 321,000 miles and on my trip from Tampa this past weekend performed very well providing 31.5 MPG.

 

[jmcdoodle]

That is very interesting that you mention that wiring harness.

For a long time I had noticed that the wires behind the valve cover were very hard and brittle coming out of a harness. I didn't mess with them in fear of causing a short or breaking one of the wires. While I had the throttle body off the car I went ahead and replaced the wires that ran from the harness to each component (AIS, Temp Sensor, O2 sensor, and Throttle position sensor) I did not replace the harness itself or the connectors at the components. I had went to the junk yard to try and find a engine similar to mine that had a harness with wires that were in better condition. I had no luck. I did find a harness that was similar on a newer model engine but it had 2 extra wires coming from the harness then my car has. Instead of putting the harness I found at the junk yard on the car, I just replaced the portion of each wire coming out of the harness that was brittle. Cutting about 1/2 inch from the harness and soldering a new wire on to the old. I wish I had replaced the entire harness; I should have posted here long ago. The connectivity in that harness may be the cause of the AIS code reappearing, just a guess. I will for sure take your advice and clean all of the connectors and apply dielectric grease. I will also check the wires running to my logic module. I replaced the MAP sensor before I changed the Fuel pump, I may have an issue with the connector there.

Do either of you know where I can buy a replacement harness? I would like to put new wires as opposed to getting them from a junk yard.

Thanks for your help. I will keep you informed on the outcome of checking the connectors.

 

[Bob Lincoln]

Sorry, I replaced my harness with a spare from my old car before I junked it, the old harness is long gone.

 

[Bob ONeill]

The first time I did this I rewired/replaced the bad wires. But then I located another harness and replaced it. But it's been so long that I may need to revisit this again.

There are not that many wires in this harness. If you can locate some wire that has insulation which could be resistant to heat then I'd rewire it. But, that's just me.

 

[Bob Lincoln]

Teflon wire is good to 200C and is best for this. But even polyethylene insulation is good enough, if you use the corrugated plastic shield over it. Don't use PVC insulated-wire, it's only good to 60C (140F) and will soften and melt together.