16949

[16949]

Emptied the fuel tank upon purchase. Breathed on the fuel pump, had to replace that and now the boot needs replacing. I plan to just swap for the all in one, I didn't want to replace with the old style in the first place and now I have a bunch of variables that have been changed.

Meanwhile, I have to figure out what is causing it to run differently after 45 minutes. I am taking over repairs, where possible and I can plug stuff in so this is as good a place to start as any.

I took some pics of my fuse box. Ordering bitsyncs rpm relay. Probably need other things too?

Anyway, here's the Delorean porn:

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[Ryan S.]

Replace relays and fuses, if you haven't done so already.

[DMC-81]

Hi there,

Dave McKeens RPM relay is a good upgrade, as is DMC's fuel pump module, although it's not a simple part change, as they recommend cleaning out the fuel tank before the installation. Looking at your relay compartment, ( nice porn by the way ) I can't tell how old your relays are, but they appear to have been changed at some point. I would suggest determining if you have any electrical issues (like the climate control fan speeds) before I would change them at this point. 45 minutes is a long time before the engine changes it's "tune", so perhaps it's an electrical issue, but it could be a number of other things. Regardless, when it comes time, I recommend the relay upgrade.

Can you describe how it runs differently ? Perhaps a video of the engine running, even pictures would help, especially wires/connections and vacuum hoses. That will help us diagnose what is wrong.

Do you have any history on the maintenance? It would be good to know if any tune up parts were done, and how recently.


Cheers,

[Nicholas R]

In my experience, when the engine changed it's tune after running for a while it was one of 2 things. Either the ignition system (in my case it was the ignition coil), or what seems more likely is probably the lambda system (only applicable if you're running closed loop, which you likely are). When you first start up, everything is cold so you dont really get any response from the lambda system. After it runs for a bit, the O2 sensor heats up, warm up regulator comes up to temp, etc. lambda takes over fuel management. If there is something thats bad (remember O2 sensors are consumables) it may run right when you first start up and it's cold, but go to crap once its fully warmed up and running.

[16949]

The boot is hacked to hold right now, and I have to keep fuel level under 1/2 tank to prevent leaking. So until that is fixed, I don't feel full confident troubleshooting as so much was adjusted in the initial fuel pump change. The problem was not immediate after the fuel pump change, but within 100-200 miles.

Right now it starts okay, although it needs to run for a few minutes or seems to want to peter out. I'm not sure that is unusual. Once it is warmed up a little, it driives fine for half an hour or so. I think the timeline is closer to 35 when the a/c is running, closer to 45 minutes if ac is not running but it is hard to be sure of those variables. Somewhere around the 40 minute mark, it will start to act like the fuel pump is failing, it wants to sputter out. If I press the clutch down, rev it higher before letting the clutch out, I can usually "limp" it along for a little while, but very slowly and with lots of "race me!" fanfare. That's the best scenario. Worst scenario is when it bucking bronco'd down the road before stalling out, when someone else was driving it and tried to just quickly disengage the clutch. If it sits for an hour, the 40 minute good driving "clock" resets. If it sits for only a few minutes, the 40 minute clock is maintained.

The only thing I notice is more frequent running of the fan in front and increased frequency of clicking noise from the fuse box as it gets closer to the time where it starts acting up.

I can drive it 40 minutes at a time, every time.

[sdg3205]

My guess is coil too. I had the exact same thing. Coil reaches a certain temperature over time and stops producing enough spark. Car starts bucking like its running out of gas and eventually dies. A quick coil swap is nice and easy to do.

[Nicholas R]

I chased a bad coil for years because of this. I could drive for a little while, but as soon as the engine was really heated up, it would do this thing where you the more gas you tried to give it, the more it bogged down. It was an automatic at the time so I couldn't do the clutch trick. Every time I tested the coil with a volt meter, it tested fine, because the car was usually cold when I tested it, so I never saw anything out of the ordinary. I assumed it had to be something else, so I changed cap, rotor, wires, plugs, fuel injectors, etc. first, with little change. The coil I had was some aftermarket coil from Hervey too so thinking it was (somewhat) newer, I thought it was okay. One day Patrick C had his original bosch coil with him that was still good, and I swapped it in for the hell of it. Made an immediate difference. I actually couldn't believe how quickly it made such a huge difference but it did. I think I ran with that coil up until I did the engine swap.

[sdg3205]

+1 nick!

I even took my tank apart and stuck the damn spring in the pickup hose!

[DMC-81]

Based on Nick and Dave's experience, and your description, I would replace the coil (101052) first then evaluate. Then at least the lambda relay (101071), if not the whole relay kit, and evaluate again.

I can see why you honed in on the relay compartment based on the clicking just before the event happens. I don't know if that is normal behavior with a failing coil/lambda system or not. Perhaps others can comment on that.

Speaking of ignition issues, here's another (non D) story. On my V8 Fiero project I had replaced literally everything in the engine bay, including rebuilding the ignition distributor/coil to an HEI version. There was one little resistor part in the distributor that I said to myself "ahh that still looks good". Then, in my second trial drive, the engine quit, and after 5 minutes, it restarted. I knew exactly what it was. I drove the car straight home and I changed that $10 part. Problem solved.

I know how frustrating it can be to have a car not running right. Let us know how it goes.

[mluder]

Bit of house keeping too...

Step 1: Remove Fuse box cover.
Step 2: Find a safe place to store it.
Step 3: Never put it back on.

The fuse box in these cars tend to run a little hot so most people get rid of the cover to let it breath a bit better. Of course your mileage may vary...

Cheers
Steven