Big Ride, now Big Headache = Mad Souk!!! -> Help!! Please! JW?? Ron?? Warren??

MotoSook · 07:22 AM

I notice my car acting a little funny last Sunday coming home from the track. We were stuck in traffic for over an hour while it was raining off and on (sometimes hard rain). It started to idle a little rough, then I noticed it was not as powerful intermittently.

I have a 78SC motor with Magnecor plug wires and NGK plugs.

I swapped a different CDI box, changed plugs, dist. cap and rotor. Both CDI boxes whine as they should, plugs were tan-ish as they should be.

I thought the rain may have done something to the ignition, so I attacked it. No dice!

I drove the car to work yesterday, and the behavior was the same, less power above 3500RPM than before, and it was neither snappy nor powerful as before. I can rev it up to redline with small throttle opening. At large throttle opening, it bogs down. (kind of like my carburated motorcycle when it is cold or I forgot to turn the fuel valve to on....no gas)

On the way home yesterday, I stopped to fuel up thinking I might have gotten bad gas, so I added fuel from my usual station. While the gas pump was running I checked that the fuel relay had not worked itself loose. Nope, not loose, but a bit warm, not hot, warm. After I fueled up, the car would not accelerate with anything but with a crack of the throttle. I could have bear-crawled faster from a stop than the car would accelerate.

So I stumbled home, check CIS fuel pressure.

*system pressure =~ 71 PSIG

*control pressure -=~ 71 PSIG! WTF!

My WUR was probably plugged and not bleeding pressure as it should. SO I swap it with a WUR from an 80+ car's CIS. And the control pressure dropped to 51 PSIG. I know, the WUR is not a 78, but the pressures-vs-temps are about the same for the two, esp. when fully warmed up. SO I figure it will do until I get a correct WUR.

I fixed the control pressure problem, but the power and bogging problems persisted. So I changed the coil, checked grounding in the engine bay…no change!

Timing is at 12 deg. Advance, and the dist. does advance to 30+ as it should when I idle in the garage.

Thinking it might be sticking, I pulled the distributor to check and lube, gave it a healthy bath of WD-40, spins freely. Re-install. Still nada! I noticed the trigger wire from the dizzy was not so healthy; the insulated conductor had cracked insulation so it might have been shorting out with the un-insulated lead. I wrapped it up nice and still no change.

Pulled the CIS boot and there was no indication of any problems there. Air sensor plate moves freely.

Things I have not done: change fuel filter, swap fuel pump relay.

What I’m I missing? I know I can get pressure yet not have adequate flow, so I’m going to swap the fuel filter today.

I’m scratching my head and throwing tools gang…HELP or I’ll have to drive the Cherokee to New Jersey..yeah FUN! Not!

And 19 mpg at best

MotoSook · 08-08-2003, 07:03 AM

One more thing, in case you are wondering, the cold start circuit and pressures with the 80+ WUR seems OK. I did not put a gauge on the system, but this morning I started it after it sat all night, and the start sequence seems OK. It idled high and slowly feel down to normal. So I have to assume the control pressure was rising as it should.

1fastredsc · 08-08-2003, 07:06 AM

Hmmmmm, well the fuel mixture is obviouly not right, especially if it idle fine than gets testy under load. Definitely replace the wur as i believe the wur from the late cars are a lot different than yours. But while your doing this make sure you check for vac leaks and things of the such. And GL!

MotoSook · 08-08-2003, 07:11 AM

The graph for the early 78 CIS pressure and the 80+ CIS pressure versus temp is not that different. Warm control pressure ranges for the two over-lap with the 80+ pressure being about 2 PSI higher. The range of control pressure for the 78 is something like 45-52 PSI, and I ran the car witht he fuel gauge connected last night., The control pressure was a steady 51 PSI, even after I went for a drive. I left the guage in-line and checked it when I got out of the car, 51PSI.

So under warm conditions, there should not be such a difference in the two WUR's control pressure to make my bogging and lack of power an issue, right!?

MotoSook · 08-08-2003, 07:14 AM

I plan to do the carb cleaner spray check today, but I can tell the engine is sucking air at idle through the idle screw and air sensor plate, because I can see the CIS boot compressing. When I rev it, the boot relaxes and when I slightly push up on the a-r plate, the boot relaxes, so it would be a small air leak, if there was one, not big enough to make the car run like that, right??

AFJuvat · 08-08-2003, 07:15 AM

I've seen something similar on older cars as well. Was a shop queen for a week swapping and testing parts - symptoms were the car leaned way out under throttle (no power)

One other symptom (which you are not suffering) is that the car would be fine right after startup, but would get progressively worse as the car ran.

Ultimately, it turned out that rust in the tank was clogging the intake.
Might be something worth taking a look at.
My 2¢ YMMV

AFJuvat

MotoSook · 07:25 AM

It feels like I'm not getting enough fuel or the exhaust or intake is blocked. Ever have a cat plug up on you? That's the feel of things, but I don't have a cat (Dansk pre-muf with stock exhaust).

I was going to change the fuel filter last night, but it was 1AM and my neighbors go to bed at 8:30..the whole sub-divsion!!, so I didn't want to continue pulling in and out of the drive way.

MotoSook · 07:25 AM

Juvat: I changed the tank screen a year ago. The entire fuel system from the tank screen to the fuel dist. is less than 16 months old. Good thought though! Thanks.

cstreit · cstreit's Garage

Souk,

Is there any way to watch the pressure at high RPM's. After we talked last night I got to thinking about the pressure vs. volume thing. Why don't you hook up the fuel pressure guage and rev it quickly up to 6000 a efw times and see what the pressure drop is...

If a fuel line/filter/screen were partially plugged, it would show these sort of symptoms... Fine pressure, just no high-end flow...

Early_S_Man · 08-08-2003, 07:35 AM

Souk,

I believe the CDI unit is not the problem. CIS problems may be making the problem worse, but the fact that the initial problem came about in rainy conditions leads me back to ignition ...

Most likely problem is the green coax cable from the distributor ... when the outer insulation is cracked, there can also be cracks between the inner insulation and hence, voids, between the center conductor and outer braid shield! Putting an ignition 'scope' analyzer on the ignition would tell you for certain whether or not the output from the CDI-system is erratic! Wiggling the green coax cable with the scope on the engine would tell you if can induce missing by flexing the cable or spraying tap water on the cable.

If you know anyone with a traditional oscilloscope and a tach/dwell meter with a clip-on tach pickup probe ... that clip-on ignition probe can be hooked to the input of an oscilloscope [terminate with a 50 Ohm or 100 Ohm resistor at the amplifier input jack] ... to give you a 'poor-man's' ignition scope ... use probe on distributor center lead, and adjust scope time-base until six - twelve ignition pulse are present on screen.

MotoSook · 08-08-2003, 07:36 AM

Chris, I did that last night. Although I did not get it to 6000 and sustain that, I blipped the throttlr a few times to high revs, and the control pressure was steady at 51 +/- 2 PSIG. It'll be easy to try your suggestion.

MotoSook · 08-08-2003, 07:40 AM

Warren, thanks for jumping in. I don't have a scope nor have access to one, but I can run a continuity test on those leads right? When does the coax go after it leaves the dist.? I'll look at the manuals, but if you can tell me, it'll save me some time. Thanks.

pbs911 · pbs911's Garage

Ignition. Do what Warren suggests and change the plugs. Just because the plugs look tan, doesn't mean they work well.

Early_S_Man · 08-08-2003, 07:52 AM

Souk,

The green coax runs directly to the six-pin connector of the CDI-unit. Resistance of the pickup coil should be 600 Ohms +/- 10% at terminals #7 and #31d on the diagram below:

MotoSook · 08-08-2003, 08:03 AM

Great! Thank you Warren, I'll check this when I get home. If that is all, I'll just homey rig it! (crossing figures!)

cstreit · cstreit's Garage

Souk,

Remember I have a spare one that you can borrow. I'll dig it out in case you need it.

Chris

MotoSook · 08-08-2003, 08:10 AM

Chris, a spare ____ ?

island911 · 08-08-2003, 09:07 AM

Quote:

Originally posted by Souk
It feels like I'm not getting enough fuel or the exhaust or intake is blocked. Ever have a cat plug up on you? That's the feel of things, but I don't have a cat (Dansk pre-muf with stock exhaust).. . ..

Clogged exhaust (Cat) is what I was thinking. The pre-muf's do have internals. . . though i've never heard of them coming loose.

A plug wire (coil) with worn insulation (rubbed down, thin) will make a similar rumming engine. .. . at idle the spark jumps the plug gap w/o problem; under load, the cylinder pressure goes up and the spark prefers the worn spot on the wire.

(in a rush -- sorry if this was covered already)

MotoSook · 08-08-2003, 09:14 AM

Hi island. All my plug wires look good (1.5 yr old magnecor), but if the trigger wire check doesn't turn up anything, I'll check the resistance in all my Magnecor wires. The Dansk pre-muff is new, just installed it last week before the DE. If the internal came loose, it would probably not cause much of a restriction as the internal is perforated. The pulses from the tail pipe at idle seem to be normal and the idle noise/sounds all seem to be normal. BUT! It'll be checked too if the trigger wire test doesnb't reveal anything.

Thanks.

rlane · 08-08-2003, 09:31 AM

perhaps a little far fetched but I had experience (and have seen several other threads from similar questiions )where it is a fuel pump issue..maintains pressures ok without a load (mine ran fine on flat Interstate) but under load (a hill...acceleartion) it would stumble , lose power etc. Try switching to a friends fuel pump and se what happens?
Richard