Power Loss??

bob174 · 04-28-2003, 10:17 AM

I have a '73 2.0 with the injection. The engine runs great. However, after I've driven it for 30 minutes, and it's good and warm, I notice that it just doesn't have the same acceleration as it does before it's warmed up. It seems to show up, for instance, after I've driven on the freeway for a little while, and I come off the freeway and sit a light for a couple of minutes, or after I've been in stop&go traffic. After this, it's difficult to pull away from a light without getting the engine to about 2000 rpm before engaging the clutch or the engine will bog. Also, after you get going, it just doesn't have torque that it does when it's cold. One thing I've wondered about is whether the fuel pump could be getting hot under these stop&go conditions and could I be getting a little vapor lock? The fuel pump is in the original position. I've replaced all vacuum lines within the last 6 months, the timing in spec, pulls hard (for a 95hp engine) until it gets warm, and I've sat at idle for while. Even after this problem occurs, the engine still runs well--sounds good, no missing, etc., just a power loss. Any ideas?

chrisreale · 04-28-2003, 11:24 AM

Check your CHT. Should read less than 100 ohms (if i recall correctly) when fully warmed up. Use a multimeter, positive connected toi the CHT, neg to the neg battery terminal.

bob174 · 04-28-2003, 11:57 AM

Is there a particular resistance, or is anything less than a hundred ok?

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Pretty much anything under 100 is OK. Check the CHT info on Brad Anders' D-jet pages: http://members.rennlist.com/pbanders

Check the fuel pressure when the car is doing this. (I have a pressure gauge permanently installed, now.) If you have the full 29 PSI when the car is misbehaving, then vapor lock isn't your problem.

--DD

bob174 · 04-29-2003, 06:28 AM

I was checking out Brad's page, and it looks like I also need to check the resistance of the ballast resistor. Where is that thing located? Also, does Pelican have a permanent installation fuel pressure gauge setup?

norustscott · norustscott's Garage

The less than 100 ohm spec is for the sensor. Keep in mind the ballast will alway have 270 and will add to the amount read by the ecu...

Dave at Pelican Parts · Dave at Pelican Parts's Garage

The ballast resistor, if present, plugs into the wire coming off the CHT sensor. The other end of the resistor plugs into the wiring harness, at the connector where the CHT sensor would plug in if there weren't a resistor.

--DD

bob174 · 05-06-2003, 05:34 AM

I finally had a chance to put an ohm meter on the CHT last night. It ohmed out at 1220 ohms at about 80 degrees. Based on the information on Brad's page, it seems to me that it's the early part number CHT. I could not locate a ballast resistor anywhere near the CHT.
1) If there is no ballast resistor installed, would this configuration result in the performance issue that I spell out above?
2) Is there anywhere else that I should look to ensure that there is no ballast resistor installed?
3) When I install the missing resistance, is there anything that I should expect to have to adjust, such as the idle?

mike_the_man · 05-06-2003, 06:24 AM

Just another thought:

Check your MPS to make sure that it holds vacuum and that the resistance in the coils are correct. My car was doing the same thing as yours, and it turns out that the MPS was toast. Just one more thing to check.

Good luck,

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Sounds like your CHT is fine, or close enough, when cold. If it measures under 100 ohms when hot, it's fine.

You're most interested in what happens when things warm up, as that is when the problem occurs.

--DD

bob174 · 05-06-2003, 08:57 AM

Right, Dave, but there's no ballast resistor that I can locate. Based on Brad's site there should be a ballast resistor in the loop... Which there is not.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Take a look at the spark plugs after the engine has warmed up and idled for a while. If they're black and sooty, then a ballast resistor isn't going to solve your problem--and I bet they are... It sounds to me like you have an overly-rich mixture; more resistance in the HTS circuit will richen it more. The whole resistor thing is a red herring, I do believe.

What's the resistance of the sensor when the engine is warm?

--DD

Bleyseng · Bleyseng's Garage

I thought the ballast resistor was to help set the cold idle and warm up so that shouldn't have anything to do with your problem.
Hot power problems could be a MPS going out so it is going rich the warmer it gets. Check with a vacuum gauge for leaks.
If it not a going rich problem then look at a clogged fuel filter, pinched fuel lines.
How is the timing? Does the mark bounce around or blur when timed with a light? Could be a dizzy problem, worn shaft or FI points.

Geoff

chrisreale · 05-06-2003, 05:00 PM

I thought the Ballast Resistor was to richen it up at throttle???

Bleyseng · Bleyseng's Garage

No, it is a band aid since the new 2.0L ECU wasn't done. Using the 1.7 ECU they needed to richen the idle with the CHT so they added a resistor. Undo the resistor, the car will still run fine, the idle is off at warm up( notice the hunting that occurs).
Geoff

bob174 · 08:45 AM

I do get some hunt during warm up, but after running a few minutes, it's idle is rock solid. I'll let you know the CHT resistance at normal operating temperature. Brad's description of the failure of the ballast resistor in a shorted mode (which would be the same as not having one installed) is this:

Shorted: Eliminates bias from head temperature sensor. Causes leaner mixture across full range of operation, resulting in drivability problems, possible backfiring. Check with an ohmmeter.

I will install a ballast resistor, and if that doesn't cure it, then I guess the next thing to check would be the MPS...

Dave at Pelican Parts · Dave at Pelican Parts's Garage

The ballast resistor is a red herring, until proven otherwise. Check the temp sensor's resistance when the engine is warm. Look at the spark plugs. I am almost certain your engine is not running lean; I think it is a rich condition when it is warm.

--DD

bob174 · 05-09-2003, 03:29 PM

I ohmed out the CHT hot and it was 29 ohms. Also ohmed out the MPS and the coils were close to the published specs, although not exact. I need to get a hand vacuum pump to check the condition of the aneroids in the MPS. What else could I look at?

scotty914 · 05-10-2003, 05:14 PM

my fuel return line was clogged and it would go nuts after a run the sitting at idle i would have to rev it to keep it from stalling it got so rich with higher pressure
then it would stumble off the line for 30 seconds or so till it dropped the pressure back down
check fuel presure

Bleyseng · Bleyseng's Garage

A vacuum gauge will check out the condition of the diaphram in the MPS not the aneroid cell. Those things never go bad but the diaphram sure does as it cracks at the edges.
Geoff