Acceleration problem

[kabmedic]

When I first start the car, everything runs ok, except for the fact I can't get it above 60-70 mph. When the car warms up, it won't accelerate at all unless I pump the accelerator. I have nearly been stranded at several intersections because I can't get it to accelerate. I have tried everything I can think of. Fuel pressure is fine, 29. I believe I'm running too lean because I can open the throttle body by hand and hit it with FI cleaner and it revs up. The only problem is, when I try to adjust the fuel mixture, it doesn't change.
Also, the throttle seems to have a slow response. I tried adjusting the TPS, but no change.
Any other ideas?

[Alfred1]

Have you looked at Brad's D-Jet Troubleshooting page? Here's some more troubleshooting info taken from a VW troubleshooting guide. There's also a picture around here somewhere that shows the (mostly) correct vacuum hose layout.

[Bleyseng]

Check the timing first and make sure the advance plate is moving right.

Geoff

[DJsRepS]

I wasted alot of time and money tracking down the same symptons. Idle poor, poor power but hit all 4 cyl when floored, and any crusing stedy throdle it sounded like **** all 4cyl. Sounded like major ign break dn. There is a resistor in the rotor and plug ends of the wires, MAKE sure you do not have resistor plugs in it. My FLAPS crossed my non resistor plug #'s into resistor plugs twice. that helped but d/n cure. I soldered every rivet in the relay board, I rebuilt the FI harness (found terminal on trigger points green and fell apart and some ground terminals on the block same shape, Still the same In the end unplugged temp sensor 1 at the intake manifold. This mainly adjusts fuel mixture during warmup. I left mine unplugged. Ive ohmed this part in the past it checked ok. Im looking for replacment. Unpluging the TPS is good test but you wont want to leave it unplugged as its main function is an accelator pump if yours is bad your miss should go away but very slugish taking off etc.. If unpluging Temp sensor 1 dn cure yours as it did mine cover all the basics. Pull plugs if 2 are normal burn and 2 dark the trigger points in dist at fault. Adj valves, set dwell, then timing, check dist advance plate lube and drop of oil dn the shaft advance, borrow or but MityVac test tool and check vaccume adv and MPS both should hold vac. It took 2 months of agravation and wasted $$ Plugs cap rotor points condenser wires ETC... Hope you have better quicker fix than I did. I just joined this post to share this as it sounded just like mine. I would not even run mine like that it made me so mad and sad Good Luck DJ

[Scooter311]

Hey this sounds obvious, but what about your throttle cable? Mine started sticking and got hard to pull, then would only pull so far before I realized what was happening. Thought I had a bigger engine problem when it was only a simple fix.
Slow to accelerate, slow to wind up and come back down, only rev to like 2500, etc. Replaced cable, all is good.

Cheers

[kabmedic]

Thanks for all of the advice. I think my engine is running too lean once it gets hot and therefore chokes when I try to accelerate. I'm going to try to adjust the TPS and I've noticed that the pressure sensor has been opened and has obvious screw driver marks on the adjustor. Any ideas how to check that this is at the correct setting? Also, which way do you turn to make it leaner or richer. Same for the control unit. Also, do you think raising the fuel pressure could help? I'm at 29 right now.

[kabmedic]

How do you check that the advance plate is working correctly?

[kabmedic]

OK, here's what I've done so far.... I checked the dwelling, reset the timing and reset the TPS.
Now it won't idle up to speed, the idle adjustment screw doesn't have any effect on the idle speed, when I try to drive it, it is slow to rev up and won't rev above 3000 rpm's and it backfires alot. I tried adjusting the fuel mixture, but noticed no change. It is idling much smoother though. Could it be a bad TPS??? How do I know if it is bad? Everything looks ok on the inside.
I am on the brink of figuring it out, I can feel it!!!

[Dave at Pelican Parts]

The fuel pressure is supposed to be 29 PSI, so that's good.

The adjustment on the ECU is for idle only. CW for richer, CCW for leaner.

Check that you CHT sender is plugged in, and that the readings it gives are reasonable. (Check the Brad Anders page for that.)

You can test the vacuum advance by hooking a hand vacuum pump (e.g., MityVac) up to the advance fitting on the distributor and watching the timing with a timing light. It should advance as you pull the vacuum. The advance fitting is the one pointing away from the distributor body.

The MPS can only be set by using an inductance meter like a WaveTek (which isn't that easy to find or to use) and a vacuum pump of some kind. Or it can be tested by using a wide-band O2 sensor with the engine running. Pelican sells the LM-1, which is supposed to be a pretty good O2 sensor. Read up on Brad Anders' page for what the different adjustments do.

Oh, you also want to check the diaphragm in the MPS. Use that vacuum pump to pull a 15" vacuum on the vacuum fitting. If it does not hold for several minutes, the diaphragm is leaking. Which is not good. If you cannot pull any vacuum for more than a second or two, the diaphragm is completely ruptured, which will make the car run really really really badly--if it runs at all!

--DD

[pbanders]

Regarding the MPS adjustment - I have instructions on my web page on how to do it, but I don't recommend it for most owners. The test equipment will set you back about $200, and it's likely that any MPS that needs adjusting is fairly worn out and bugger'ed already. I suggest buying a rebuilt MPS (~$250) from Performance Products, and if you're really concerned about making it right, get Jeff Bowlsby or Geoff Bleyseng to check the calibration on it for you (for a fee, I hope ).

BTW, the car will run with the MPS diaphragm leaking like a sieve, just runs really rich. I've even started my car and run it up and down the street with the hose to the MPS disconnected! It's more of a challenge to find something that KEEPS the car from running!

[kabmedic]

When I try to set my TPS as suggested by turning it completely CCW and then using an ohmeter to zero it out, I don't get any reading at all until about halfway at which point it is at zero. Is this normal, or is my TPS shot?

[Dave at Pelican Parts]

I believe you're checking the wrong pins...

--DD

[DJsRepS]

As said by me and others as a test of the TPS just unplug it and drive it once. It will be slugish throdle responce but if it still Backfires it aint the TPS. Look elsewere, look above at my prev reply. As a test try a drive with the intake temp sensor unplugged as well. Good Luck DJ in Fla.