1.7l D-jet firing on 1/2 the injectors...

MarkRobinson · 07-16-2007, 11:43 AM

Ok, my engine is back to running on 2 cylinders.

A month ago, I had the same issue: very weak spark on 2 of the cylinders, then cleaned the grounds & the problem was solved.

Last week, same thing. Car ran on 4, then on a restart (after I stopped off at the gym), only runson 2 cyl.

Re-cleaned all of the grounds, verified no voltage (noid light) on the two suspect injector harness connectors.

From a diagram I saw online this weekend, I suspect one of the injector drivers as if one of them failed (there are two), it would take out the two cylinders I"m having issues with.

How do I test to see if this driver is indeed dead? I plan to check resistance from the driver through the harness to the connector too (this week).

Mark

bowlsby · 07-16-2007, 12:49 PM

Which two cylinders are not working? Depending on their grouping:

Pairs of injectors share grounds, so if its cyl 1+2 or 3+4, check their common grounds at the center rear topside of the engine

The trigger points control pairs of injctors in another way, so if its cyl 1+4 or 2+3, then your tripgger points are not firing the injectors.

Very unlikely its the ECU.

MarkRobinson · 07-16-2007, 01:00 PM

Well, I've cleaned the grounds 2x, last time, I took the 3-pole copper tab off the bolt off the top of the engine, hit both with a wire-wheel (dremel), & cleaned the tabs with a wire brush, brake-cleaner, & pinched them down for a better ground, cleaned all the other grounds, all relay contacts (just in case), still only 1/2 fire.

I also pulled the disty, then the trigger points: visually look fine, washed them hard with brake cleaner, & re-installed. I have both a used computer & wiring harness on the way: I'm hoping it's one of those.

Now, the trigger points are installed at the base of the distributor: mine were clean as they came with a rebuilt disty I had recently purchased. I could always swap in my old trigger points, but it appears there's not much to fail except when excessive grease/oil is introduced. Correct?

Mark

Tobra · Tobra's Garage

Wrong pairing of the ones working for trigger point failure. As above, ECU is unlikely to fail, pretty simple.

Try comparing driver that works with one that does not, same resistance I mean, could be failure in harness too.

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

Note that the ECU controls the injectors in the same pairs as the trigger points.

Since it's 3 & 4 that don't seem to be working, I would check your fuel filter and fuel tank. Those are the first ones to see fuel coming from the pump, so they tend to be the first ones to get plugged up with crud when your tank has sediment in it.

That, and the grounds. Re-re-re-re-check those puppies!!

--DD

MarkRobinson · 07-17-2007, 05:51 AM

I don't think it's 3 & 4. It's the injector closest to the left rear of the car (by the fuel pressure regulator), & the injector closest to the front right of the car (by the battery).

Fuel filter only has about 400 miles on it, I had replaced it a month ago trying to figure out why my injectors weren't firing at that point. I have no more grounds or contacts to check or clean.

I ordered another computer/wiring harness & will re-tackle this over the approaching weekend. Weeeee.

hardflex · 07-17-2007, 07:02 AM

you can swap out the injector plugs for the sides to see if the problem moves when you do that. Moves, it's the electric signal, doesn't move, likely plugged or bad injector.

MarkRobinson · 07-17-2007, 07:05 AM

I'm way past that: no voltage at the injector plugs for the 2 cylinders not firing.

The car runs on 2 cylinders & has adequate voltage to the running injectors for those two clyinderes, but no voltage (noid light) on the plugs where the injectors are not firing.

If I swap the good running plugs to the other injectors, they will fire too & the car will continue to run even though the fuel is not timed correctly (like a carburetor)

hardflex · 07-17-2007, 07:19 AM

as I recall, when that happened to mine (same 2 cyls poor idle) it was the trigger points. The pad that runs on the cam gets worn, the points close more and more until they don't open so no signal to that circuit. that, or possible the wire connection from the trigger points to the ECU is broken between the Dizzy and the ECU and you'd get the same effect.

MarkRobinson · 07-17-2007, 07:34 AM

My trigger points are newly-acquired as they accommodated my rebuilt distributor, but I can always plug in my older trigger points as I salvaged them before I turned in my old core.

Thing is, I had this same problem back a month ago: running on 2 cylinders. Cleaned the grounds & wiggled wires, it ran, ran great for a month. All of a sudden, it runs on 2 again with no voltage to two of the injectors.

Not sure the trigger points would fail like this, but a poor ground or failed electrical component might. The ONLY thing I did between running good at 5:30pm & running on 2 cyl at 6pm was that I cranked it with one spark plug lead not connected (as I planned on checking two plugs but forgot one due to the heat of the day).

With less than ideal grounds, I figure i might have caused a voltage spike that damaged something in the ECU, has it's had two dead cylinders since then.

I did remove the ecu & harness, & clean all contacts thoroughly in the harness & replaced it all, going through the grounds all over again. I hosed the trigger points down with brake cleaner, expecting to see excess lubricant splattered all over the place, but I didn't find such mess.

I'll swap in my other trigger points tomorrow night to see if that does any good...glad I kept my old set.

Mark

bowlsby · 07-17-2007, 12:09 PM

Have you also checked the continuity on the trigger point wires in the harness? A circuit could be open or even shorted.

MarkRobinson · 07-17-2007, 12:14 PM

very possible, on my list of things to check too. Thanks for the reminder.

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

OK, it's not 3 & 4; it's 1 & 4. Definitely suspect the trigger points, the wiring from those to the ECU. The ECU itself is a lesser suspect; they typically don't fail, and when they do they more usually won't turn the injectors off, rather than not turning them on.

You can look into the D-jet tester that Pelican has; I think we still rent it out. Or talk to the local 914'ers about borrowing an ECU you can swap in.

Or talk to Jeff B about getting a "reubuilt" (I still say that 99% brand-new parts is more than just "rebuilt", Jeff!) EFI wiring harness...

--DD

MarkRobinson · 07-18-2007, 06:09 AM

Thanks Dave, Yes, I remember on the diagram that it the two non-firing injectors were goverened by that same driver.

1.5 months ago when I was having similar issues, cleaning the grounds allowed for the restoration of proper voltage to open the injectors: I was about 3-4v at the time & the injectors wouldn't open via the harness plugs.

I have a used harness & used ECU coming already (ordered on Monday) to test this weekend.

OH! I I found my 3k idle problem: the new hoses on the intake runners at the intake manifold were just barely "roomy", so I had loosened one of the clamps to allow access to install my rebuilt TB, & had never re-tightened it back up. what dork.