Jfrahm

Hi all,
I am frustrated by my brother's old S4 which I am trying to get running decently to put up for sale. This problem is new. The car will not start when cold cranking without a squirt of gas or starting fluid. Once it's been started it will idle and run OK and restart. It's a supercharged (Murf Stage II) 1987 S4 5 speed.

Symptoms:
No injector pulse that I could see with a multimeter connected to an injector wire. Injectors are Ford E9A 30lb bosch red top.

Temp II measures 7.7K ohms, a bit high for 45F coolant.
I measure 3.4M from the TempII connector back to the harness (does not seem shorted or open).

Front knock sensor wiring is in poor condition, disconnecting it does not help (That is, if the 3 wire connector with a gray jacket running along the LH (throttle cable side) is the front knock sensor).

Cam sensor wiring is in poor condition, the pins came out of the connector but I believe I have them reinserted correctly but this could be an issue. I am not sure how to verify the cam sensor connection but I recall reading that there were running/driving issues if the leads are reversed. Will it run with the cam sensor disconnected?

Disconnecting the MAF does not help.

Fuel rail pressure is 20 psi cranking and typical when running, I do not recall exactly what the pressure is but I recall checking it and checking the spec and being satisfied.

Plugs are just now clean but get pretty black once it is running (possibly due to running w/o the blower hooked up?).

I have normally been working on this with the intake from the blower to the MAF off and the water-to-air intercooler off as it's in the way. It might improve the problem slightly to have these bits back on, but it's not obvious.

Any suggestions?
Thanks,
-Joel.

John Speake

3.4 Meg from temp 2 plug back to the LH ECU pin13 ?

Jfrahm

I just measured across the connector at the Temp 2, mainly to look for short or open. I did not ohm the harness back to the ECU.

Lizard928

If the problem was the temp sensor it is more likely that it would still fire the injectors some.

I would check and clean all the connections at the battery, and then clean the grounds at the back of the engine block.

fraggle

Note: there is no specific separate "cold injector" as there is in older systems on the S4.

Is the tach moving? I had a problem on mine where the cps wiring harness wore through and would short to the block, making starts tough but not impossible.

Mrmerlin

Joel since you have now identified some failure issues your going to be chasing your tail till they are fixed properly.

The knock sensors the CPS and the cam position sensor should all be replaced before you continue trying to get the engine running.

The temp 2 sensor should also be replaced and the connector that goes to it swapped out for a fresh connector,
solder the new connector to the old wires that you have cut back to find fresh wire on the car side of the harness.

Also consider swapping in a fresh MAF and a factory O2 sensor

Jfrahm

Thanks Stan yes I will work on some of these things. The Temp 2 seems OK, I measured it properly this time and the values are OK for the current temp. I would think it'd start and run with the hall sensor disconnected and likewise the MAF or knock sensor. I'd like to get a handle on this issue so I can move the car around. It is kind of in the way.

The MAF, I do not have a spare ($$$) but my understanding is that if it's bad the car will start without it if it is disconnected.

The tach bounce is the same as on my other 1987 928S4, which starts and runs great.

I want to get a better look at the injector signal, I have not detected it but I also have not taken the fuel rail covers off a running car to see what a working signal looks like. I want to verify that I do not have an injector pulse at cold cranking.

-Joel.

John Speake

The injector pulse is very short - typically around 3mS while cranking.....

outbackgeorgia

The connector to the CPS is suspect for the symptoms you describe. The knock sensors will not prevent starting as far as I know.
I just soldered the wires bypassing the connector for a fix. This conector is simply critical to an S4.
Also, on the Temp II, the measurement is from each pin to ground, NOT across the two pins on top of the sensor. There are two separate resistors In the sensor body.
Have fun!
Dave

Jfrahm

Thanks Dave,
I can check the crank sensor but I have no reason to suspect it. I have a good tacho bounce and the car runs fine if you get it started. The crumbled connector in my case is for the cam sensor. I will get it sorted. I am not sure if that is what you meant but my understanding is that the car should start and run without it.

I realized my error with the Temp2 yesterday and re-measured to find it is in spec. The near-term goal is to get it to start on command so I can move it in and out of the garage, etc.

Thanks,
-Joel.

outbackgeorgia

Joel,
Correct, the cam sensor and knock sensors will not prevent starting, I would look elsewhere. For example, fuel pressure seems low for an S4, (stock should be about 38 psi) but I don't know what it should be for a Murph supercharged engine. However, if it is low or 0, it may have an issue. It may be leaking down. A typical fuel pressure check valve issue is the symptoms you describe. Won't start cold , but runs and restarts once it 's running. I put a gauge on my rail to test, monitor. Try jumpering the fuel pump relay so it can pressurize before attempting to start.
Good luck!
Dave

dr bob

Go after the low fuel pressure issue. The pressure after pump run but with engine off needs to be enough to push fuel into the engine. A cold engine adapts to increased fuel needs but low fuel pressure will keep it from starting. Possible causes include a tired fuel pump relay, loose or corroded power supply wire from the battery, weak pump, dufo pressure regulator. Not necessarily in that order. Start with the cheap/easy stuff before you spend heavily. The fuel relay is an instant replace item regardless. You'll want to disconnect the battery to remove and replace the old one, so it's a few more minutes to pull the spare and get into the battery well. In there you'll see a few smaller wires piggybacked onto the positive terminal connector. With ground strap lifted, take the positive assembly apart completely. Clean each connector on each wire carefully, so there's shiny metal showing. A brass detailer's toothbrush is good, working to kepp the tin plating intact on the ring terminals. That's two down. Next is a vacuum test on the diaphragm side of the regulator. The FPR is behind the passenger-side head, under the lower air cleaner housing. MitiVac to test for leaks. Do the two dampers while you are there, but they don't manage fuel pressure.

You'll need to fix the wiring issues, but if it runs after the spritz of fluid, those thiungs are not your starting problem.

Jfrahm

Thanks! I just now built a Noid light and when it was pretty dark out I could see a faint flicker from it when cranking so I probably have injector pulses. I tickled the fuel injector harness to dump some fuel into the intake and it fired right up with the Temp2, front knock and cam sensor disconnected.

I am not sure why the fuel pressure is low but consistently 20 psi at cranking and with the key off, I suppose it could be the RRFPR but the stock FPR is in place and when it's running I see high 30 psi. I had the injectors off on the RH bank and they were all fine and dandy but one could be dripping on the LH side I suppose. The throttle assembly is in the way of easily pulling those.

Engine vacuum is not great at like 12 in.-Hg but I am at over 5000 feet.

I will try jumpering the fuel pump relay and see if it'll cold start, and clean up the positive terminals as you suggest. If a damper had failed I think it'd pee fuel into the vacuum system but I can check those eventually.

-Joel.

dr bob

You are correct about damper failure modes. Fuel into the vacuum system would give you an opposite symptom, where ading that initial squirt of fuel would make the problem worse rather than better.

Poor manifold vacuum is a symptom of cam timing and/or ignition timing problems, and may also be related to a large vacuum leak. But that would also make fuel pressure higher rather than lower, so moves off the immediate list except for the part about needing even more fuel to mix with the leaking air.

Let us know what you find.

Jfrahm

Still no improvement.

I pulled the LH fuel rail and cleaned those injectors, I'd done the RH side earlier. The injectors seemed fine, worked OK, I got a trace of fine coppery dust out of them when backflushed and that's the same as I'd seen on the other bank. It is a very small amount of very fine dust and only visible as I backflushed the injectors into a fold of paper towel.

Fuel pressure might be a bit higher, or possibly I am going around to look at the gauge more quickly. It drops slowly after cranking.

Jumpering the fuel pump relay gets me 48 psi (indicated) at the rail but still no cold start. Fuel pump relay is the wrong part (standard #53)

I *suppose* it might not start cold without the air from the supercharger but that seems thin.