onthedge928s4

dear 928 owners,
I have a 88 s4 that just started being picky.i came out one day hard start . 1 or 2 try`s. then i try another time starts right up.then one day i try and crank it wants to start ,but as soon as i tap the gas she dies?then it may sputter like on 2 or 3 cyl then die before ir smooths out.it had a fuel pump filter an fuel control unit last year i check the fuse to pump, swap a relay no change in start characteristics.have any ideas ,but when she finnally starts runs ok???you have fuel press specs. running and standing....bleed down times ??
could the ign control unit be going? coil?pump??
i would appreciate any input???
thanks bob

John V

I'm no expert but I would think all your concerns are possibilities.

On the plus side, if it runs good after it starts, you can rule out majors such as compression, valves or timing belt.

That still leaves many possibilities. I'd start with basics of fuel and ignition system. I have an older model and mine has had all these symptoms. I found I had a bad coil and marginal fuel pump. ON yours, I'd be real careful on the electronics side as I've read you can easily damage the electronics during diagnostics if you don't know how to test properly.

Have you confirmed fuel pressure and injector firing? Have you confirmed spark?

Incendier

I'm no expert either, but during my diagnosis of the problem in the below thread "shark bog", my '83 exhibited the same symptoms. Mine were elecrical/connection problems.

Ken Postma has a decent electrical diagnosis for the LH <a href="http://members.prestige.net/jpirtle/keepers/fi/lh_troubleshooting.txt" target="_blank">here</a>.

If everything mechanical checks, I'd try there.

Good luck

Donald

Bob-
You didn't mention how long the car sits when this happens- IF it's only after extended "rest", sounds as if the fuel system is bleeding down. Isn't there a check valve near the outboard fuel pump?
Good luck
Donald

Incendier

To add to that...yes, there is a check valve. On the pump side (not the feed side) of the pump between the pump and the filter.

I believe the test for the check valve involves bumping the starter several times (to get the pump to cycle) before acually cranking it to start. If it starts, the check valve isn't holding pressure in the lines.

Or just jump #30 and #87 of the relay points to get it to run all the time.

Easy replacement once the pump is dropped.

onthedge928s4

good feed back people,
the car does not matter
how long it` rested. one thing i forgot to mention i had ran the tank low a couple of times prior.so i have been filling it full lately.i also check the temp sensor for the control unit.
i haven`t jump the fuel pump relay yet.i remove the connactor on the temp sensor no corroision present..i can check fuel pressure.any one have a safe way to test spark!also is that a temp sensor on the top rear of the intake?how can i test it?i also check to see if the air mass meter was clear that was ok.also sometimes when it cranks it sounds loud or hard to crank and then just starts.
timing issue?????cam belt just done???you guys are doing good keep the info coming and i`ll let you know how it goes.
robert

Thom1

Hi Bob,

I don't know that those symptoms fit the following scenario. But, the document covers some periodic maintenance issues that could help:

Starting Problem:

When I was fixing valves, the most suspicious thing I found was a broken coil ground cable. Now that I am back up and running, there is no more starting problem. Here is what I did, and you can do: Clean the distributor cap and rotor contacts with a point file. Check or replace 2 coil ground cables. (Right side cable goes from coil bracket bolt to topmost front timing belt cover bolt. Left side connects at bottom rear of back timing belt cover.) Check engine ground wire about a foot forward of firewall, and a foot deep on right hand fender well. Scotch Bright all male blades of engine compartment electrical connections. Cycle blades in and out several times to clean female sides. A small round file works on some round female connections. I sealed ignition wires and distributors with Coastal Ignition Sealer from Autozone. Check their condition before you pull all the wires – too much work. I saw an ignition wire tester at Autozone. Clean your battery terminals… Believe it or not, that can be the culprit with no crank sound.


HTH,
Good Luck,
<img src="graemlins/jumper.gif" border="0" alt="[jumper]" />

Incendier

I'm going to follow up to a private message here because I want to make sure my math and physics are right.

The link above in which I referred to the Ken Postma keeper ends with Ken saying that his problem was that the resistance was .3 across the harness (harness less 1 injector). The question to me was "so, what was the problem then", which is a fair one. Let's see how well I remember electrical junk.

Here's my take on this:

As I recall, resistance for a parallel connection is the "reciprocal of the reciprocal", i.e. decreases with each additional "resistant object" in the circuit (series, I believe, is additive).

Ken was saying that with one injector out of the loop and the rest in, i.e. measuring at the injector plug and not the injector itself, the combined resistance of the system should be +/- 2 ohms, which is 7 injectors at 15.~ each, in parallel. I presume that the LH system uses high-imp injectors as opposed to the L low-imp ones.

Since he came up with .3 ohm total resistance, this takes me to three possible conclusions.

One, that the _each_ injector had a resistance of 2.1 ohms; two, that one or more injector was offering no resistance, or three, that there was an open in the wiring harness which was taking one or more injectors out of the loop.

From personal experience, if the ground is bad for a bank of injectors there will be no start. Since he was measuring the harness terminals, which - if I read my electrical system diagram correctly - are a send & return positive connection which the computer completes to ground to cause the injector to fire - my SWAG is that an open here would also cause a defect in the system significant enough to cause a no-start condition.

Ken's ultimate solution was unclear.

Can anyone verify or criticize any of the above?

Crow happily eaten here.

Thanks.

John Struthers

Bob,
Let me toss a dime in here.
We have had a bunch of intermittent start posts over the last couple of months.
The majority - not all - were related to coil, coil relay, coil ground. A few to fuel issues
Check out the Greg Nichols site for similar posts and cures.
Check the Archives and remember that Coils do not necessarily fail all at once... they often do but that data is not carved in stone. The coil zone is by far the cheapest and easiest IMO to remedy.
Do not trust the OHM METER ON the coil... once that puppy starts working under load things change ...check the relay, swap the coil if all else fail you have a spare (or two) coil.
John S. and Pattycakes

onthedge928s4

applause ,
I`m still looking ,but i ran the car fuel tank low so i added some techron filled the tank and stomped on it for a few days.It`s getting better but i still get one now and then ???i checking those grounds too and cleaning them
thankyou all