1988 924s

Hey Porsche family! The past three weeks have been rough. I have been pulling my hair out trying to figure out why this 60,000 mile 924s will not start . I have been driving this car for the past year now as a weekend driver and it has never NOT fired up and started. Besides running somewhat rich I never had any issues with this car. Last year I had my local Porsche shop change all my belts and pulleys including my timing belt. Also, a refurbished AFM was installed. So to make a long story short I am trying my best to avoid having to bring this thing to the shop as well all know it can get pricey and bringing it to a shop is my last option . SO here is what I have checked and done.
. Fuel pressure at rail is around 36 psi when cranked DME relay jumped fuel pressure psi is around 38-40 psi.
.Tank drained and througly flushed and added 5 gallons of Shell V Power gas
. Car DOES briefly " catch" or run when starting fluid is sprayed into air box.
. Changed all 4 fuel injectors with proper spec brand new injectors and watched them all spray before putting the fuel rail on.
Before I installed the new injectors the car would not catch at all unless ether was used. Now with the new injectors installed the car rumbles up every time like it really is trying to start . It will turn over and catch , and kick but just will not fully start.
.Changed all four spark plugs, and properly gaped them all. Checked for spark at all Four plug wires and spark WAS confirmed by using a spark tester light.
.Noid light shows proper signal at all 4 injector harness.
.I Do have tach bounce.. Wires for the speed and ref. Sensors do look funky though, one appears to be frayed. Seems like Speed and ref sensors are not my issue because I do have spark and tach bounce.
. checked for vac leaks by visually inspecting the lines and did find one line connection off. Connected it back, car still docent start.
I am stumped and at a loss here. Could this be a ground issue? Weak spark? It seems like I am having a issue with fuel delivery but just can't seem to fig this one out.. Its driving me crazy and I can't sleep BC I stay up all note studying and reading up on things no start related.. I guess my next step is to clean all grounds. How important is the ground that connects to the firewall from the battery? It seems to look very croded and sprayed with flex seal as I was stopping a slight leak that I was having from my battery tray. Anything, and I mean anything will be looked over and taken to considered. Thanks guys , it means a lot to me that you are willing to help!

1988 924s

Two things I forgot. I passed the fuel pressure leak down test via Clarks
compression was 180 in three cylinders and 190 on another

tempest411

Have you removed the boot betwen the AFM and the intake and checked for cracks?

1988 924s

Today I fooled around with the car a lot. I completely removed the J Boot this morning and did inspect it. Boot looks good! I also took a look inside the AFM and made sure the "barn" door was not stock and it was not. For ****s and giggles I ordered a fuel pressure reg. That I will get tommrow. Tommrow I plan on going at this car all day from sunrise to sundown. I am going to purge all the fuel lines by jumping the DME relay, change the pressure reg. And study up on how to inspect my belts. I have a daily driver but this car has been my hobby car and dream car for years to fully restore and drive . I am blessed that I was lucky enough to inherit it when my grandfather passed away. He was the original and only of the car and it was always garage kept. Last year I did a lot to the car . water pump, timing belts you name it I probably had changed at my local BMW and Porsche mechanic shop . One day My dream is to buy a 944 turbo , and a Porsche 911 loll big dreams I know but I absolutely love Porsche cars! Sry its late and I am rambling . thanks for the quick reply. Glad to know there is others out there that love these cars like I do and are willing to give helpful advice

1988 924s

Also got to add this... The injectors that I installed were from five 0 motorsports. They are brand new. I read great things about that company . decided to give them a try

Jfrahm

What have you done at the distributor? Check for a loose rotor? It could be a weak spark if the tester does not make the spark jump about 10mm.
Otherwise it's always good to check the cam timing in case it's skipped.

Tom M'Guinn

First, are you sure the new injectors are compatible -- same flow rate, dead time, impedance, etc.? If they are not the same part as the originals, chances are very good that you have introduced an engine management mismatch to some extent. If the factory injectors spray fuel and ohm out ok, I'd revert to those for now. That said, I'd try to diagnose in a logical progression. Start by pulling the No. 1 spark plug wire and seeing it if arcs strongly to ground (i.e., to the intake or nearby grounded metal). If so, then pull a plug and crank the motor to confirm fuel is getting into the cylinders -- you will smell and see it with a flashlight in the spark plug hole. If you're not getting fuel or spark then report back for more on that. Assuming you pass both of those tests (as your previous testing suggests) then the potential problems are in all likelihood quite limited -- either you have a compression or valve timing issue, an ignition timing issue or -- most likely -- your air-fuel ratio is off due to a bad sensor/connector, vacuum leak, or other engine management component. At that point, I'd confirm the cap and rotor are good and tight; confirm the timing belt is aligned; then check the resistance on the DME temp sensor; check the voltage on the AFM (should be near .7v at idle); and check the O2 sensor operation. Clarks-garage has all the test values. If all that checks out, come back for more.

1988 924s

Ok in back with an update . today I worked on the car all day troubleshooting this no start ... I ordered the dme temp sensor that I hear you guys suggesting, a new oxygen sensor, and a new bosh FPR . I pulled up the fuel rail and watched the injectors fire while a friend of mine cranked the car. All injectors fired a nice strong spray pattern. The injectors were purchased from an online vendor of fuel injectors called five 0 motorsports. Great customer service, and shipping was lighting quick! The injectors are the exact resistance and exact spec as the original stock ones. I also have a data flow sheet with the dead times ect. While looking around the idle stabilizer I DID find a vac. Line that was totally disconnected. Cleaned a few grounds that I could find , and made sure the afm barn door was not stuck. My theory is that I am either way to rich or lean to fully fire. .. The car lightly rumbles up like it really wants to start but it will not fully turn over. I am wondering is there a way to simply adjust your mixture on start up? I have good tach bounce, good fuel pressure checked with a gage and proper fitting, spark was confirmed at thecoils using a spark tester light... Hmm maby I have a weak spark? I am fearful that I somehow did some internal mechanical damage to the motor.. Rods valves ect. My compression numbers were solid. 180 180 180 190 . tommeow I plan to check afm voltage, check the starter, check the battery voltage drop.. Could rusty battery terminals cause a no start? Also The ground that attatches to the firewall from the battery is terrible. I plan on changing that tommeow.. Hoping to hear from some of you and will take all your suggestions to heart. Thanks guys!

Tom M'Guinn

I assume you realize you can test all those parts before ordering new ones unnecessarily. Ordering new parts will rules out the part itself, but not the harness connections, etc. so adds little diagnostic info and gets expensive fast. But I get it, been there, done that... You can use the FQS to add/subtract small amounts of fuel. Or, try introducing a vacuum leak to see if the motor needs more air (you can open the ISV port on the side of the intake for example, and perhaps regulate it with a glove-covered thumb). Or add fuel by pulling the vacuum line to the FPR to increase the pressure. Battery terminals shouldn't rust, but as long as you are getting a good solid crank, that's not your issue. Have you confirmed the cam timing marks?

Van

Engine temp sensor for the DME.

jvandyke

We went through similar resurrecting an '87 924s. Coil was bad, severely corroded coil wire. You have spark so probably okay there. Was running, suddenly not, so shouldn't be a timing issue or something. (ours was actually seized when we got it!) We had no baseline at all.
​​​​​​​I'd test all the circuits at the ECU harness that way you test the wiring and the component at the end. Not much help sorry, sure sounds like you're doing your homework though. I'd be leaning toward reference or speed sensor but I wouldn't buy one until I was 90% sure. I HATE buying parts I don't need, especially on a Porsche!

1988 924s

Thanks guys! Glad to see I have help and i am not alone!! Today I had A second to take a quick look at the car. I tried to start her up and on one key turn she fired very strong! Right after it fired it died.. I took yalls advice and decide to take a look at this dme temp sensor. I checked the resistence of the sensor using a multimeter and the resistence was 3.40 ohms. Of course, the motor was cold since I can't start it. The temp. In New Orleans today was around 60 degrees. This resistence seems way off to me. What do u guys think. Tommrow I plan on checking it at the wiring harness. One more thing. . Sometimes when I try to start the car the crank stops and goes flat .. Does that sound like a bad ground?

1988 924s

One more thing. The car for the past few months now would usually be hard to start first start of the day, I would usually have. To keep my foot on the gas to warm it up then it would finally keep an idle. Does this sound like a progressive sensor failure. Also I have noticed at times running prertty rich. Popping out exhaust tail pipe

Tom M'Guinn

You sure it wasn't 3.4K (i.e. 3400) ohms? Some multimeters are hard to read in that regard. 3.4k would be right within spec at 60 degrees. If it was actually 3.4 ohms, then that's way out of spec and would cause the motor to be lean and potentially not start. If the car fires up every time and immediately dies, that does sound like a mixture issue -- big vacuum leak, bad sensor, or guaranteed-to-be-the-same-injectors that aren't. The starter motor stopping when you crank is probably unrelated, and points to either a weak battery or poor connections. Put a trickle charger on it for now to keep it topped off while you sort the no-start issue. Once you have the car running, confirm the battery has 12.6 volts when the motor is not running, and about 13.8 when the car is running. If not, the battery or charging system is probably bad. In the meantime, if you see corrosion on the battery terminals or the main ground cables, by all means clean that up. With the battery topped off, personally I'd eliminate a variable and put stock injectors back in (Five-O is great, but they don't specialize in these cars), then triple check for vacuum leaks, then confirm spark at the plug leads while cranking (and confirm rotor is on tight), then start checking the sensors (at the DME plug to effectively test the harness too) using clarks-garage specs, e.g., temp sensor, AFM, TPS, knock, O2.

Coloradoguy

You might try jumping the DME relays and see if this gives you joy. At least it's inexpensive and easy and eliminates this pesky part of the Porsche non-starting equation.

http://rennbay.com/DME-Relay-Info.html