depami

I also bought Bosch injectors from Five O Motorsports. Turns out I didn't use them. They are the top row of the first image in >>> this post <<< and flow data in third image. If anyone is interested in them, send me a message.

ianbsears

Don't know if you have checked or replaced the timing belt or not. If it skipped any teeth it could be causing this. A compression test would be the tell as one bank would be significantly off spec versus the other bank.

I'm new to the 8 cylinder P Car world but this is what happened with my 928 as it came back to life from a 40 year slumber.

Cheers

Mrmerlin

with the engine running use a long screwdriver and place it on each injector,
listen for it clicking,
if its not clicking then its not putting out any fuel .

What lower O rings did you use?
NOTE the stock tan O rings are a certain size,
and I do not believe that they have been exactly duplicated.

There are some O rings that are close to the correct size .

That said using the non stock O rings will increase the possibility of intake leaks at the injectors

When you removed the old injectors did any powder coating come out with the injectors?

jcorenman

This is a really good thought. Adam (the OP) previously posted that the car had sat for 20 years, and he changed the timing belt after acquiring it. It's pretty easy to be off a tooth or two on one or both sides, especially for a first-timer. A compression test would answer that quickly, an early '87 should be ballpark 140 all around and left-to-right.

Another quick check is to rotate the engine (manually, clockwise facing the motor) to 0-deg TDC on the balancer, then pull the intake tubes off both belt-covers and check that the notches line up.
This is from pg. 15-31 of the Workshop Service Manual (WSM):

As for injectors: Stick with stock, get them cleaned and flow-tested, install them without delay (the cleaning solution can cause corrosion over time), drive the car regularly and use top-tier fuel, not the cheap stuff that you might put in the daily-driver. There are other 19# injectors available, but flow-rate is only half the picture. Latency (opening time, dead time) is the other factor and varies between designs. This changes the amount of fuel injected per pulse, yet is never included in the specs.

Cheers,

heyadamhey

Hi all, I've pasted a few photos of the engine bay below as per @Mrmerlin 's request. You'll likely notice the broken knock sensor plug. I do intend on replacing both knock sensors primarily for the plugs, but the wires are connected in the correct order, so I didn't *think* this would cause the idling/revving issue. Maybe it would throw out the timing?

I fired it up again yesterday and got it up to temperature and it idled a lot smoother. Still bogs down with a jab of throttle though. The fact that it will idle smoothly when warm suggests to me that the injectors are working as they should. So could this be because of that temp sensor causing the fuel mix to be wrong when cold?
I did link to the o-rings I used in the opening post. They're as close to the stock size as I could find and they fit really snugly into the manifold. Top orings are the ones that came on the injectors which also fit snugly in the fuel rail
I did do the TB/WP job when I got the car in October last year. I drove it around the block and the engine ran smoothly, but was down on power. I don't think I got the TB a tooth out, but a compression test is a good idea and it would be great to confirm whether I got the TB back on correctly. I was very careful to follow the how-to guide (on Rennlist) to the letter. I can't remember the name of the author, but it's a brilliant resource.
I have not done the O2 sensor, but I'll put that on the list.
Sounds like the LH computer needs to be on the list too

jcorenman

Thanks for the pics, very helpful.
Non-functional knock sensors will retard timing up to 6 deg, less at idle. This would not cause the idle/revving issue but will be "down on power".

But what I am seriously not liking is the damaged cable at the MAF connector, I would move that to #1 on the suspect list:



If the MAF wires are broken or shorted then the LH will go into a "limp" mode, a fixed injector pulse-width with enough fuel to let the engine run, barely. That may be what is happening. Take a careful look, if there are exposed or broken wires then that needs to be addressed before anything else. The MAF is critical.
Yes on the injectors being functional, but tells you nothing on whether they are appropriate for the engine. If the temp-II sensor was defective/miswired then that will cause fueling problems. You can check this from the LH connector, see pg. D24-14 of the WSM (pg. 619 of the PDF).
The lower o-ring will cause an air leak and lean mixture, if they fit snugly then they are likely good. Problems occur with incorrect o-rings, or a refinished manifold where paint or powder-coat has reduced the hole diameter. (Not an issue here). An upper o-ring issue will leak fuel and start a fire, snug is good and be sure the clips are fitted properly.
Easy to check...
If it has never been rebuilt then yes, but lower priority I think.

Michael Benno

You have put a lot of effort into the car so far, and you will definitely be able to figure this out. Because there are so many things that could lead to your rough running and bogging down issues, I would recommend a systematic approach to testing and troubleshooting. The WSM provides a sequence of tests that need to be performed in order to help rule out contributing factors. You can find these guides here: WSM Manuals 1 through 7 Consolidated (See manual 1A) and available as a separate guide: Test Plan EZK and LH '87. They use a diagnostic grid that has the symptoms you have and the respective tests to be performed in the respective order.


Based on your description, you have up to three symptoms, which, unfortunately, hit all the test points. I created a spreadsheet version of the above grid to help filter the rows to only the items I need. You can save a copy for yourself if you like (get if here) I'd recommend going through each of the tests so you can verify which items are working and which may be problematic. The tests are thorough, and these are the components and the connectivity.

heyadamhey

Thanks for all the feedback! Much appreciated.
Yeah, I didn't like the appearance of that MAF connector either, but the wires are intact from what I recall It makes total sense that it could cause major issues. I have no idea how to repair/refurbish the connector though. I'll have a close look today and take some photos.
My buddy has a compression tester, so I'm going to do that too

heyadamhey

Thanks so much!

I really appreciate all of you taking the time to look and make suggestions. I'm a total noob with 928s, but pretty hand with a wrench. I've owned four classic Minis in my time, so I had to learn Obviously the 928 is a different beast entirely. I can't wait to experience it properly...

Michael Benno

Adding to the helpful comments that @jcorenman added, the test sequence I provided above will help address all of these issues, There is a connectivity test for the MAF harness. Temp sensor tests for performance and connectivity.

Here is a tip on vacuum leaks, since they keep coming up and they can cause so many issues. A healthy intake manifold will NOT LEAK when doing the WSP pressure test. Another simple test is to measure manifold vacuum at wam idle you should see 17-20InHg at least. Also, in your troubleshooting, you may want to isolate/cap the vacuum feed to the brake booster and HVAC because those systems can bleed off the manifold vacuum if they leak. Given the adge of your intake, I would expect you to have small leaks from the bearings used on the throttle plate and flappy because the rubber O rings have degraded.

Michael Benno

DYI manifold pressure tester
https://rennlist.com/forums/diy-928/...ml#post6285151
Or buy one: https://rennlist.com/forums/928-foru...-for-sale.html

hacker-pschorr

https://928srus.com/products/6-way-m...f8a9237c&_ss=r

heyadamhey

hahah I just found that a couple of minutes ago while looking for a temp II sensor. I think I'm gonna get both regardless of whether the current Temp II sensor is ok. At $20ish, it's not going to break the bank

hacker-pschorr

As mentioned already, it would be a very good idea to get the LH rebuilt before you need it done.

Michael Benno

Regarding the MAF connector. Hold off on replacing it until you have had a chance to inspect it. The boot usually fails but the wires usually remain intact. It is far better to "repair the boot" than to cut and reconnect a new connection.

Strip off the boot and unnecessary crunchy glue and inspect the connector, If should look like this. If your wires look good, get some vulcanizing electrical tape/silicon self fusing tape (available at auto parts stores) and wrap it tight. You will find this offers a more compact and flexible boot.

Start the wrap on the wire harness housing about 1.5" from the end of the sheeting. Wrap spirally, working towards the connector using 50% overlap, and finish on the connector using extra tension to ensure strong adhesion and seal.


Also, a protip from @PorKen, remove the metal retaining clip on the connector while doing your troubleshooting to allow for more convenient removal of the MAF. Actually both Ken and I have left that clip off because the connector is plenty tight.

Temp II Sensor Tests
Also, it's super easy to test the Temp II sensor. Also important is that the harness is a common failure point, as is ground connectivity. Remove the sensor, clean it thoroughly, and bench test it. Clean the mounting point to the water bridge, and don't use sealant; only use a conductive crush ring. Do a conductivity test of both wires to the LH and EZK.

Temp sensor (Bosch 0 280 130 032)
25*C = 2135 ohms
30*C = 1735 ohms
40*C = 1225 ohms
50*C = 829 ohms
60*C = 649 ohms
70*C = 477 ohms
80*C = 394 ohms
90*C = 298 ohms
100*C = 219 ohms