Hello everyone,
I have a 88 C4 automatic 350 tpi . The guy before me put a bunch of money in it. New plugs,wires, cap,rotor,and new injectors just stock ones from standard ignition products. There is no check engine light on..
I put my scanner on (snap on MT-2500) and the fuel trims are showing it’s running rich .. it was last fall when I last played with it but I believe block learn was around 95 and intergrater was around 75..

Car runs great however after it is hot and I go to start it a hour or so later… it rolls over for maybe 5 to ten seconds before it starts and once it starts I have a rich exhaust smell.
I have been reading up on this issue here on other forums.. a lot of guys mention injectors.. but these are new ones and the guy that changed them said it did this problem before he changed them.
I put a fuel pressure tester on and timed how long it took to drop.. I did it last fall but I think it was about 45 minutes and it dropped 20 psi.. I’ll have to check all this stuff again now that I’m starting to play around with it…
So I changed the heater core this weekend and while I had the computer out I thought I’d check and see if there was a chip in it… and yes there is… the car is stock… manifolds ,exhaust, pollution pump etc… but has a chip in it… I don’t know much at all about high performance chips .. but now I’m wondering if that could be the issue… thanks for reading.

 

Typically , the stock chip is plugged into that aftermarket chip. If that's the case, disconnect the aftermarket chip from the stock chip and plug the stock chip straight into the ECM and see how she runs.

 

Looks like a Jet Chip based on the EO number and circuit board. It most likely adds a little spark advance, reduces the fan on/off temperatures and may raise the tcc lockup speed a bit. ACKY is a 1988 auto trans bin for 2.73 or 3.07 gear.

Suggest you scan it again. The BLM lower limit should be 108, so your numbers don't really jive with what is normal or expected.

 

Thanks guys, I’ll check that out and post the results.. appreciate the info. 93000mi

 

Hi everyone, so I have update,
I managed to get at it today, I scanned with and with out the performance chip installed and there was no difference between the two…
block learn is 108 and intergrater goes as low as 70…so yes tequilaboy is right about that….so is that normal? It runs so rich that it will burn the eyes out… . Other than that it runs great… and it will roll over longer after it sits for a hour…but always starts….I’ll play with it some more like leak down test etc… i did all that last year and ended just driving it… gonna end up doing the same thing this year too lol… however any suggestion is appreciated thanks !!

 

ECM is doing everything in it's power to try to lean things out. But it's still rich. Have you had a fuel pressure gauge on the rail? Does it hold fuel pressure when you shut the key off?

I'm also working on a friend's 88 that's been doing similar things. His car was firing the injectors intermittently with the key in the run position and engine off. I also was not able to connect to the ECM and get a data stream. I determined ECM was bad. It took a few used/rebuilt ECMs to get one in there that seemed to behave and communicate properly. Also, it doesn't appear that anyone makes these ECMs or rebuilds them anymore. I'm referring to the 165 ECMs from 86-89...you have to find something used. It's a crap shoot. I'm not saying that your problem is necessarily a bad ECM. But it might be ...regardless, I would put a fuel gauge on the rail and monitor it for unusual behavior.

Also, if it's pig fat rich when restating with long cranking, try unplugging the 9th injector. Having that injector adding even more fuel while cranking isn't helping.

 

Look at the coolant sensor, MAT sensor, MAP sensor, etc... are they all displaying reasonable values? For a stock 88 Vette, I'd expect the MAP Sensor to be reading about 30-40 kPa at idle in neutral. Key on, engine off... how does the TPS look? Does it increase linearly with application throttle?

What injectors are on the car? Can you see a p/n embossed on the sides? Post a picture of them perhaps? Maybe previous owner put in bigger injectors and didn't update the chip to account for them?

 

Good advice on checking output of all sensors but no MAP sensor until 1990. 88s still running MAF system.

 

Below is a post from a few years ago that I came across while dealing with rich condition on the 88 I'm working on.

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Old Jun 18, 2017 | 06:02 AM
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K87ZZ4
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Default SOLVED! Running rich

A couple of years ago, I posted about a problem I was having with my 87 running rich and occasionally setting a Code 45 (Rich Exhaust), plus the MPG was way off (30-40%) between what the dash showed and what I calculated:

It failed an emissions test, many years ago, so I took it to a shop for diagnosis and they concluded it was the diverter valve in the A.I.R. system (no replacement parts available).

I tried a bunch of things, on my own, to try to figure out what was causing the problem.

• I disconnected (and plugged) the tubes in the A.I.R. system (no difference).
• I replaced the IAC.
• I checked the FPR vacuum hose for fuel (it's dry).
• I put in a new O2 sensor.
• I checked the resistance on the injectors (a pretty consistent 17.6-17.7 ohms each).
• I checked the fuel pressure (42 PSI on prime, running at 40. Holds pressure fine).
• I pulled spark plugs (all pretty fouled with black soot).
• I checked for vacuum leaks (no surges in engine speed).
• I disconnected (and plugged) the lines from the charcoal canister (EECS)(no difference).

I collected data and found the Block Learn (BLM) at 108 nearly all the time, the O2 super high 800+ mv most of the time, and very few cross-counts (Rich ALL the time).

I finally gave up and took it in to a different shop. They ran it through a full battery of tests and decided it must be the ECM because they saw some erratic data and everything else checked out. They replaced the ECM and all is well! It was a case of scrambled brains in the computer! I had wondered if my custom chip could be at fault, but it's running fine with the custom chip now.

Comparing data now, to then, I see the Base Pulse Correction would erratically bounce between 60's to 100's and now it's 120's and 130's most all the time. If I had known more about what I was looking at, and what was 'normal', I *might* have been able to focus on the erratic behavior of the Base Pulse Correction, but I'm not sure I would have concluded that the ECM had lost its mind.

I've read about others with similar symptoms, so I'm posting this just in case my experience helps someone else...

 

Ok so I did pretty well everything that he did in his post last summer. I had checked my fuel pressure with a fuel pressure gauge.. shut it off seen if it held pressure etc… I even eliminated the 9th injector with the delete kit… I will post a pic of the part number of the injector soon when I get back at it… one thing I am gonna do is check the base pulse correction like he mentioned in his post…last year when I was playing around with it I even ran it with the fuel pressure gauge on and opening the relief valve on my pressure gauge while the car was running… letting it shoot gas into a gas can thinking it would start lean it out… but no… lol
I’ll get back at it again and start over and post thanks for reading!!

 

One more thing. Are you getting a Service Engine Soon (SES) light at all? Like when you key on the ignition. Or if you short the A&B pins on the ALDL connector you should get the SES light to at least flash the 1-2 code. Is any of that happening?

Because it isn't happening for me even though I can connect to the data stream. I'm wondering if the SES bulb is out? Anyone know of a good way to test the SES bulb without removing it? I tried by grounding the SES pin on the ECM connector as I believe this is how the ECM illuminates the bulb. It grounds that pin. When I ground it, nothing happens. But I'm also grounding it with the ECM disconnected. Does the ECM supply power AND ground to that bulb? I'd like to test it by forcing it to illuminate through the wiring harness if possible.

 

No service eng soon light on when it’s running, but it does come on with ignition on engine off and that is normal… so if your bulb is good chances could be that your ecm is not getting power…. Wiring diagram would help you a lot… you have one?
There is one thing I should mention I noticed with my car.. I have a snap on MT-2500 scanner.. old school red brick… anyways if I leave it plugged into the diagnostic connector and turn the ignition on with engine off… the check engine light blinks erratically and I hear Solenoids clicking at the same time… only when it’s plugged in.. never seen it happen when it’s not… but will always start regardless.. I have wiring diagrams if you need

 

So I went out to the shop and played with it a bit…took some pics … second pic is the part number on the injector… I remember last year looking that up.. they are apparently just stock injectors from standard …… rest is pics of some readings… it almost feels like the injectors are too big …. But apparently not….

 

Your TPS is a little low at .48V. Should be .54V. I doubt that's your issue, but might a well get it corrected.

Base pulse width is only 1.2ms, so it's not like the ECM is commanding the injectors open an excessively long period of time.

BTW, what is your fuel pressure when the car is running? I didn't see a number in any of the previous posts.

 

I’ll have to check it again, but last summer when I was playing around with it I believe it was 40- 42… I’ll recheck again and post the results.. thanks..

 

The load and mass airflow signals are a bit high for a 625 rpm idle (in park/neutral). I'd say that the MAF calibration is suspect. Delphi sensor?

 

I’m not sure if it is, I’m gonna say no, however it was replaced last year… at that time the check engine light would come on… replaced it with the one that is in it now and the light has not come on since… I might have the box with old one still… I’ll have to look… I know it was 500$ for it new from the local parts store…

 

Something else came to mind… I remember last year there were times I’d go to fill up with gas and when I open the gas cap there was pressure…. But I think I did things like leave the cap open etc and there was no difference…

 

What happens if you create a vacuum leak? Like pull the PVC valve out of the valve cover while it's in closed loop. And/or try removing the PCV valve entirely. Will the O2 voltage drop down and start giving you cross counts?

I ask this because, by doing this, you're bypassing the MAF sensor. So, in theory, I believe... that additional air should enter the engine without commanding additional fuel from the ECM and the mixture should lean out. Currently, your ECM is at its limit of lean correction (108 BLM). If you add additional air through the MAF sensor, that air will command additional fuel from the ECM and you'll be back where you started; which is a rich condition that the ECM cannot mathematically lean out to correct.

 

I'm also noticing your O2 cross counts are zero. Typically the O2 voltage is bouncing around and everytime it crosses 450 mV, ECM registers a cross count.

The only thing is, this could be a symptom of the problem since if you're pegged rich, you might expect the O2 voltage to remain on the rich side of 450mV.