914-SHO Surging RPMs - Issue Solved?

[Flintstone Chaz]

I just looked at the engines in the garage. When I loosen the screws on the TPS it seems like it will rotate just a little. Not much but maybe enough to be a concern in the throttle just off idle case we are talking about.

Gerard, maybe you could put your meter on the TPS and verify a change from closed throttle to your 1800 RPM throttle position.

Just trying to eliminate one more thing.........

Charlie

 

[Shovert]

Since you made the harness, That is reason I would check voltages at backside of connection to computer. That would confirm wiring issue or tps or chasing wrong idea. Maurice

 

[3d914]

My thoughts, Install fuel regulator before the engine since using a differant from Ford. I agree o2 may fouled up. Do you get codes and what? If tps comes up. I would check at computer. I always try and check sensors at the computer especially if I mod the wiring. Easy enough to goof up. If read at computer eliminates wiring problems.

Maurice, Not getting any codes. I did check the TPS -see below.

I assume check for vac leaks. I use a pressurized test to test mine. [learned this doing turbo]. I assume check iac for leaks, also EGR can leak thru. My thoughts, hope that helps. Maurice

Checked all hoses, connections, etc. The EGR port is welded closed on exhaust. I check the vacuum reservoir and the solenoid - both working properly, and secondaries open at startup & close on KO.

I just looked at the engines in the garage. When I loosen the screws on the TPS it seems like it will rotate just a little. Not much but maybe enough to be a concern in the throttle just off idle case we are talking about.

Gerard, maybe you could put your meter on the TPS and verify a change from closed throttle to your 1800 RPM throttle position.

Just trying to eliminate one more thing.........

Charlie

Gotcha, Charlie. Here are my TPS test results:

• Closed throttle should be 0.6v for EEC-IV
  I measured 0.9v
• WOT for EEC-IV is 4.5v
  I measured 4.8v
• I also checked VREF = 5.2v
• I also checked between closed & open throttle and numbers incremented properly with no skips.

Since you made the harness, That is reason I would check voltages at backside of connection to computer. That would confirm wiring issue or tps or chasing wrong idea. Maurice

Good idea. I will add this to the list of checks. Been using back-probe at each component to check.

 

[rubydist]

tweaking the tps that tiny amount won't do anything. here is why:

the pcm looks at the tps voltage at startup and sets that as the value for closed throttle. therefore, if the throttle plate is adjusted open some amount to make the engine run at ~1800 rpm, the pcm will see that tps voltage as "idle" or closed throttle. since 1800 rpm is way to fast for idle, the pcm will then try to get the idle speed to drop down.

the solution for this is to adjust the base idle back to the correct number, and start the engine with the throttle plate closed. after it starts, open the throttle to 1800 rpm and then it should run steady.

 

[Off Road SHO]

I knew a smart guy would chime in on this.

Tom

 

[Flintstone Chaz]

I've got to move out of the carburator era . That makes sense.

Thanks to all. By the time I'm doing the electronics on mine I'll know lots of tricks.

Charlie

 

[hawkeye18]

Vref should be 5.0000 volts. It should not be 5.2v. That may be part of the problem. .9v at idle is not abnormal, though.

 

[Shovert]

Vref I agree. My site says 5.0 +- 0.1 volt.
This is site I use on my 2.3 turbo. Which is eec-iv which is same as SHO. So I assume same as. Page 21 is vref info. Hawkeye18 please confirm I don't want to give bad info. Maurice
http://www.rothfam.com/svo/reference/sensors.pdf

 

[hawkeye18]

Sounds good to me. VREF is supposed to be a conditioned, calibrated voltage output by the EEC to serve as a known reference value from which it derives all of its sensor values. If VREF is too high (or too low), nearly all of your sensors - including your O2 sensors! - will be all out of whack. If VREF is 5.2v, then it will think all of its sensors are reading .2v higher than they really are, and that can cause all sorts of wackiness.

I would read the voltage from the VREF pin (don't know what it is offhand, but others might) on the EEC to the negative terminal of the battery, and see what it is. If it's 5.0V, then there is something adding additional voltage to the line. If it's 5.2V, I would replace the EEC.

 

[rubydist]

I would not worry about 5.2V vs. 5.0V - most of the cheap meters we all have end up having more tolerance than that, unfortunately.

5.2 vs. 5.0 is only 4% variance anyway.

 

[groove83]

Correct me if I'm wrong, but I always thought that fuel pressure went up when the vacuum line was removed from the fpr, not down. I thought it was ~32 Psi at idle with line connected and ~40 Ish psi at WOT and at idle with line removed.

 

[3d914]

Vref I agree. My site says 5.0 +- 0.1 volt.
This is site I use on my 2.3 turbo. Which is eec-iv which is same as SHO. So I assume same as. Page 21 is vref info. Hawkeye18 please confirm I don't want to give bad info. Maurice
http://www.rothfam.com/svo/reference/sensors.pdf

Thanks again Maurice - that's the same one I'm using.

Sounds good to me. VREF is supposed to be a conditioned, calibrated voltage output by the EEC to serve as a known reference value from which it derives all of its sensor values. If VREF is too high (or too low), nearly all of your sensors - including your O2 sensors! - will be all out of whack. If VREF is 5.2v, then it will think all of its sensors are reading .2v higher than they really are, and that can cause all sorts of wackiness.

I would read the voltage from the VREF pin (don't know what it is offhand, but others might) on the EEC to the negative terminal of the battery, and see what it is. If it's 5.0V, then there is something adding additional voltage to the line. If it's 5.2V, I would replace the EEC.

hawkeye, I suspect - as ruby suggests - that my DVM is easily off by .2v, but I like your idea of rechecking them at the PCM connector. Maurice suggested the same. I'll go ahead do that and compare those results with the others I've noted. If they are different at least it will suggest that I've got something crossed.

I know how to look for a voltage drop, but not sure how to look for a voltage increase - especially that small.

 

[3d914]

Correct me if I'm wrong, but I always thought that fuel pressure went up when the vacuum line was removed from the fpr, not down. I thought it was ~32 Psi at idle with line connected and ~40 Ish psi at WOT and at idle with line removed.

groove, on my second test it does go up with the vacuum line removed. I have them listed backwards - so maybe that threw ya.

Second test - hour later.

1. KOEO, Check fuel pressure - should be 31-41 psi.
   Mine jumps to just over 40psi then settles to 38psi. This is with the return fuel line crimped to maintain some back-pressure. If I KOEO again, it jumps to 40psi again.
2. With engine running, check fuel pressure at idle with vacuum line at regulator removed - should be 22-32 psi.
   Measures 42psi with vacuum line removed.
3. With engine running, check fuel pressure at idle with vacuum line at regulator connected - should be 28-34 psi.
   Measures 32psi with vacuum line connected.

 

[3d914]

After long last - Yee Ha - I've got a good running SHO! :woo-hoo:

Spent the weekend working out the final bugs, here's what it took:

• Added shielding for DIS cable extensions
• Fixed cracked and separated shielding in stock engine harness
• Fixed an intermittent main ground. Pin in plug was not seating completely. Sometimes had continuity, sometimes not.
• Similar pin problem with Coolant temp sensor. Replaced it with a spare I had.

Rechecked O2 output and its now steady and w/in spec. Fuel pressure is holding properly. I need to recheck the IAC valve on a cold-start because the last values I got over the weekend didn't look good.

But it's sounding really good. The little bit of hunting at idle I think has to do with run time. I just need to get more time for the PCM to register settings.

Here's an updated video.

:woo-hoo:

 

[intimdatr]

Whoo oohh!! About time!!

 

[Shovert]

Awesome. Great to hear. Wiring can be a pain. Especially a bad connection. We all got to remember these cars and parts are pushing almost 20 years, Even wires in bundle can go bad. Maurice