Persistent no start--at the end of my rope!

[danny boy]

Hey all,

This comanche is driving me insane. First off, 1989 4.0 manual.

This began when it drove to work fine (3 months ago!) and then about 100 yards after leaving on the way home it starts to sputter and die. It would start but as soon as you tried to move it would die. I pushed it back to work lot and it sat.

I recently tried a temporary hard wire of fuel pump in order to test. I jumped it and it started but wouldn't idle or accept more throttle. Then swapped out CPS.

Yesterday I checked and found the center contact in the dist. cap was missing. Replaced cap and rotor so I got spark against the block. Plugs very sooty black. Used a jumper wire to bypass fuel relay and got fuel at the schraeder valve. SO.... I've go spark and fuel, but no fire. What the heck? I'm now wondering if whatever tells the injectors to squirt isn't doing so.

What is going on with this thing?

p.s. it has orange ford injectors and a tps from an automatic. I tested MAP sensor and it is good.

HELP!

Dan

 

[87manche]

if you've got spark then it's got the proper signals to trigger injector pulses.

Did you replace the black and sooty plugs?

obviously it's runnig very rich or has a very weak spark. What did the spark look like when you tested? SNappy and blue? If it was weak and yellow replace the coil.

Have you adjusted the TPS for the reference voltage?
Have you tested the fuel pressure?

 

[90xj06]

i don't know how or where you jumped your fuel pump. but you have a ballast resistor. if it starts fine and let go of the key sputters a minute and dies its either bad or has become disconnected.

it should be on the left side of the engine compartment. its a white rectangle with 2 (orange) wires coming off of it.

if its connected you can temperately jump the 2 wires together to see if it will run.

 

[joe_peters]

Ok.

First, pull the battery and have it fully charged--its been sitting and we don't know the state of charge.

The Renix has to "spin up" to 300+ RPMs before the crank sensor will generate a strong enough signal for the ECU to fire the spark. You need a strong cranking engine.

Second, put some new clean plugs in there.

Third, use a plug grounded to the engine and check the condition of the spark--HOT, BLUE, and SNAPPY is good.

Fourth, why do you have black sooty plugs? Check the vacuum line from the throttle body to the MAP sensor on the firewall.

Post up the results.

 

[lawsoncl]

Being a Renix, I'd say check the grounds, especially the block-firewall strap as it rots out and causes strange problems like this. If you think it's intermittent spark, maybe pull the coil off the ignition module and cleanup those contacts as well.

 

[cruiser54]

Great advice from Joe and lawsoncl. Do what they suggest first.

If the distributor cap was that bad, I can only imagine the condition of the plug wires.

 

[Molten Metal]

I've had one do that before. And I let it sit, but I left the battery disconnected. A week later I thought I'd try it and never had another problem. Did you disconnect your battery when it was parked?

 

[Molten Metal]

Its my understanding that the ecm returns to a Limp mode until it gathers all the info it requires to run efficiently, basically just starts over. It may help.

 

[cruiser54]

Renix ECU is not adaptive. Battery disconnects have no effect at all.

 

[Ecomike]

I am curious about the old damaged cap? Was there any other sign of a wobbling distributor shaft?

I have seen empirical evidence that disconnecting the battery clears up some Renix problems, that leads me to believe that it has some sort of volatile sensor data memory that it stores beyond just the KAM memory. The Renix ECU and TCU both have a direct connection to the battery positive (through a fuse link) that is independent of (bypasses) the ignition switch, which I believe is involved in helping the ECU and TCU to store volatile memory. I have also noticed that just cycling the ignition switch on/off (starting or not starting) seems to clear the memory of prior funky data (especially after replacing or re-calibrating a TPS) as well, if done exactly 3 times.

MM, the Renix always starts in a sort of limp mode (ignores the O2 sensor), and then once the O2 sensor is hot enough, the ECU tries to enter closed loop mode. That so called limp mode is most often called open loop (it ignores the O2 sensor).

 

[lawsoncl]

MM, the Renix always starts in a sort of limp mode (ignores the O2 sensor), and then once the O2 sensor is hot enough, the ECU tries to enter closed loop mode. That so called limp mode is most often called open loop (it ignores the O2 sensor).

Also if the engine computer tries to adjust to the engine of its range of lean or mix based on the O2 sensor, it will fault and go back into open loop mode.

Another bit of mis-information floating around. The Renix ECU does actually store fault codes, but you need a DRB-II to read the codes and they go away after 15 key-off/on cycles. So they are there but nearly impossible to get to.

Your sooty plugs may indicate you're running excessively rich in open loop. Do those orange tips flow more than stock at the same pressure? Fuel pressure regulator working? Tested fuel pressure with a gauge? You might also check that the EGR value is working as that can cause crappy idle and running.

 

[old_man]

Another bit of mis-information floating around. The Renix ECU does actually store fault codes, but you need a DRB-II to read the codes and they go away after 15 key-off/on cycles. So they are there but nearly impossible to get to.

I think you are the one with the misinformation. I have been working on Renix vehicles for over 12 years and have the SnapOn Scanner. The Renix units are not DRB-II. That started in 91 and ran to 96 IIRC.

 

[lawsoncl]

Then it's the Renix Fuel Injection manual that's wrong. I'm looking at pages 84 thru 86 and 88 of "4.0 Liter Multi-Point Fuel Injection (1987-1990 RENIX System)" in case you have a copy. It states that faults are stored in the Keep Alive Memory for 15 key-on/off cycles.

The bottom of page 88 makes it pretty clear that DRB II can be used on Renix.

"Use the DRB II diagnostic tester along with Jeep/Eagle adapter #0T53129 on all 1987 - 1990 fuel injected models. Refer to the Powertrain Diagnostic Procedure manuals for fault codes and test procedures. The DRB II diagnostic tester and adapter will be able to perform System Tests, State Display, and Throttle Position Sensor (TPS) adjustments on the fuel system. The DRB II will also be able to display faults that can be stored in the ECU'S "ON BOARD" diagnostics."

 

[lawsoncl]

The Renix units are not DRB-II. That started in 91 and ran to 96 IIRC.

I bet you're thinking OBD-II?

 

[Ecomike]

I bet you're thinking OBD-II?

X2 on that.

 

[joe_peters]

Yes, the DRB, DRB II, and I THINK the DRB III can all be used on the Renix.

The fault codes that are "stored" in the KAM--Keep Alive Memory are extremely limited in number, and they aren't exactly "stored"--they are counted, and the count for any "stored" code changes up or down (added and subtracted) up to a maximum of 15 total "counts".

Now, if you are lucky(?) enough to have spent $600+ on a used DRB scanner you can read the "count" of those fault codes. I haven't seen a used DRB II on the market so no idea what those are going for. A new DRB III runs over $5000.

Not sure if the MT2500 "brick" allows you to access the "counts"--maybe someone with a brick will post up and let us know.


What the ECU checks and will "count":

MAT--checks that the sensor voltage is within limits (checks for open/short condition).

CTS--same as MAT.

TPS--same as MAT/CTS.

MAP--same as MAT/CTS/TPS.

Now, I can tell if a sensor is shorted or open with a multimeter that costs $1.99 at Harbor Freight.

But yes, Virginia, there really IS a Santa Claus, and yes, the Renix ECU "stores" a count of the open/short condition of four sensors--MAP/CTS/TPS/MAT up to a maximum fault count of 15, adding and subtracting each time the fault exists (adds) or doesn't exist (subtracts).

Not a very useful function, and worthless without a DRB tool--which only a very, very, very, very few have access to outside of a dealership.

EMERGENCY UPDATE: there is a "buy it now" of $2495.00 for a DRB III scanner on eBay!! Be the first to own one! Amaze your friends!

 

[Ecomike]

Yes, the DRB, DRB II, and I THINK the DRB III can all be used on the Renix.

The fault codes that are "stored" in the KAM--Keep Alive Memory are extremely limited in number, and they aren't exactly "stored"--they are counted, and the count for any "stored" code changes up or down (added and subtracted) up to a maximum of 15 total "counts".

Now, if you are lucky(?) enough to have spent $600+ on a used DRB scanner you can read the "count" of those fault codes. I haven't seen a used DRB II on the market so no idea what those are going for. A new DRB III runs over $5000.

Not sure if the MT2500 "brick" allows you to access the "counts"--maybe someone with a brick will post up and let us know.


What the ECU checks and will "count":

MAT--checks that the sensor voltage is within limits (checks for open/short condition).

CTS--same as MAT.

TPS--same as MAT/CTS.

MAP--same as MAT/CTS/TPS.

Now, I can tell if a sensor is shorted or open with a multimeter that costs $1.99 at Harbor Freight.

But yes, Virginia, there really IS a Santa Claus, and yes, the Renix ECU "stores" a count of the open/short condition of four sensors--MAP/CTS/TPS/MAT up to a maximum fault count of 15, adding and subtracting each time the fault exists (adds) or doesn't exist (subtracts).

Not a very useful function, and worthless without a DRB tool--which only a very, very, very, very few have access to outside of a dealership.

From what I know of computer process control algorithms, I suspect the the Renix ECU defaults to a fixed table value and ignores a sensor with a 15 count, or one that is supplying bad data that is beyond values assigned in another list as upper and lower reality check limits. Just because Renix and DRBs were not set up to show us stored memory data of current or prior operation sensor reading limits, does not prove that Renix is not storing and using that data.

My daughter made the mistake of running the radio in the 89 one day in the run position on the ignition switch. When I got back, I turned it off, waited 15 seconds, turned it on, waited 5 seconds than cranked it. The idle ran up to 4000 rpm and held! The idle had been working perfectly before that. I turned it off, then cycled the ignition switch to on/off, 3 times in a row, for 15 seconds at each point. I restarted the jeep, and the idle was perfect, and gave me no more trouble for 6-12 months.

Just disconnecting, and reconnecting a TPS on a running renix seems to reset something in the ECU memory. Of course that is live operation, and another story, but why would they supply 12 volts to the ECU 24/7/365 if it was not for storing memory. I wonder how the algorithm uses the 0 to 15 count? Perhaps it uses it to discount that sensors data in number crunching for timing and fuel rates, in favor of a default table value.

Re-reading page 85 and 86, the manual clearly says that ignition on, engine off, it is possible to read the Engine State Display Function (with the DRB-**), and read the min/cur/max readings of all the engine sensors. That can only happen if renix is storing on going min and max sensor values from prior engine running states. I know that disconnecting and reconnecting the TPS on a high idle renix, can have a huge effect on the idle before versus after reconnecting the same TPS at idle.

What I have not figured out, is why my 87 and 89 renix act differently when I disconnect the TPS, and then try to gas the engine throttle. My 89 does not seem to care, unless I really gas it fast. The 87 pukes and chokes and shakes with just a little slow movement of the throttle.

Anyway, we did ever get OPs renix started?

 

[cruiser54]

I'll have to try the ignition on, engine off with my DRB hooked up. I've only ever read the state display with the engine running.

 

[Ecomike]

I'll have to try the ignition on, engine off with my DRB hooked up. I've only ever read the state display with the engine running.

COOL! Be looking forward to hearing what you find. Be sure to disconnect a sensor or two and see how it reacts, and the data it stores and shows between cycles!

 

[cruiser54]

Sorry. Just reads the sensor in real time. No min/max in the display. I can tell you that the air temp in my manifold is 65* and my coolant is at 55*, while my TPS is at 13%.

Start it and the "state display" still shows real time with no min/max also.